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#REDIRECT [[Forest fire]]
{{Short description|Uncontrolled fires in rural countryside or wilderness areas}}
{{Other uses}}
{{redirect2|Brushfire|Forest fire|other uses|Brushfire (disambiguation)|and|Forest fire (disambiguation)}}
{{Use dmy dates|date=August 2019}}
[[File:Burnout ops on Mangum Fire McCall Smokejumpers.jpg|thumb|upright=1.5|Wildfire burning in the [[Kaibab National Forest]], [[Arizona]], United States, in 2020. The [[Mangum Fire]] burned more than {{convert|70,000|acres|km2}} of [[forest]].]]
{{Pollution sidebar|Natural}}

A '''wildfire''', '''forest fire''', '''bushfire''', '''wildland fire''' or '''rural fire''' is an unplanned, uncontrolled and unpredictable [[fire]] in an area of [[Combustibility and flammability|combustible]] [[vegetation]].<ref name="Cambridge">{{cite book | title = Cambridge Advanced Learner's Dictionary | edition = Third | publisher = Cambridge University Press <!-- see http://assets.cambridge.org/97805218/58045/frontmatter/978052roni alonti
f page 5 --> | date = 2008 | url = http://dictionary.cambridge.org/define.asp?key=90587&dict=CALD | isbn = 978-0-521-85804-5 | url-status = live | archive-url = https://web.archive.org/web/20090813154617/http://dictionary.cambridge.org/define.asp?key=90587&dict=CALD | archive-date = 13 August 2009 | df = dmy-all }}</ref><ref name="CIFFC Glossary">{{cite web |title=CIFFC Canadian Wildland Fire Management Glossary |url=https://www.ciffc.ca/sites/default/files/2019-03/CIFFC_Canadian_Wildland_Fire_Mgmt_Glossary_2017_10_24.pdf |website=Canadian Interagency Forest Fire Centre |access-date=16 August 2019}}</ref> Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire ([[bushfires in Australia|in Australia]]), desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire.<ref name="Cbbcco.uk">{{Cite web|url=https://www.bbc.co.uk/fire/earth/natural_disasters/forest_fire|work=BBC Earth |title=Forest fire videos – See how fire started on Earth|archive-url=https://web.archive.org/web/20151016185535/http://www.bbc.co.uk/science/earth/natural_disasters/forest_fire|archive-date=16 October 2015|url-status=dead|access-date=2016-02-13}}</ref> Some natural forest ecosystems [[Fire ecology|depend on wildfire.]]<ref name="Fire Tree Mortality222">{{cite web |title=Drought, Tree Mortality, and Wildfire in Forests Adapted to Frequent Fire |url=https://nature.berkeley.edu/stephenslab/wp-content/uploads/2018/01/Stephens-et-al.-Fire-Tree-Mortality-BioSci-2018.pdf |access-date=15 March 2022 |website=UC Berkeley College of Natural Resources}}</ref>

Wildfires are distinct from beneficial human usage of wildland fire, called [[controlled burn|controlled or prescribed burning]], although controlled burns can turn into wildfires.

[[Fossil]] [[charcoal]] indicates that wildfires began soon after the appearance of terrestrial plants approximately 419 million years ago during the [[Silurian]] period.<ref>{{Cite journal|last1=Scott|first1=Andrew C.|last2=Glasspool|first2=Ian J.|date=2006-07-18|title=The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration|journal=Proceedings of the National Academy of Sciences|language=en|volume=103|issue=29|pages=10861–10865|doi=10.1073/pnas.0604090103|issn=0027-8424|pmc=1544139|pmid=16832054|bibcode=2006PNAS..10310861S|doi-access=free}}</ref> Earth's carbon-rich vegetation, seasonally dry climates, atmospheric [[oxygen]], and widespread lightning and volcanic ignitions create favorable conditions for fires.<ref name=":0">{{Cite journal |last1=Bowman |first1=David M. J. S. |last2=Balch |first2=Jennifer K. |author-link2=Jennifer Balch |last3=Artaxo |first3=Paulo |last4=Bond |first4=William J. |last5=Carlson |first5=Jean M. |last6=Cochrane |first6=Mark A. |last7=D’Antonio |first7=Carla M. |last8=DeFries |first8=Ruth S. |last9=Doyle |first9=John C. |date=2009-04-24 |title=Fire in the Earth System |journal=Science |language=en |volume=324 |issue=5926 |pages=481–484 |bibcode=2009Sci...324..481B |doi=10.1126/science.1163886 |issn=0036-8075 |pmid=19390038 |s2cid=22389421}}</ref> The occurrence of wildfires throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna.<ref name=":02">{{Cite journal |last1=Bowman |first1=David M. J. S. |last2=Balch |first2=Jennifer K. |author-link2=Jennifer Balch |last3=Artaxo |first3=Paulo |last4=Bond |first4=William J. |last5=Carlson |first5=Jean M. |last6=Cochrane |first6=Mark A. |last7=D’Antonio |first7=Carla M. |last8=DeFries |first8=Ruth S. |last9=Doyle |first9=John C. |date=2009-04-24 |title=Fire in the Earth System |journal=Science |language=en |volume=324 |issue=5926 |pages=481–484 |bibcode=2009Sci...324..481B |doi=10.1126/science.1163886 |issn=0036-8075 |pmid=19390038 |s2cid=22389421}}</ref>

Wildfires are often classified by characteristics like cause of ignition, physical properties, combustible material present, and the effect of weather on the fire.<ref name="UToronto">{{cite journal|last=Flannigan|first=M.D.|author2=B.D. Amiro|author3=K.A. Logan|author4=B.J. Stocks|author5=B.M. Wotton|name-list-style=amp|date=2005|title=Forest Fires and Climate Change in the 21st century|url=https://www.firelab.utoronto.ca/pubs/2005_flannigan_wotton_etal.pdf|url-status=dead|journal=Mitigation and Adaptation Strategies for Global Change|volume=11|issue=4|pages=847–859|doi=10.1007/s11027-005-9020-7|s2cid=2757472|archive-url=https://web.archive.org/web/20090325095123/https://www.firelab.utoronto.ca/pubs/2005_flannigan_wotton_etal.pdf|archive-date=25 March 2009|access-date=26 June 2009}}</ref> Wildfire behavior and severity result from a combination of factors such as available fuels, physical setting, and weather.<ref>Graham, ''et al.'', 12, 36</ref><ref>''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', 4–6.</ref><ref name="FireBehavior">{{cite web|url=http://www.nwcg.gov/pms/pubs/410-2/appendixB.pdf|title=National Wildfire Coordinating Group Fireline Handbook, Appendix B: Fire Behavior|date=April 2006|publisher=National Wildfire Coordinating Group|access-date=11 December 2008|url-status=live|archive-url=https://web.archive.org/web/20081217125737/http://www.nwcg.gov/pms/pubs/410-2/appendixB.pdf|archive-date=17 December 2008}}</ref><ref>{{Cite journal|last1=Trigo|first1=Ricardo M.|last2=Provenzale|first2=Antonello|last3=Llasat|first3=Maria Carmen|last4=AghaKouchak|first4=Amir|last5=Hardenberg|first5=Jost von|last6=Turco|first6=Marco|date=2017-03-06|title=On the key role of droughts in the dynamics of summer fires in Mediterranean Europe|journal=Scientific Reports|language=en|volume=7|issue=1|pages=81|doi=10.1038/s41598-017-00116-9|issn=2045-2322|pmc=5427854|pmid=28250442|bibcode=2017NatSR...7...81T}}</ref> Climatic cycles that include wet periods that create substantial fuels and then are followed by [[drought]] and heat often proceed severe wildfires.<ref>{{Cite journal|last1=Westerling|first1=A. L.|last2=Hidalgo|first2=H. G.|last3=Cayan|first3=D. R.|last4=Swetnam|first4=T. W.|date=2006-08-18|title=Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity|journal=Science|language=en|volume=313|issue=5789|pages=940–943|doi=10.1126/science.1128834|issn=0036-8075|pmid=16825536|bibcode=2006Sci...313..940W|doi-access=free}}</ref> These cycles have intensified by [[climate change]].<ref name=":16">{{cite book |last1=Parmesan |first1=Camille |title=Climate Change 2022: Impacts, Adaptation and Vulnerability |last2=Morecroft |first2=Mike |last3=Trisurat |first3=Yongyut |publisher=[[Intergovernmental Panel on Climate Change]] |series=Contribution of Working Group II to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |location= |chapter=Chapter 2: Terrestrial and Freshwater Ecosystems and their Services |display-authors=etal |chapter-url=https://report.ipcc.ch/ar6wg2/pdf/IPCC_AR6_WGII_FinalDraft_Chapter02.pdf}}</ref>

Naturally occurring wildfires<ref>{{Cite journal |last1=Heidari |first1=Hadi |last2=Arabi |first2=Mazdak |last3=Warziniack |first3=Travis |date=August 2021 |title=Effects of Climate Change on Natural-Caused Fire Activity in Western U.S. National Forests |journal=Atmosphere |language=en |volume=12 |issue=8 |pages=981 |bibcode=2021Atmos..12..981H |doi=10.3390/atmos12080981 |doi-access=free}}</ref> may have beneficial effects on native vegetation, animals, and ecosystems that have evolved with fire.<ref name=":1">{{Cite web |title=The Ecological Importance of Mixed-Severity Fires – ScienceDirect |url=http://www.sciencedirect.com/science/book/9780128027493 |url-status=live |archive-url=https://web.archive.org/web/20170101205343/http://www.sciencedirect.com/science/book/9780128027493 |archive-date=1 January 2017 |access-date=2016-08-22 |website=www.sciencedirect.com}}</ref><ref name=":2">{{Cite journal |last=Hutto |first=Richard L. |date=2008-12-01 |title=The Ecological Importance of Severe Wildfires: Some Like It Hot |url=https://scholarworks.umt.edu/biosci_pubs/279 |journal=Ecological Applications |language=en |volume=18 |issue=8 |pages=1827–1834 |doi=10.1890/08-0895.1 |issn=1939-5582 |pmid=19263880}}<!--https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=1280&context=biosci_pubs--></ref> Many plant species depend on the effects of fire for growth and reproduction. <ref name="NOVA222">{{cite web |author=Stephen J. Pyne |title=How Plants Use Fire (And Are Used By It) |url=https://www.pbs.org/wgbh/nova/fire/plants.html |url-status=live |archive-url=https://web.archive.org/web/20090808123751/http://www.pbs.org/wgbh/nova/fire/plants.html |archive-date=8 August 2009 |access-date=30 June 2009 |publisher=NOVA online}}</ref> Some natural forest are dependent on wildfire.<ref name="Fire Tree Mortality22222">{{cite web |title=Drought, Tree Mortality, and Wildfire in Forests Adapted to Frequent Fire |url=https://nature.berkeley.edu/stephenslab/wp-content/uploads/2018/01/Stephens-et-al.-Fire-Tree-Mortality-BioSci-2018.pdf |access-date=15 March 2022 |website=UC Berkeley College of Natural Resources}}</ref> High-severity wildfire may create [[complex early seral forest]] habitat (also called "snag forest habitat"), which may have higher species richness and diversity than an unburned old forest.

Alternatively, wildfires in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have strongly negative [[ecology|ecological]] effects.<ref name="UToronto" /><sup>[Source does not support]</sup>

Human societies can be severely impacted by fires. Effects include the direct health impacts of smoke and fire, destruction of property(especially in [[wildland–urban interface]]s) economic and [[ecosystem service]]s losses, and contamination of water and soil.<ref name=":16" /> There are also significant indirect or second-order societal impacts from wildfire, such as demands on utilities to prevent power transmission equipment from becoming ignition sources, and the cancelation or nonrenewal of homeowners insurance for residents living in wildfire-prone areas.<ref>{{Cite journal|last1=Auer|first1=Matthew R. |last2=Hexamer|first2=Benjamin E. |date=18 July 2022 |title=Income and Insurability as Factors in Wildfire Risk |journal=Forests |language=en |volume=13 |issue=7 |pages=1130 |doi=10.3390/f13071130 |issn=1999-4907 |doi-access=free }}</ref>

Wildfires are among the most common forms of [[natural disaster]] in some regions, including [[Siberia]], [[California]], and [[Australia]].<ref>{{Cite web|url=https://lao.ca.gov/Publications/Report/3918|title=Main Types of Disasters and Associated Trends|website=lao.ca.gov|date=January 10, 2019|publisher=[[Legislative Analyst's Office]]}}</ref><ref>{{Cite web|url=https://www.smithsonianmag.com/smart-news/siberian-wildfires-cause-record-pollution-send-smoke-us-180975275/|title=The Far-Reaching Consequences of Siberia's Climate-Change-Driven Wildfires|first=Theresa|last=Machemer|date=July 9, 2020|website=Smithsonian Magazine}}</ref><ref>{{Cite web|url=https://www.ga.gov.au/scientific-topics/community-safety/bushfire|title=Bushfire|first= Government Geoscience|last=Australia|date=25 July 2017|website=www.ga.gov.au}}</ref> Areas with [[Mediterranean climate]]s or in the [[taiga]] biome are particularly susceptible. At a global level, human practices have made the impacts of wildfire worse, with a doubling in land area burned by wildfires compared to natural levels.<ref name=":16" /> Since records started at the beginning of the 20th century, wildfires have steadily declined.<ref>{{cite web |date=2020 |title=Fires, Forests and the Future |url=https://wwfeu.awsassets.panda.org/downloads/wwf_fires_forests_and_the_future_report.pdf |access-date=31 October 2022 |publisher=[[World Wide Fund for Nature]] |language=en |quote=The area of land burned globally has actually been steadily declining since it started to be recorded in 1900}}</ref>

Humans have impacted wildfire through [[climate change]], [[land-use change]], and [[wildfire suppression]].<ref name=":16" />

The increase in severity of fires<ref>{{cite web | url=https://crsreports.congress.gov/product/pdf/IF/IF10244 |title=Wildfire Statistics |publisher=Congressional Research Service| year=2022|access-date=19 October 2022
}}</ref> creates a [[Positive feedback|positive feedback loop]] by releasing [[Carbon sequestration|naturally sequestered carbon]] back into the atmosphere, increasing the atmosphere's [[greenhouse effect]] thereby contributing to climate change.<ref name=":16" />

Modern [[forest management]] often engages in [[controlled burn|prescribed burn]]s to mitigate risk and promote natural forest cycles.{{TOC limit|3}}

== Ignition ==
The initial ignition of a fire is usually evaluated for natural or human causes.

=== Natural ===
[[File:UC Irvine scientist James Randerson discusses new research linking ocean temperatures and fire seasons severity.ogv|thumb|UC Irvine scientist James Randerson discusses new research linking ocean temperatures and fire-season severity]]
Leading ways wildfires are naturally ignited include:<ref>{{cite web | url = http://www.nwcg.gov/pms/docs/wfprevnttrat.pdf | title = Wildfire Prevention Strategies | publisher = National Wildfire Coordinating Group | page = 17 | date = March 1998 | access-date = 3 December 2008 | url-status = dead | archive-url = https://web.archive.org/web/20081209105351/http://www.nwcg.gov/pms/docs/wfprevnttrat.pdf | archive-date = 9 December 2008 | df = dmy-all }}</ref><ref name="Scott2000">{{cite journal | doi =10.1016/S0031-0182(00)00192-9 | title = The Pre-Quaternary history of fire | date = 2000 | author = Scott, A | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 164 | issue = 1–4 | pages = 281–329 | bibcode =2000PPP...164..281S }}</ref>
* [[lightning]]
* [[volcanic eruption]]
* [[spark (fire)|spark]]s from rock falls
* [[spontaneous combustion]]

=== Human activity ===
In [[middle latitudes]], the most common human causes of wildfires are equipment generating sparks (chainsaws, grinders, mowers, etc.), [[overhead power line]]s, and [[arson]].<ref>{{cite web
| url =https://www.sandiegouniontribune.com/news/environment/story/2020-01-05/human-caused-ignitions-spark-california-worst-wildfires
| title =Human-caused ignitions spark California's worst wildfires but get little state focus
| last =Boxall
| first =Bettina
| date =5 January 2020
| website =San Diego Union-Tribune
| access-date =25 November 2020}}</ref><ref>{{Citation|title=Wildfire, forest fire, grass fire|work=SpringerReference|year=2011|publisher=Springer-Verlag|doi=10.1007/springerreference_29801}}</ref><ref>{{Cite journal|last1=Liu|first1=Zhihua|last2=Yang|first2=Jian|last3=Chang|first3=Yu|last4=Weisberg|first4=Peter J.|last5=He|first5=Hong S.|date=June 2012|title=Spatial patterns and drivers of fire occurrence and its future trend under climate change in a boreal forest of Northeast China|journal=Global Change Biology|language=en|volume=18|issue=6|pages=2041–2056|doi=10.1111/j.1365-2486.2012.02649.x|issn=1354-1013|bibcode=2012GCBio..18.2041L|s2cid=26410408}}</ref><ref>{{cite book|last1=de Rigo|first1=Daniele|last2=Libertà|first2=Giorgio|last3=Houston Durrant|first3=Tracy|last4=Artés Vivancos|first4=Tomàs|last5=San-Miguel-Ayanz|first5=Jesús|title=Forest fire danger extremes in Europe under climate change: variability and uncertainty|page=71|date=2017|publisher=Publication Office of the European Union|location=Luxembourg|isbn=978-92-79-77046-3|doi=10.2760/13180}}</ref><ref name="Krock">{{cite web|url=https://www.pbs.org/wgbh/nova/fire/world.html|title=The World on Fire|last=Krock|first=Lexi|date=June 2002|publisher=NOVA online – Public Broadcasting System (PBS)|access-date=13 July 2009|url-status=live|archive-url=https://web.archive.org/web/20091027041902/http://www.pbs.org/wgbh/nova/fire/world.html|archive-date=27 October 2009}}</ref><ref>{{Cite journal|last1=Balch|first1=Jennifer K.|last2=Bradley|first2=Bethany A.|last3=Abatzoglou|first3=John T.|last4=Nagy|first4=R. Chelsea|last5=Fusco|first5=Emily J.|last6=Mahood|first6=Adam L.|date=2017|title=Human-started wildfires expand the fire niche across the United States|journal=Proceedings of the National Academy of Sciences|language=en|volume=114|issue=11|pages=2946–2951|doi=10.1073/pnas.1617394114|pmid=28242690|issn=1091-6490|pmc=5358354|bibcode=2017PNAS..114.2946B|doi-access=free}}</ref> In the [[tropics]], farmers often practice the [[slash-and-burn]] method of clearing fields during the [[dry season]]. When thousands of farmers do this simultaneously, much of a continent can appear from orbit to be one vast blaze.<ref>{{cite web
| url =https://www.nasa.gov/image-feature/goddard/2018/agricultural-fires-seem-to-engulf-central-africa
| title =Agricultural Fires Seem to Engulf Central Africa
| date =26 June 2020
| website =NASA
| access-date =21 June 2021}}</ref><ref>{{YouTube|s1R8KdhRrDA|"Wildfires in Africa, 2021, April to December"}}</ref>

[[Coal seam fire]]s burn in the thousands around the world, such as those in [[Burning Mountain]], New South Wales; [[Centralia, Pennsylvania|Centralia]], Pennsylvania; and several [[Coal power in China#Coal mine fires|coal-sustained fires in China]]. They can also flare up unexpectedly and ignite nearby flammable material.<ref>{{cite journal|last=Krajick|first=Kevin|date=May 2005|title=Fire in the hole|url=http://www.smithsonianmag.com/travel/10013541.html|journal=Smithsonian Magazine|access-date=30 July 2009|archive-date=3 September 2010|archive-url=https://web.archive.org/web/20100903032505/http://www.smithsonianmag.com/travel/10013541.html|url-status=dead}}</ref>

== Spread ==
[[File:Wildfire near Cedar Fort, Utah.jpg|thumb|alt=Flat expanse of brown grasses and some green trees with black and some gray smoke and visible flames in the distance.|A surface fire in the western desert of [[Utah]], United States]]
[[File:Forest fire aftermath.jpg|thumb|alt=Mountainous region with blackened soil and trees due to a recent fire.|Charred landscape following a crown fire in the [[Cascade Range|North Cascades]], United States]]
[[File:Priske 24.03.2019.jpg|thumb|Forest fires visible from a distance in [[Dajti National Park]], [[Tirana]], [[Albania]]]]

The spread of wildfires varies based on the flammable material present, its vertical arrangement and moisture content, and weather conditions.<ref name="Graham, et al., iv">Graham, ''et al''., iv.</ref> Fuel arrangement and density is governed in part by [[topography]], as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be generally characterized by their fuels as follows:
* '''Ground''' fires are fed by subterranean roots, [[forest floor|duff]] and other buried [[organic matter]]. This fuel type is especially susceptible to ignition due to ''spotting'' {{See below|[[#Spotting|below]]}}. Ground fires typically burn by smoldering, and can burn slowly for days to months, such as [[Peat#Peat Fires|peat fires]] in [[Kalimantan]] and Eastern [[Sumatra]], [[Indonesia]], which resulted from a [[Mega Rice Project (Kalimantan)|riceland creation project]] that unintentionally drained and dried the peat.<ref>Graham, ''et al''., 9, 13</ref><ref>{{cite news | url = http://news.bbc.co.uk/2/hi/science/nature/4208564.stm | title = Asian peat fires add to warming | publisher = British Broadcasting Corporation (BBC) News | last = Rincon | first = Paul | date = 9 March 2005 | access-date = 9 December 2008 | url-status = live | archive-url = https://web.archive.org/web/20081219064000/http://news.bbc.co.uk/2/hi/science/nature/4208564.stm | archive-date = 19 December 2008 | df = dmy-all }}</ref><ref>{{Cite web|url=https://www.sciencenews.org/article/bogs-peatlands-fire-climate-change|title=When bogs burn, the environment takes a hit|last=Hamers|first=Laurel|date=2019-07-29|website=Science News|language=en|access-date=2019-08-15}}</ref>
* '''Crawling''' or '''surface''' fires are fueled by low-lying vegetation on the [[forest floor]] such as leaf and timber litter, debris, grass, and low-lying shrubbery.<ref>Graham, ''et al'' ., iv, 10, 14</ref> This kind of fire often burns at a relatively lower temperature than crown fires (less than {{convert|400|C|F}}) and may spread at slow rate, though steep slopes and wind can accelerate the rate of spread.<ref>{{Cite book|title=Fire on earth : an introduction|last=C.|first=Scott, Andrew|others=Bowman, D. M. J. S.; Bond, William J.; Pyne, Stephen J.; Alexander, Martin E.|isbn=978-1-119-95357-9|location=Chichester, West Sussex|oclc=854761793|year=2014}}</ref>
* '''Ladder''' fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and [[vine]]s. [[Kudzu]], [[Old World climbing fern]], and other [[invasive plant]]s that scale trees may also encourage ladder fires.<ref name="FireInitiative">{{cite web | url = http://www.tncfire.org/crosscutting_fandi.htm | title = Global Fire Initiative: Fire and Invasives | publisher = The Nature Conservancy | access-date = 3 December 2008 | url-status = dead | archive-url = https://web.archive.org/web/20090412054533/http://www.tncfire.org/crosscutting_fandi.htm | archive-date = 12 April 2009 | df = dmy-all }}</ref>
* '''Crown''', '''canopy''', or '''aerial''' fires burn suspended material at the canopy level, such as tall trees, vines, and mosses. The ignition of a crown fire, termed ''crowning'', is dependent on the density of the suspended material, canopy height, canopy continuity, sufficient surface and ladder fires, vegetation moisture content, and weather conditions during the blaze.<ref>Graham, ''et al''., iv, 8, 11, 15.</ref> Stand-replacing fires lit by humans can spread into the [[Amazon rain forest]], damaging ecosystems not particularly suited for heat or arid conditions.<ref>{{cite web|url=http://e360.yale.edu/content/feature.msp?id=2010|title=Global Commodities Boom Fuels New Assault on Amazon|last=Butler|first=Rhett|publisher=Yale School of Forestry & Environmental Studies|access-date=9 July 2009|date=19 June 2008|url-status=dead|archive-url=https://web.archive.org/web/20090411124535/http://e360.yale.edu/content/feature.msp?id=2010|archive-date=11 April 2009}}</ref>

In monsoonal areas of north Australia, surface fires can spread, including across intended firebreaks, by burning or smoldering pieces of wood or burning tufts of grass carried intentionally by large flying birds accustomed to catch prey flushed out by wildfires. Species involved in this activity are the black kite (''[[Milvus migrans]]''), whistling kite (''[[Haliastur sphenurus]]''), and brown falcon (''[[Falco berigora]]''). Local [[Aboriginal Australians|Aborigines]] have known of this behavior for a long time, including in their [[mythology]].<ref>{{cite journal | doi = 10.2993/0278-0771-37.4.700 | volume=37 | title=Intentional Fire-Spreading by "Firehawk" Raptors in Northern Australia | year=2017 | journal=Journal of Ethnobiology | page=700 | last1 = Bonta | first1 = Mark | last2 = Gosford | first2 = Robert | last3 = Eussen | first3 = Dick | last4 = Ferguson | first4 = Nathan | last5 = Loveless | first5 = Erana | last6 = Witwer | first6 = Maxwell| issue=4 | s2cid=90806420 }}</ref>

== Physical properties ==
{{anchor|Physical properties}}
[[File:Northwest Crown Fire Experiment.png|thumb|right|Experimental fire in [[Canada]]|alt=A line of trees completely engulfed in flames. Towers with instrumentation are seen just beyond the fire's reach.]]
{{See also|Combustion|Fire control|Heat wave|Firestorm}}
[[File:Comtrasts.jpg|thumb|A dirt road acted as a fire barrier in [[South Africa]]. The effects of the barrier can clearly be seen on the unburnt (left) and burnt (right) sides of the road.]]
Wildfires occur when all the necessary elements of a fire triangle come together in a susceptible area: an ignition source is brought into contact with a combustible material such as [[vegetation]] that is subjected to enough heat and has an adequate supply of oxygen from the ambient air. A high moisture content usually prevents ignition and slows propagation, because higher temperatures are needed to evaporate any water in the material and heat the material to its [[fire point]].<ref name = FireBehavior /><ref name="NIFC">{{cite web|url=http://www.nifc.gov/preved/comm_guide/wildfire/fire_4.html|title=The Science of Wildland fire|publisher=National Interagency Fire Center|access-date=21 November 2008|url-status=dead|archive-url=https://web.archive.org/web/20081105175208/http://www.nifc.gov/preved/comm_guide/wildfire/fire_4.html|archive-date=5 November 2008}}</ref> Dense forests usually provide more shade, resulting in lower ambient temperatures and greater [[humidity]], and are therefore less susceptible to wildfires.<ref name="Graham, et al., 12">Graham, ''et al''., 12.</ref> Less dense material such as grasses and leaves are easier to ignite because they contain less water than denser material such as branches and trunks.<ref name="ReferenceA">''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', 3.</ref> Plants continuously lose water by [[evapotranspiration]], but water loss is usually balanced by water absorbed from the soil, humidity, or rain.<ref>{{cite web | url = https://www.nbcnews.com/id/27148069 | title = Ashes cover areas hit by Southern Calif. fires | agency = Associated Press | publisher = NBC News | date = 15 November 2008 | access-date = 4 December 2008 | df = dmy-all }}</ref> When this balance is not maintained, plants dry out and are therefore more flammable, often as a consequence of [[drought]]s.<ref name=Structure>{{cite web | url = http://www.fs.fed.us/projects/hfi/2003/november/documents/forest-structure-wildfire.pdf | title = Influence of Forest Structure on Wildfire Behavior and the Severity of Its Effects | date = November 2003 | publisher = US Forest Service | access-date = 19 November 2008 | url-status = live | archive-url = https://web.archive.org/web/20081217125731/http://www.fs.fed.us/projects/hfi/2003/november/documents/forest-structure-wildfire.pdf | archive-date = 17 December 2008 | df = dmy-all }}</ref><ref>{{cite web | url = http://www.fema.gov/hazard/wildfire/wf_prepare.shtm | title = Prepare for a Wildfire | publisher = Federal Emergency Management Agency (FEMA) | access-date = 1 December 2008 | url-status = dead | archive-url = https://web.archive.org/web/20081029025706/https://www.fema.gov/hazard/wildfire/wf_prepare.shtm | archive-date = 29 October 2008 | df = dmy-all }}</ref>

A wildfire ''front'' is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the [[smolder]]ing transition between unburned and burned material.<ref>''Glossary of Wildland Fire Terminology'', 74.</ref> As the front approaches, the fire heats both the surrounding air and woody material through [[convection]] and [[thermal radiation]]. First, wood is dried as water is vaporized at a temperature of {{convert|100|C|F}}. Next, the [[pyrolysis]] of wood at {{convert|230|C|F|sigfig=2}} releases flammable gases. Finally, wood can smolder at {{convert|380|C|F|sigfig=2}} or, when heated sufficiently, ignite at {{convert|590|C|F|sigfig=1}}.<ref>de Sousa Costa and Sandberg, 229–230.</ref><ref>{{cite web | url = http://web.mit.edu/2.009/www/experiments/deathray/10_ArchimedesResult.html | title = Archimedes Death Ray: Idea Feasibility Testing | date = October 2005 | publisher = Massachusetts Institute of Technology (MIT) | access-date = 1 February 2009 | url-status = live | archive-url = https://web.archive.org/web/20090207164348/http://web.mit.edu/2.009/www/experiments/deathray/10_ArchimedesResult.html | archive-date = 7 February 2009 | df = dmy-all }}</ref> Even before the flames of a wildfire arrive at a particular location, [[heat transfer]] from the wildfire front warms the air to {{convert|800|C|F|sigfig=3}}, which pre-heats and dries flammable materials, causing materials to ignite faster and allowing the fire to spread faster.<ref name="ReferenceA" /><ref name=FireScars>{{cite web | url = http://www.esa.int/esaCP/SEMNJMV4QWD_Protecting_0.html | title = Satellites are tracing Europe's forest fire scars | publisher = European Space Agency | date = 27 July 2004 | access-date = 12 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20081110172926/http://www.esa.int/esaCP/SEMNJMV4QWD_Protecting_0.html | archive-date = 10 November 2008 | df = dmy-all }}</ref> High-temperature and long-duration surface wildfires may encourage [[flashover]] or ''torching'': the drying of [[canopy (ecology)|tree canopies]] and their subsequent ignition from below.<ref>Graham, ''et al''., 10–11.</ref>

{{anchor|Spot|Spotting|Spot fire}} Wildfires have a rapid ''forward rate of spread'' (FROS) when burning through dense uninterrupted fuels.<ref>{{cite web|url=http://www.flash.org/resources/files/WildfireBrochure.pdf|title=Protecting Your Home From Wildfire Damage|publisher=Florida Alliance for Safe Homes (FLASH)|access-date=3 March 2010|page=5|url-status=live|archive-url=https://web.archive.org/web/20110719000918/http://www.flash.org/resources/files/WildfireBrochure.pdf|archive-date=19 July 2011}}</ref> They can move as fast as {{convert|10.8|km/h|mph}} in forests and {{convert|22|km/h|mph}} in grasslands.<ref>Billing, 5–6</ref> Wildfires can advance tangential to the main front to form a ''flanking'' front, or burn in the opposite direction of the main front by ''backing''.<ref>Graham, ''et al''., 12</ref> They may also spread by ''jumping'' or ''spotting'' as winds and vertical [[convection]] columns carry ''firebrands'' (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as [[firebreak]]s.<ref name=underfire>{{cite magazine | url = http://ngm.nationalgeographic.com/2008/07/fire-season/shea-text.html | title = Under Fire | last = Shea | first = Neil | magazine = National Geographic | date = July 2008 | access-date = 8 December 2008 | url-status = live | archive-url = https://web.archive.org/web/20090215065522/http://ngm.nationalgeographic.com/2008/07/fire-season/shea-text.html | archive-date = 15 February 2009 | df = dmy-all }}</ref><ref>Graham, ''et al''., 16.</ref> Torching and fires in tree canopies encourage spotting, and dry ground fuels around a wildfire are especially vulnerable to ignition from firebrands.<ref>Graham, ''et al''., 9, 16.</ref> Spotting can create '''spot fires''' as hot embers and firebrands ignite fuels downwind from the fire. In [[bushfires in Australia|Australian bushfires]], spot fires are known to occur as far as {{convert|20|km|0}} from the fire front.<ref name=Kilmore-East>{{cite book
|title = Volume 1: The Kilmore East Fire
|work = 2009 Victorian Bushfires Royal Commission
|publisher = Victorian Bushfires Royal Commission, Australia
|date = July 2010
|url = http://www.royalcommission.vic.gov.au/commission-reports/final-report/volume-1/chapters/the-kilmore-east-fire
|isbn = 978-0-9807408-2-0
|access-date = 26 October 2013
|url-status = dead
|archive-url = https://web.archive.org/web/20131029190327/http://www.royalcommission.vic.gov.au/commission-reports/final-report/volume-1/chapters/the-kilmore-east-fire
|archive-date = 29 October 2013
|df = dmy-all
}}</ref>

The incidence of large, uncontained wildfires in [[North America]] has increased in recent years, significantly impacting both [[Urban area|urban]] and agriculturally-focused areas. The physical damage and health pressures left in the wake of uncontrolled fires has especially devastated farm and [[ranch]] operators in affected areas, prompting concern from the community of [[Health care|healthcare]] providers and advocates servicing this specialized occupational population.<ref>{{Cite journal|last1=Corrieri|first1=Michael L.|last2=Roy|first2=Natalie C.|last3=Rose-Davison|first3=Knesha N.|last4=Roy|first4=Chad J.|date=2019-04-03|title=Wildfire Associated Health Risks Impacting Farmers and Ranchers|journal=Journal of Agromedicine|volume=24|issue=2|pages=129–132|doi=10.1080/1059924X.2019.1581494|issn=1059-924X|pmid=30806175|doi-access=free}}</ref>

Especially large wildfires may affect air currents in their immediate vicinities by the [[stack effect]]: air rises as it is heated, and large wildfires create powerful [[updraft]]s that will [[advection|draw in]] new, cooler air from surrounding areas in [[thermal column]]s.<ref>''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', 4.</ref> Great vertical differences in temperature and humidity encourage [[pyrocumulus cloud]]s, strong winds, and [[fire whirl]]s with the force of tornadoes at speeds of more than {{convert|80|km/h|mph|sigfig=1}}.<ref>Graham, ''et al''., 16–17.</ref><ref>Olson, ''et al.'', 2</ref><ref>{{cite web | url = http://www.nwcg.gov/pms/pubs/newshelt72.pdf | title = The New Generation Fire Shelter | page = 19 | publisher = National Wildfire Coordinating Group | date = March 2003 | access-date = 16 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20090116133450/http://www.nwcg.gov/pms/pubs/newshelt72.pdf | archive-date = 16 January 2009 | df = dmy-all }}</ref> Rapid rates of spread, prolific crowning or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions.<ref>''Glossary of Wildland Fire Terminology'', 69.</ref>

The thermal heat from a wildfire can cause significant [[weathering]] of rocks and boulders. Heat can rapidly expand a boulder and [[thermal shock]] can occur, which may cause an object's structure to fail.

== Climate change effects ==
{{See also|Effects of climate change}}
[[File:Wildfire acres burned in the United States, OWID.svg|thumb|upright=1.35 | Average U.S. acreage burned annually by wildfires has almost tripled in three decades.<ref name=OWID_thru2021>{{cite web |title=Wildfire acres burned in the United States |url=https://ourworldindata.org/grapher/acres-burned-usa |website=OurWorldInData |archive-url=https://web.archive.org/web/20211012030416/https://ourworldindata.org/grapher/acres-burned-usa |archive-date=12 October 2021 |date=2021 |url-status=live}} Data published by National Interagency Coordination Center; National Interagency Fire Center. ([https://web.archive.org/web/20211011082005/https://www.nifc.gov/fire-information/statistics/wildfires archive of NIFC data])</ref>]]
[[File:2011-08-04 20 00 00 Susie Fire in the Adobe Range west of Elko Nevada.jpg|thumb|Lightning-sparked wildfires are frequent occurrences during the dry summer season in [[Nevada]].]]
[[File:Incendio en Caracas (4515878847).jpg|thumb|A wildfire in [[Venezuela]] during a [[drought]].]]

=== Increasing risks due to heat waves and droughts ===
[[Heat wave]]s, [[drought]]s, [[climate variability]] such as [[El Niño]], and regional weather patterns such as high-pressure ridges can increase the risk and alter the behavior of wildfires dramatically.<ref>{{cite web | url = http://lwf.ncdc.noaa.gov/oa/reports/billionz.html | archive-url = https://web.archive.org/web/20010915155936/http://lwf.ncdc.noaa.gov/oa/reports/billionz.html | url-status = dead | archive-date = 15 September 2001 | title = Chronological List of U.S. Billion Dollar Events | publisher = National Oceanic and Atmospheric Administration (NOAA) Satellite and Information Service | access-date = 4 February 2009 }}</ref><ref>McKenzie, ''et al.'', 893</ref><ref>{{Cite journal|last1=Provenzale|first1=Antonello|last2=Llasat|first2=Maria Carmen|last3=Montávez|first3=Juan Pedro|last4=Jerez|first4=Sonia|last5=Bedia|first5=Joaquín|last6=Rosa-Cánovas|first6=Juan José|last7=Turco|first7=Marco|date=2018-10-02|title=Exacerbated fires in Mediterranean Europe due to anthropogenic warming projected with non-stationary climate-fire models|journal=Nature Communications|language=en|volume=9|issue=1|pages=3821|doi=10.1038/s41467-018-06358-z|pmid=30279564|pmc=6168540|issn=2041-1723|bibcode=2018NatCo...9.3821T}}</ref> Years of precipitation followed by warm periods can encourage more widespread fires and longer fire seasons.<ref>Graham, ''et al''., 2</ref> Temperature affects wildfires in the same way, they dry out the load and make them more flammable.<ref>{{Cite web|last=Anuprash|date=2022-01-28|title=What Causes Wildfires? Understand The Science Here|url=https://www.techiwiki.info/post/what-causes-wildfires-understand-the-science-here|access-date=2022-02-14|website=TechiWiki|language=en}}</ref> Since the mid-1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season, or the most fire-prone time of the year,<ref>{{cite web |url= https://www.fs.fed.us/nwacfire/home/terminology.html#S|title= Fire Terminology|author=<!--Not stated-->|website=Fs.fed.us |access-date= 28 February 2019}}</ref> in the [[Western United States]].<ref>{{cite journal | doi = 10.1126/science.1128834 | date = August 2006 | author = Westerling, Al | author2 = Hidalgo, Hg | author3 = Cayan, Dr | author4 = Swetnam, Tw | title = Warming and earlier spring increase western U.S. Forest wildfire activity | volume = 313 | issue = 5789 | pages = 940–943 | issn = 0036-8075 | pmid = 16825536 | journal = Science | bibcode = 2006Sci...313..940W | doi-access = free }}</ref> [[Global warming]] may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires.<ref name="UToronto" /> A 2019 study indicates that the increase in [[California fires|fire risk in California]] may be attributable to [[Man-made climate change|human-induced climate change]].<ref>{{Cite journal|last1=Williams|first1=A. Park|last2=Abatzoglou|first2=John T.|last3=Gershunov|first3=Alexander|last4=Guzman‐Morales|first4=Janin|last5=Bishop|first5=Daniel A.|last6=Balch|first6=Jennifer K.|last7=Lettenmaier|first7=Dennis P.|author7-link=Dennis P. Lettenmaier|date=2019|title=Observed Impacts of Anthropogenic Climate Change on Wildfire in California|journal=Earth's Future|language=en|volume=7|issue=8|pages=892–910|doi=10.1029/2019EF001210|bibcode=2019EaFut...7..892W|issn=2328-4277|doi-access=free}}</ref> A study of [[alluvial]] [[sediment]] deposits going back over 8,000 years found warmer climate periods experienced severe droughts and stand-replacing fires and concluded climate was such a powerful influence on wildfire that trying to recreate presettlement forest structure is likely impossible in a warmer future.<ref>{{Cite journal|last1=Pierce|first1=Jennifer L.|last2=Meyer|first2=Grant A.|last3=Timothy Jull|first3=A. J.|date=2004-11-04|title=Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests|journal=Nature|language=en|volume=432|issue=7013|pages=87–90|doi=10.1038/nature03058|issn=0028-0836|pmid=15525985|bibcode=2004Natur.432...87P|s2cid=1452537}}</ref>

Intensity also increases during daytime hours. Burn rates of smoldering logs are up to five times greater during the day due to lower humidity, increased temperatures, and increased wind speeds.<ref>de Souza Costa and Sandberg, 228</ref> Sunlight warms the ground during the day which creates air currents that travel uphill. At night the land cools, creating air currents that travel downhill. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys.<ref>''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', 5.</ref> Fires in Europe occur frequently during the hours of 12:00&nbsp;p.m. and 2:00&nbsp;p.m.<ref>San-Miguel-Ayanz, ''et al.'', 364.</ref> Wildfire suppression operations in the United States revolve around a 24-hour ''fire day'' that begins at 10:00&nbsp;a.m. due to the predictable increase in intensity resulting from the daytime warmth.<ref>''Glossary of Wildland Fire Terminology'', 73.</ref>

In the summer of 1974–1975 (southern hemisphere), [[Australia]] suffered its worst recorded wildfire, when 15% of Australia's land mass suffered "extensive fire damage".<ref name="abs1995">{{cite web|url=https://www.abs.gov.au/Ausstats/abs@.nsf/0/6C98BB75496A5AD1CA2569DE00267E48|title=Bushfires – An Integral Part of Australia's Environment |work=1301.0 – Year Book Australia, 1995|publisher=[[Australian Bureau of Statistics]]|date=1 January 1995|author=Cheney, N. P.|access-date=14 January 2020|quote=In 1974–75 [...] in this season fires burnt over 117 million hectares or 15 per cent of the total land area of this continent.}}</ref> Fires that summer burned up an estimated {{convert|117|e6ha|e6acre km2 sqmi|abbr=off|lk=on}}.<ref name="AIDR">{{cite web |title=New South Wales, December 1974 Bushfire – New South Wales |url=https://knowledge.aidr.org.au/resources/bushfire-new-south-wales-1974/ |website=Australian Institute for Disaster Resilience |publisher=Government of Australia |access-date=13 January 2020 |archive-url=https://web.archive.org/web/20200113201506/https://knowledge.aidr.org.au/resources/bushfire-new-south-wales-1974/ |archive-date=13 January 2020 |quote=Approximately 15 per cent of Australia's physical land mass sustained extensive fire damage. This equates to roughly around 117 million ha. |url-status=live }}</ref><ref>{{cite news |last1=Cole, Brendan|title=What Caused the Wildfires in Australia? Amid Worst Blazes for a Decade, 24 People are Charged with Arson|url=https://www.newsweek.com/australia-wildfires-arson-new-south-wales-police-1480733 |access-date=14 February 2020 |work=[[Newsweek]] |date=7 January 2020 |archive-url=https://archive.today/20200214151857/https://www.newsweek.com/australia-wildfires-arson-new-south-wales-police-1480733 |archive-date=14 February 2020 |quote=In 1974, 117 million hectares of land was burnt in wildfires in central Australia.}}</ref> In Australia, the annual number of hot days (above 35&nbsp;°C) and very hot days (above 40&nbsp;°C) has increased significantly in many areas of the country since 1950. The country has always had bushfires but in 2019, the extent and ferocity of these fires increased dramatically.<ref>[https://time.com/5735660/sydney-bushfires/ As Smoke From Bushfires Chokes Sydney, Australian Prime Minister Dodges on Climate Change] {{Webarchive|url=https://web.archive.org/web/20191202070427/https://time.com/5735660/sydney-bushfires/|date=2 December 2019}}, Time 21 November 2019.</ref> For the first time catastrophic bushfire conditions were declared for Greater Sydney. New South Wales and Queensland declared a state of emergency but fires were also burning in South Australia and Western Australia.<ref>[https://www.climatecouncil.org.au/not-normal-climate-change-bushfire-web/ The facts about bushfires and climate change] {{Webarchive|url=https://web.archive.org/web/20191216072021/https://www.climatecouncil.org.au/not-normal-climate-change-bushfire-web/|date=16 December 2019}}, Climate Council, 13 November 2019</ref>

In [[2019 in climate change|2019, extreme heat and dryness]] caused massive [[Wildfires in 2019|wildfires]] in [[2019 Siberia wildfires|Siberia]], [[Deshka Landing Fire|Alaska]], [[2019 Canary Islands wildfires|Canary Islands]], [[2019–20 Australian bushfire season|Australia]], and in the [[2019 Amazon rainforest wildfires|Amazon rainforest]]. The fires in the latter were caused mainly by [[Deforestation of the Amazon rainforest|illegal logging]]. The smoke from the fires expanded on huge territory including major cities, dramatically reducing air quality.<ref>{{cite news |last1=Irfan |first1=Umair |title=Wildfires are burning around the world. The most alarming is in the Amazon rainforest. |url=https://www.vox.com/world/2019/8/20/20813786/wildfire-amazon-rainforest-brazil-siberia |access-date=23 August 2019 |agency=Vox |date=21 August 2019}}</ref>

As of August 2020, the [[Wildfires in 2020|wildfires in that year]] were 13% worse than in 2019 due primarily to [[climate change]] and [[deforestation]].<ref name="global-carbon-fire-2019">{{cite news |last1=Boyle |first1=Louise |title=Global fires are up 13% from 2019's record-breaking numbers |url=https://www.independent.co.uk/environment/climate-crisis-fires-global-heating-amazon-california-eu-a9690146.html |access-date=8 September 2020 |agency=The Independent |date=27 August 2020}}</ref> The [[Amazon rainforest]]'s existence is threatened by fires.<ref name="watching-earth-burn">{{cite news|url=https://www.nytimes.com/2020/12/28/opinion/climate-change-earth.html?action=click&module=Opinion&pgtype=Homepage |title=Opinion: Watching Earth Burn – For 10 days in September, satellites in orbit sent tragic evidence of climate change's destructive power. |first=Michael |last=Benson |newspaper=The New York Times |date=2020-12-28}}</ref><ref>{{cite news |url=https://amazonwatch.org/news/2020/1210-resisting-another-record-breaking-year-of-deforestation-and-destruction-in-the-brazilian-amazon |title=Resisting Another Record-Breaking Year of Deforestation and Destruction in the Brazilian Amazon – While Brazilian authorities deny the impact of the criminal arson, Amazon Watch and our allies exposed and challenged the growing fires and deforestation in the Amazon |date=2020-12-10 |first=Ana Paula |last=Vargas |publisher=Amazon Watch}}</ref><ref>{{cite news |title=Offensive against the Amazon: An incontrollable pandemic (commentary) |first1=Marcos |last1=Colón |first2=Luís |last2=de Camões Lima Boaventura |first3=Erik |last3=Jennings |date=2020-06-01 |url=https://news.mongabay.com/2020/06/offensive-against-the-amazon-an-incontrollable-pandemic-commentary/ }}</ref><ref>{{cite news |work=[[The Guardian]] |url=https://www.theguardian.com/world/2019/jan/02/brazil-jair-bolsonaro-amazon-rainforest-protections | title=Jair Bolsonaro launches assault on Amazon rainforest protections – Executive order transfers regulation and creation of indigenous reserves to agriculture ministry controlled by agribusiness lobby |author=Dom Phillips |date=2019-01-02}}</ref> According to Mike Barrett, Executive Director of Science and Conservation at WWF-UK, if this rainforest is destroyed "we lose the fight against climate change. There will be no going back.”<ref name="global-carbon-fire-2019" /> Record-breaking [[wildfires in 2021]] occurred in [[2021 Turkey wildfires|Turkey]], [[2021 Greece wildfires|Greece]], [[2021 California wildfires|California]] and [[2021 Russia wildfires|Russia]], thought to be linked to climate change.<ref>{{Cite news|date=2021-08-11|title=Wildfires: How are they linked to climate change?|language=en-GB|work=BBC News|url=https://www.bbc.com/news/58159451|access-date=2021-10-06}}</ref>

=== Carbon dioxide and other emissions from fires ===
Wildfires release large amounts of carbon dioxide, black and brown carbon particles, and ozone precursors such as [[volatile organic compound]]s and [[NOx|nitrogen oxides (NOx)]] into the atmosphere.<ref>{{Cite journal|last1=Spracklen|first1=Dominick V.|last2=Logan|first2=Jennifer A.|author-link2=Jennifer Logan|last3=Mickley|first3=Loretta J.|last4=Park|first4=Rokjin J.|last5=Yevich|first5=Rosemarie|last6=Westerling|first6=Anthony L.|last7=Jaffe|first7=Dan A.|date=2007|title=Wildfires drive interannual variability of organic carbon aerosol in the western U.S. in summer|journal=Geophysical Research Letters|language=en|volume=34|issue=16|doi=10.1029/2007GL030037|bibcode=2007GeoRL..3416816S|s2cid=5642896|issn=1944-8007|doi-access=free}}</ref><ref>{{Cite journal|last1=Wofsy|first1=S. C.|last2=Sachse|first2=G. W.|last3=Gregory|first3=G. L.|last4=Blake|first4=D. R.|last5=Bradshaw|first5=J. D.|last6=Sandholm|first6=S. T.|last7=Singh|first7=H. B.|last8=Barrick|first8=J. A.|last9=Harriss|first9=R. C.|last10=Talbot|first10=R. W.|last11=Shipham|first11=M. A.|last12=Browell|first12=E.V.|last13=Jacob|first13=D.J.|last14=Logan|first14=J.A.|author-link14=Jennifer Logan|date=1992|title=Atmospheric chemistry in the Arctic and subarctic: Influence of natural fires, industrial emissions, and stratospheric inputs|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92JD00622|journal=Journal of Geophysical Research: Atmospheres|language=en|volume=97|issue=D15|pages=16731–16746|doi=10.1029/92JD00622|bibcode=1992JGR....9716731W|s2cid=53612820|issn=2156-2202|access-date=26 June 2021|archive-date=26 June 2021|archive-url=https://web.archive.org/web/20210626181802/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92JD00622|url-status=dead}}</ref> These emissions affect radiation, clouds, and climate on regional and even global scales. Wildfires also emit substantial amounts of semi-volatile organic species that can partition from the gas phase to form [[secondary organic aerosol]] (SOA) over hours to days after emission. In addition, the formation of the other pollutants as the air is transported can lead to harmful exposures for populations in regions far away from the wildfires.<ref>{{Cite web|url=https://www.esrl.noaa.gov/csd/factsheets/csdWildfiresFIREX.pdf|title=The Impact of Wildfires on Climate and Air Quality|website=National Oceanic and Atmospheric Administration}}</ref> While direct emissions of harmful pollutants can affect first responders and local residents, wildfire smoke can also be transported over long distances and impact air quality across local, regional, and global scales.<ref>{{Cite web|last=US EPA|first=ORD|date=2017-03-30|title=Wildland Fire Research: Health Effects Research|url=https://www.epa.gov/air-research/wildland-fire-research-health-effects-research|access-date=2020-11-28|website=US EPA|language=en}}</ref> Whether transported smoke plumes are relevant for surface air quality depends on where they exist in the atmosphere, which in turn depends on the initial injection height of the convective smoke plume into the atmosphere. Smoke that is injected above the [[planetary boundary layer]] (PBL) may be detectable from spaceborne satellites and play a role in altering the Earth's energy budget, but would not mix down to the surface where it would impact air quality and human health. Alternatively, smoke confined to a shallow PBL (through nighttime stable stratification of the atmosphere or terrain trapping) may become particularly concentrated and problematic for surface air quality. Wildfire intensity and smoke emissions are not constant throughout the fire lifetime and tend to follow a [[diurnal cycle]] that peaks in late afternoon and early evening, and which may be reasonably approximated using a monomodal or [[Multimodal distribution|bimodal]] [[normal distribution]].<ref>{{cite journal |last1=Wiggins |first1=Elizabeth B. |last2=Soja |first2=Amber J. |last3=Gargulinski |first3=Emily |last4=Halliday |first4=Hannah S. |last5=Pierce |first5=R. Bradley |last6=Schmidt |first6=Christopher C. |last7=Nowak |first7=John B. |last8=DiGangi |first8=Joshua P. |last9=Diskin |first9=Glenn S. |last10=Katich |first10=Joseph M. |last11=Perring |first11=Anne E. |last12=Schwarz |first12=Joshua P. |last13=Anderson |first13=Bruce E. |last14=Chen |first14=Gao |last15=Crosbie |first15=Ewan C. |last16=Jordan |first16=Carolyn |last17=Robinson |first17=Claire E. |last18=Sanchez |first18=Kevin J. |last19=Shingler |first19=Taylor J. |last20=Shook |first20=Michael |last21=Thornhill |first21=Kenneth L. |last22=Winstead |first22=Edward L. |last23=Ziemba |first23=Luke D. |last24=Moore |first24=Richard H. |title=High Temporal Resolution Satellite Observations of Fire Radiative Power Reveal Link Between Fire Behavior and Aerosol and Gas Emissions |journal=Geophysical Research Letters |date=2020 |volume=47 |issue=23 |pages=e90707 |doi=10.1029/2020GL090707 |bibcode=2020GeoRL..4790707W |doi-access=free }}</ref>

Over the past century, wildfires have accounted for 20-25% of global carbon emissions, the remainder from human activities.<ref>{{cite news |url=https://www.bloomberg.com/graphics/2020-fire-emissions/ |publisher=[[Bloomberg L.P.|Bloomberg]] |title=Measuring the Carbon-Dioxide Cost of Last Year's Worldwide Wildfires |authors=Laura Millan Lombrana, Hayley Warren and Akshat Rathi |date=2020-02-10 }}</ref> Global carbon emissions from wildfires through August 2020 equaled the average annual emissions of the [[European Union]].<ref name="global-carbon-fire-2019" /> In 2020, the carbon released by California's wildfires were significantly larger than the state's other carbon emissions.<ref>{{cite news|url=https://news.mongabay.com/2020/09/off-the-chart-co2-from-california-fires-dwarf-states-fossil-fuel-emissions/ |publisher=Mongabay |title='Off the chart': CO2 from California fires dwarf state's fossil fuel emissions |first=Elizabeth Claire |last=Alberts |date=2020-09-18 }}</ref>

== Ecology ==
{{Main|Fire ecology}}
{{See also|Disturbance (ecology)|Forestry}}
[[File:Global Fires - August and February 2008.jpg|thumb|right|upright=2|alt=Two illustrations of the earth, one above the other. The seas are dark gray in color and the continents a lighter gray. Both images have red, yellow, and white markers indicating where fires occurred during the months of August (top image) and February (bottom image) of the year 2008.|Global fires during the year 2008 for the months of August (top image) and February (bottom image), as detected by the [[Moderate Resolution Imaging Spectroradiometer]] (MODIS) on NASA's [[Terra satellite]].]]

Wildfire's occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna.<ref name=":0" /> Wildfires are common in climates that are sufficiently moist to allow the growth of vegetation but feature extended dry, hot periods.<ref name="NOVA">{{cite web |author=Stephen J. Pyne |title=How Plants Use Fire (And Are Used By It) |url=https://www.pbs.org/wgbh/nova/fire/plants.html |url-status=live |archive-url=https://web.archive.org/web/20090808123751/http://www.pbs.org/wgbh/nova/fire/plants.html |archive-date=8 August 2009 |access-date=30 June 2009 |publisher=NOVA online}}</ref> Such places include the vegetated areas of Australia and [[Southeast Asia]], the [[veld]] in southern Africa, the [[fynbos]] in the Western Cape of South Africa, the forested areas of the United States and Canada, and the [[Mediterranean Basin]].

High-severity wildfire creates [[complex early seral forest]] habitat (also called “snag forest habitat”), which often has higher species richness and diversity than unburned old forest.<ref name=":1" /> Plant and animal species in most types of North American forests evolved with fire, and many of these species depend on wildfires, and particularly high-severity fires, to reproduce and grow. Fire helps to return nutrients from plant matter back to soil, the heat from fire is necessary to the germination of certain types of seeds, and the snags (dead trees) and early successional forests created by high-severity fire create habitat conditions that are beneficial to wildlife.<ref name=":1" /> Early successional forests created by high-severity fire support some of the highest levels of native biodiversity found in temperate conifer forests.<ref name=":2" /><ref>{{Cite journal|last1=Donato|first1=Daniel C.|last2=Fontaine|first2=Joseph B.|last3=Robinson|first3=W. Douglas|last4=Kauffman|first4=J. Boone|last5=Law|first5=Beverly E.|date=2009-01-01|title=Vegetation response to a short interval between high-severity wildfires in a mixed-evergreen forest|journal=Journal of Ecology|language=en|volume=97|issue=1|pages=142–154|doi=10.1111/j.1365-2745.2008.01456.x|issn=1365-2745|url=https://researchrepository.murdoch.edu.au/id/eprint/2578/|doi-access=free}}</ref> Post-fire logging has no ecological benefits and many negative impacts; the same is often true for post-fire seeding.<ref name=":5" />

Although some ecosystems rely on naturally occurring fires to regulate growth, some ecosystems suffer from too much fire, such as the [[chaparral]] in [[southern California]] and lower-elevation deserts in the American Southwest. The increased fire frequency in these ordinarily fire-dependent areas has upset natural cycles, damaged native plant communities, and encouraged the growth of non-native weeds.<ref>''Interagency Strategy for the Implementation of the Federal Wildland Fire Policy'', 3, 37.</ref><ref>Graham, ''et al''., 3.</ref><ref>{{cite journal | url = http://www.werc.usgs.gov/seki/pdfs/Future%20of%20California%20Floristics%20and%20Systematics%20Wildfire%20Th.pdf | title = Future of California floristics and systematics: wildfire threats to the California flora | author = Keeley, J.E. | journal = Madroño | volume = 42 | pages = 175–179 | date = 1995 | access-date = 26 June 2009 | url-status = live | archive-url = https://web.archive.org/web/20090507033351/http://www.werc.usgs.gov/seki/pdfs/Future%20of%20California%20Floristics%20and%20Systematics%20Wildfire%20Th.pdf | archive-date = 7 May 2009 | df = dmy-all }}</ref><ref>{{cite conference | last = Zedler | first = P.H. | title = Fire frequency in southern California shrublands: biological effects and management options | date = 1995 | book-title = Brushfires in California wildlands: ecology and resource management | editor = Keeley, J.E. | editor2 = Scott, T. | pages = 101–112 | place = Fairfield, WA | publisher = International Association of Wildland Fire}}</ref> [[Invasive species]], such as ''[[Lygodium microphyllum]]'' and ''[[Bromus tectorum]]'', can grow rapidly in areas that were damaged by fires. Because they are highly flammable, they can increase the future risk of fire, creating a [[positive feedback loop]] that increases fire frequency and further alters native vegetation communities.<ref name="FireInitiative" /><ref name="van Wagtendonk, 14">van Wagtendonk (2007), 14.</ref>

In the [[Amazon rainforest]], drought, logging, cattle ranching practices, and [[slash-and-burn]] agriculture damage fire-resistant forests and promote the growth of flammable brush, creating a cycle that encourages more burning.<ref>Nepstad, 4, 8–11</ref> Fires in the rainforest threaten its collection of diverse species and produce large amounts of CO<sub>2</sub>.<ref>{{cite web|url=http://earthobservatory.nasa.gov/Features/AmazonFireRise/|title=Amazon fires on the rise|publisher=Earth Observatory (NASA)|access-date=9 July 2009|date=5 March 2008|last=Lindsey|first=Rebecca|url-status=live|archive-url=https://web.archive.org/web/20090813154232/http://earthobservatory.nasa.gov/Features/AmazonFireRise/|archive-date=13 August 2009}}</ref> Also, fires in the rainforest, along with drought and human involvement, could damage or destroy more than half of the Amazon rainforest by 2030.<ref>Nepstad, 4</ref> Wildfires generate ash, reduce the availability of organic nutrients, and cause an increase in water runoff, eroding away other nutrients and creating [[flash flood]] conditions.<ref name="Graham, et al., iv" /><ref>{{cite web | url = http://www.ewatercrc.com.au/bushfire/background_effects.shtml | archive-url = https://web.archive.org/web/20070830055708/http://www.ewatercrc.com.au/bushfire/background_effects.shtml | url-status = dead | archive-date = 30 August 2007 | title = Bushfire and Catchments: Effects of Fire on Soils and Erosion | publisher = eWater Cooperative Research Center's | access-date = 8 January 2009 }}</ref> A 2003 wildfire in the [[North Yorkshire Moors]] burned off {{convert|2.5|km2|acre|sigfig=1|sp=us}} of [[Ericaceae|heather]] and the underlying [[peat]] layers. Afterwards, wind erosion stripped the ash and the exposed soil, revealing archaeological remains dating back to 10,000&nbsp;BC.<ref>{{cite journal|title=Fylingdales Moor a lost landscape rises from the ashes|journal=Current Archaeology |last=Refern |first=Neil |author2=Vyner, Blaise |pages=20–27 |volume=XIX |issue=226 |issn=0011-3212}}</ref> Wildfires can also have an effect on climate change, increasing the amount of carbon released into the atmosphere and inhibiting vegetation growth, which affects overall carbon uptake by plants.<ref>{{cite journal | last = Running | first = S.W. | title = Ecosystem Disturbance, Carbon and Climate | journal = Science | volume = 321 | pages = 652–653 | date = 2008 | doi = 10.1126/science.1159607 | pmid = 18669853 | issue = 5889 | s2cid = 206513681 }}</ref>

In [[tundra]] there is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals, (FRIs) that typically vary from 150 to 200 years with dryer lowland areas burning more frequently than wetter upland areas.<ref>{{cite journal |doi=10.1890/11-0387.1 |title=Variability of tundra fire regimes in Arctic Alaska: Millennial-scale patterns and ecological implications |date=2011 |last1=Higuera |first1=Philip E. |last2=Chipman |first2=Melissa L. |last3=Barnes |first3=Jennifer L. |last4=Urban |first4=Michael A. |last5=Hu |first5=Feng Sheng |journal=Ecological Applications |volume=21 |issue=8 |pages=3211–3226}}</ref>

=== Plant adaptation ===
[[File:Boreal pine forest after fire.JPG|thumb|upright=2|alt=Two photographs of the same section of a pine forest; both show blackened bark at least halfway up the trees. The first picture is noticeably lacking in surface vegetation, while the second shows small, green grasses on the forest floor.|[[Ecological succession]] after a wildfire in a [[boreal forest|boreal pine forest]] next to Hara Bog, [[Lahemaa National Park]], [[Estonia]]. The pictures were taken one and two years after the fire.]]
{{Main|Fire adaptations}}
Plants in wildfire-prone [[ecosystems]] often survive through adaptations to their local [[fire regime]]. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate [[competition]]. For example, plants of the genus ''[[Eucalyptus]]'' contain flammable oils that encourage fire and hard [[sclerophyll]] leaves to resist heat and drought, ensuring their dominance over less fire-tolerant species.<ref>{{cite web | url=http://library.csustan.edu/bsantos/section3.htm | title=Section Three: Problems, Cares, Economics, and Species | work=The Eucalyptus of California | first=Robert L. | last=Santos | publisher=California State University | date=1997 | access-date=26 June 2009 | url-status=dead | archive-url=https://web.archive.org/web/20100602175115/http://library.csustan.edu/bsantos/section3.htm | archive-date=2 June 2010 | df=dmy-all }}</ref><ref>''Fire. The Australian Experience'', 5.</ref> Dense bark, shedding lower branches, and high water content in external structures may also protect trees from rising temperatures.<ref name=NOVA /> Fire-resistant seeds and reserve [[shoot]]s that sprout after a fire encourage species preservation, as embodied by [[pioneer species]]. Smoke, charred wood, and heat can stimulate the germination of seeds in a process called ''[[serotiny]]''.<ref>{{cite journal | url = http://www.werc.usgs.gov/seki/pdfs/emissions.pdf | title = Trace gas emission in smoke-induced germination | author = Keeley, J.E. | author2 = C.J. Fotheringham | name-list-style = amp | journal = Science | volume = 276 | issue = 5316 | pages = 1248–1250 | date = 1997 | access-date = 26 June 2009 | doi = 10.1126/science.276.5316.1248 | url-status = dead | archive-url = https://web.archive.org/web/20090506235220/http://www.werc.usgs.gov/seki/pdfs/emissions.pdf | archive-date = 6 May 2009 | df = dmy-all | citeseerx = 10.1.1.3.2708 }}</ref> Exposure to smoke from burning plants promotes [[germination]] in other types of plants by inducing the production of the orange [[butenolide]].<ref name = flematti>{{cite journal | author = Flematti GR | author2 = Ghisalberti EL | author3 = Dixon KW | author4 = Trengove RD | date = 2004 | title = A compound from smoke that promotes seed germination | journal = Science | volume = 305 | issue = 5686 | page = 977 | doi = 10.1126/science.1099944 | pmid = 15247439| s2cid = 42979006 }}</ref>

Grasslands in Western [[Sabah]], Malaysian [[pine]] forests, and Indonesian ''[[Casuarina]]'' forests are believed to have resulted from previous periods of fire.<ref>Karki, 3.</ref> [[Chamise]] deadwood litter is low in water content and flammable, and the shrub quickly sprouts after a fire.<ref name=NOVA /> Cape lilies lie dormant until flames brush away the covering and then blossom almost overnight.<ref>{{cite web|last=Pyne|first=Stephen|title=How Plants Use Fire (And How They Are Used By It)|url=https://www.pbs.org/wgbh/nova/fire/plants.html|publisher=Nova|access-date=26 September 2013|url-status=live|archive-url=https://web.archive.org/web/20130912141739/http://www.pbs.org/wgbh/nova/fire/plants.html|archive-date=12 September 2013}}</ref> [[Sequoia sempervirens|Sequoia]] rely on periodic fires to reduce competition, release seeds from their [[conifer cone|cones]], and clear the soil and canopy for new growth.<ref>{{cite web |url=http://www.nps.gov/archive/seki/fire/segi.htm |title=Giant Sequoias and Fire |access-date=30 June 2009 |publisher=US National Park Service |url-status=live |archive-url=https://web.archive.org/web/20070428214757/http://www.nps.gov/archive/seki/fire/segi.htm |archive-date=28 April 2007 }}</ref> [[Caribbean Pine]] in [[Bahamian pineyards]] have adapted to and rely on low-intensity, surface fires for survival and growth. An optimum fire frequency for growth is every 3 to 10 years. Too frequent fires favor [[herbaceous plant]]s, and infrequent fires favor species typical of [[Bahamian dry forests]].<ref>{{cite web |url=http://www.nature.org/initiatives/fire/files/bahamas_assessment.pdf |title=Fire Management Assessment of the Caribbean Pine (''Pinus caribea'') Forest Ecosystems on Andros and Abaco Islands, Bahamas |work=TNC Global Fire Initiative |publisher=[[The Nature Conservancy]] |date=September 2004 |access-date=27 August 2009 |url-status=live |archive-url=https://web.archive.org/web/20081201005807/http://www.nature.org/initiatives/fire/files/bahamas_assessment.pdf |archive-date=1 December 2008 }}</ref>

=== Atmospheric effects ===
{{See also|Air pollution|Carbon cycle|Atmospheric chemistry|Haze|1997 Southeast Asian haze|2005 Malaysian haze}}
[[File:Western_fires_2020.jpg|right|upright=1.1|Wildfire smoke in [[atmosphere]] near the [[Pacific coast]] of USA in 2020|thumb]]

Most of the Earth's weather and air pollution resides in the [[troposphere]], the part of the atmosphere that extends from the surface of the planet to a height of about {{convert|10|km|mi|sigfig=1|sp=us}}. The vertical lift of a severe thunderstorm or [[pyrocumulonimbus]] can be enhanced in the area of a large wildfire, which can propel smoke, soot, and other [[Atmospheric particulate matter|particulate matter]] as high as the lower [[stratosphere]].<ref>{{cite conference | first = P.K. | last = Wang | title = The physical mechanism of injecting biomass burning materials into the stratosphere during fire-induced thunderstorms | publisher = American Geophysical Union fall meeting | date = 2003 | location = San Francisco, California }}</ref> Previously, prevailing scientific theory held that most particles in the stratosphere came from [[volcano]]es, but smoke and other wildfire emissions have been detected from the lower stratosphere.<ref>{{cite conference | bibcode = 2006AGUFM.U14A..04F | title = Smoke in the Stratosphere: What Wildfires have Taught Us About Nuclear Winter; abstract #U14A-04 | author = Fromm, M. | author2 = Stocks, B. | author3 = Servranckx, R. | author4 = Lindsey, D. | place = American Geophysical Union, Fall Meeting 2006 }}</ref> Pyrocumulus clouds can reach {{convert|6100|m|ft|sp=us}} over wildfires.<ref>Graham, ''et al''., 17</ref> Satellite observation of smoke plumes from wildfires revealed that the plumes could be traced intact for distances exceeding {{convert|1600|km|mi|sigfig=1|sp=us}}.<ref>{{cite web | url = http://ams.confex.com/ams/pdfpapers/68737.pdf | title = Meteorological Conditions Associated with the Rapid Transport of Canadian Wildfire Products into the Northeast during 5–8 July 2002 | author = John R. Scala | display-authors = etal | publisher = American Meteorological Society | access-date = 4 February 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090226080555/http://ams.confex.com/ams/pdfpapers/68737.pdf | archive-date = 26 February 2009 | df = dmy-all }}</ref> Computer-aided models such as [[CALPUFF]] may help predict the size and direction of wildfire-generated smoke plumes by using [[atmospheric dispersion modeling]].<ref>{{cite web | url = http://www.fs.fed.us/pnw/pubs/pnw_gtr379.pdf | title = User Assessment of Smoke-Dispersion Models for Wildland Biomass Burning | publisher = US Forest Service | first1 = Steve | last1 = Breyfogle | first2 = Ferguson | last2 = Sue A. | date = December 1996 | access-date = 6 February 2009 | url-status = live | archive-url = https://web.archive.org/web/20090226080555/http://www.fs.fed.us/pnw/pubs/pnw_gtr379.pdf | archive-date = 26 February 2009 | df = dmy-all }}</ref>

Wildfires can affect local atmospheric pollution,<ref>{{cite journal | last = Bravo | first = A.H. | author2 = E. R. Sosa | author3 = A. P. Sánchez | author4 = P. M. Jaimes | author5 = R. M. I. Saavedra | name-list-style = amp | title = Impact of wildfires on the air quality of Mexico City, 1992–1999 | journal = Environmental Pollution | volume = 117 | issue = 2 | pages = 243–253 | date = 2002 | doi = 10.1016/S0269-7491(01)00277-9 | pmid = 11924549
}}</ref> and release carbon in the form of carbon dioxide.<ref>{{Cite journal|last1=Dore|first1=S.|last2=Kolb|first2=T. E.|last3=Montes-Helu|first3=M.|last4=Eckert|first4=S. E.|last5=Sullivan|first5=B. W.|last6=Hungate|first6=B. A.|last7=Kaye|first7=J. P.|last8=Hart|first8=S. C.|last9=Koch|first9=G. W.|date=2010-04-01|title=Carbon and water fluxes from ponderosa pine forests disturbed by wildfire and thinning|journal=Ecological Applications|language=en|volume=20|issue=3|pages=663–683|doi=10.1890/09-0934.1|pmid=20437955|issn=1939-5582}}</ref> [[Wildland fire emissions|Wildfire emissions]] contain fine particulate matter which can cause cardiovascular and respiratory problems.<ref>{{cite web | first = R. | last = Douglass | title = Quantification of the health impacts associated with fine particulate matter due to wildfires. MS Thesis | publisher = Nicholas School of the Environment and Earth Sciences of Duke University | date = 2008 | url = http://dukespace.lib.duke.edu/dspace/bitstream/10161/495/1/MP_rld10_a_052008.pdf | url-status = dead | archive-url = https://web.archive.org/web/20100610213236/http://dukespace.lib.duke.edu/dspace/bitstream/10161/495/1/MP_rld10_a_052008.pdf | archive-date = 10 June 2010 | df = dmy-all | access-date = 1 April 2010 }}</ref> Increased fire byproducts in the troposphere can increase ozone concentration beyond safe levels.<ref>{{cite web | url = http://www.innovations-report.de/html/berichte/geowissenschaften/wildfires_ozone_pollution_violate_health_standards_120086.html | title = Wildfires Cause Ozone Pollution to Violate Health Standards | publisher = Geophysical Research Letters | date = 13 October 2008 | access-date = 4 February 2009 | author = National Center for Atmospheric Research | url-status = dead | archive-url = https://web.archive.org/web/20110927124441/http://www.innovations-report.de/html/berichte/geowissenschaften/wildfires_ozone_pollution_violate_health_standards_120086.html | archive-date = 27 September 2011 | df = dmy-all }}</ref> Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 giga[[tonne]]s (0.89 and 2.83 billion [[short ton]]s) of CO<sub>2</sub> into the atmosphere, which is between 13%–40% of the annual global carbon dioxide emissions from burning fossil fuels.<ref>{{cite journal | first = Susan E. | last = Page | author2 = Florian Siegert | author3 = John O. Rieley | author4 = Hans-Dieter V. Boehm| author5 = Adi Jaya | author6 = Suwido Limin | name-list-style = amp | title = The amount of carbon released from peat and forest fires in Indonesia during 1997 | journal= Nature | doi=10.1038/nature01131 | volume=420 | pages=61–65 | date=11 July 2002|bibcode = 2002Natur.420...61P | issue = 6911 | pmid = 12422213 | s2cid = 4379529 }}</ref><ref>{{cite journal | url = http://www.cifor.cgiar.org/publications/pdf_files/OccPapers/OP-038.pdf | publisher = Center for International Forestry Research | title = Fires in Indonesia: Causes, Costs, and Policy Implications (CIFOR Occasional Paper No. 38) | journal = Occasional Paper | last = Tacconi | first = Luca | issn = 0854-9818 | date = February 2003 | place = Bogor, Indonesia | access-date = 6 February 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090226080558/http://www.cifor.cgiar.org/publications/pdf_files/OccPapers/OP-038.pdf | archive-date = 26 February 2009 | df = dmy-all }}</ref>
In June and July 2019, fires in the Arctic emitted more than 140 megatons of carbon dioxide, according to an analysis by CAMS. To put that into perspective this amounts to the same amount of carbon emitted by 36 million cars in a year. The recent wildfires and their massive CO<sub>2</sub> emissions mean that it will be important to take them into consideration when implementing measures for reaching greenhouse gas reduction targets accorded with the [[Paris climate agreement]].<ref>{{Cite web|url=https://www.climateforesight.eu/future-earth/the-effects-of-wildfires-on-a-zero-carbon-future/|title=The Effects of Wildfires on a Zero Carbon Future|first=Francesco|last=Bassetti|date=31 August 2019|access-date=16 November 2020|archive-date=28 November 2020|archive-url=https://web.archive.org/web/20201128165555/https://www.climateforesight.eu/future-earth/the-effects-of-wildfires-on-a-zero-carbon-future/|url-status=dead}}</ref> Due to the complex oxidative chemistry occurring during the transport of wildfire smoke in the atmosphere,<ref>{{Cite journal|last1=Rana|first1=Md. Sohel|last2=Guzman|first2=Marcelo I.|date=2020-10-22|title=Oxidation of Phenolic Aldehydes by Ozone and Hydroxyl Radicals at the Air–Water Interface|journal=The Journal of Physical Chemistry A|volume=124|issue=42|pages=8822–8833|doi=10.1021/acs.jpca.0c05944|pmid=32931271|bibcode=2020JPCA..124.8822R|s2cid=221747201|issn=1089-5639|doi-access=free}}</ref> the toxicity of emissions was indicated to increase over time.<ref>{{Cite web|date=2020-10-15|title=Wildfire Smoke Toxicity Increases Over Time, Poses Public Health Risk, According to UK Chemist|url=https://uknow.uky.edu/research/wildfire-smoke-toxicity-increases-over-time-poses-public-health-risk-according-uk-chemist|access-date=2020-10-31|website=UKNow}}</ref><ref>{{Cite web|title=As smoke from forest fires ages in the atmosphere its toxicity increases|url=https://phys.org/news/2020-10-forest-ages-atmosphere-toxicity.html|access-date=2020-10-31|website=phys.org|language=en}}</ref>

Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming [[solar radiation]] during winter months by as much as 15%.<ref>{{cite conference | author = Baumgardner, D. | display-authors = etal | title = Warming of the Arctic lower stratosphere by light absorbing particles | book-title = American Geophysical Union fall meeting | date = 2003 | place = San Francisco, California}}</ref> The Amazon is estimated to hold around 90 billion tons of carbon. As of 2019, earth's atmosphere has 415 parts per million of carbon, and the destruction of the Amazon would add about 38 parts per million.<ref>{{Cite news|url=https://www.washingtonpost.com/climate-environment/what-you-need-to-know-about-the-amazon-rainforest-fires/2019/08/27/ac82b21e-c815-11e9-a4f3-c081a126de70_story.html|title=What you need to know about the Amazon rainforest fires|last=Mufson|first=Steven|newspaper=Washington post|url-status=dead|archive-url=https://web.archive.org/web/20190827182809/https://www.washingtonpost.com/climate-environment/what-you-need-to-know-about-the-amazon-rainforest-fires/2019/08/27/ac82b21e-c815-11e9-a4f3-c081a126de70_story.html|archive-date=2019-08-27}}</ref>

[[File:USA Groundwater and Soil moisture Drought Map.jpg|thumb|National map of groundwater and soil moisture in the United States. It shows the very low soil moisture associated with the 2011 fire season in [[Texas]].]]
{{wide image|Fire activity swifts creek 2007 edit.jpg|933px|Smoke trail from a fire seen while looking towards [[Dargo, Victoria|Dargo]] from [[Swifts Creek, Victoria|Swifts Creek]], Victoria, Australia, 11 January 2007|alt=Panorama of a hilly expanse featuring a large smoke trail covering more than half of the visible sky.}}

== Prevention ==
{{See also|Fire protection|}}
[[File:Healthy Hillsides - a project in Rhondda Cynon Taf between NRW and Rhondda Cynon Taf County Borough Council.webm|thumb|240px|A short video on managing and protecting the natural habitat between a town and the hillside, from the risk of fire.]]

Wildfire prevention refers to the preemptive methods aimed at reducing the risk of fires as well as lessening its severity and spread.<ref>Karki, 6.</ref> Prevention techniques aim to manage air quality, maintain ecological balances, protect resources,<ref name="van Wagtendonk, 14" /> and to affect future fires.<ref>van Wagtendonk (1996), 1156.</ref> North American firefighting policies permit naturally caused fires to burn to maintain their ecological role, so long as the risks of escape into high-value areas are mitigated.<ref>''Interagency Strategy for the Implementation of the Federal Wildland Fire Policy'', 42.</ref> However, prevention policies must consider the role that humans play in wildfires, since, for example, 95% of forest fires in Europe are related to human involvement.<ref>San-Miguel-Ayanz, ''et al.'', 361.</ref> Sources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture such as the slash-and-burn farming in Southeast Asia.<ref>Karki, 7, 11–19.</ref>

In 1937, U.S. President [[Franklin D. Roosevelt]] initiated a nationwide fire prevention campaign, highlighting the role of human carelessness in forest fires. Later posters of the program featured [[Uncle Sam]], characters from the Disney movie ''[[Bambi]]'', and the official mascot of the [[U.S. Forest Service]], [[Smokey Bear]].<ref>{{cite web | url=http://www.smokeybear.com/vault/default.asp?js=1 | title=Smokey's Journey | publisher=Smokeybear.com | access-date=26 January 2010 | url-status=live | archive-url=https://web.archive.org/web/20100306051136/http://www.smokeybear.com/vault/default.asp?js=1 | archive-date=6 March 2010 | df=dmy-all }}</ref> Reducing human-caused ignitions may be the most effective means of reducing unwanted wildfire. Alteration of fuels is commonly undertaken when attempting to affect future fire risk and behavior.<ref name="Graham, et al., iv" />

Wildfire prevention programs around the world may employ techniques such as ''wildland fire use'' (WFU) and ''prescribed or [[controlled burn]]s''.<ref>{{cite web|url=http://encarta.msn.com/dictionary_561501139/backburn.html|title=Backburn|publisher=MSN Encarta|access-date=9 July 2009|url-status=dead|archive-url=https://web.archive.org/web/20090710223715/http://encarta.msn.com/dictionary_561501139/backburn.html|archive-date=10 July 2009}}</ref><ref>{{cite journal|url=http://www.fire.uni-freiburg.de/iffn/country/gb/gb_1.htm|title=UK: The Role of Fire in the Ecology of Heathland in Southern Britain|journal=International Forest Fire News|volume=18|date=January 1998|pages=80–81|url-status=dead|archive-url=https://web.archive.org/web/20110716212702/http://www.fire.uni-freiburg.de/iffn/country/gb/gb_1.htm|archive-date=16 July 2011|access-date=9 July 2009}}</ref> ''Wildland fire use'' refers to any fire of natural causes that is monitored but allowed to burn. ''Controlled burns'' are fires ignited by government agencies under less dangerous weather conditions.<ref>{{cite web | url = http://www.smokeybear.com/prescribed-fires.asp | title = Prescribed Fires | publisher = SmokeyBear.com | access-date = 21 November 2008 | url-status = dead | archive-url = https://web.archive.org/web/20081020171425/http://www.smokeybear.com/prescribed-fires.asp | archive-date = 20 October 2008 | df = dmy-all }}</ref>
According to the [[United States Fish and Wildlife Service]], in rugged, steep, or highly inaccessible terrain where people are not threatened, wildland fire use can help avoid putting firefighters at unreasonable risk. Other objectives can include maintenance of healthy forests, rangelands, and wetlands, and support of ecosystem diversity.<ref name="US F&W Fire Mgt">{{cite web |title=Fire Management: Wildland Fire Use |url=https://www.fws.gov/fire/what_we_do/wildland_fire_use.shtml |publisher=U.S. Fish & Wildlife Service |access-date=26 September 2021}}</ref>

[[File:Prescribed burn in a Pinus nigra stand in Portugal.JPG|thumb|left|alt=A small fire on the slope of a hill. The hill features small, green shrubbery and some trees. A person in light-colored clothing in seen in the background, some distance from the flames.|A prescribed burn in a ''[[Pinus nigra]]'' stand in [[Portugal]]]]

Strategies for wildfire prevention, detection, control and suppression have varied over the years.<ref>{{cite web|title=International Experts Study Ways to Fight Wildfires|url=http://www1.voanews.com/english/news/a-13-2009-06-24-voa7-68788387.html|access-date=9 July 2009|date=24 June 2009|publisher=Voice of America (VOA) News|url-status=dead|archive-url=https://web.archive.org/web/20100107041028/http://www1.voanews.com/english/news/a-13-2009-06-24-voa7-68788387.html|archive-date=7 January 2010}}</ref> One common and inexpensive technique to reduce the risk of uncontrolled wildfires is [[controlled burn]]ing: intentionally igniting smaller less-intense fires to minimize the amount of flammable material available for a potential wildfire.<ref name="IS">''Interagency Strategy for the Implementation of the Federal Wildland Fire Policy'', entire text</ref><ref>''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', entire text</ref> Vegetation may be burned periodically to limit the accumulation of plants and other debris that may serve as fuel, while also maintaining high species diversity.<ref name=":3">''Fire. The Australian Experience'', 5–6.</ref><ref name=":4">Graham, ''et al''., 15.</ref> Jan Van Wagtendonk, a biologist at the Yellowstone Field Station, claims that Wildfire itself is "the most effective treatment for reducing a fire's rate of spread, fireline intensity, flame length, and heat per unit of area."<ref name=":7">van Wagtendonk (1996), 1164</ref> While other people claim that controlled burns and a policy of allowing some wildfires to burn is the cheapest method and an ecologically appropriate policy for many forests, they tend not to take into account the economic value of resources that are consumed by the fire, especially merchantable timber.<ref name=":5">{{Cite journal|last1=Noss|first1=Reed F.|last2=Franklin|first2=Jerry F.|last3=Baker|first3=William L.|author4-link=Tania Schoennagel|last4=Schoennagel|first4=Tania|last5=Moyle|first5=Peter B.|date=2006-11-01|title=Managing fire-prone forests in the western United States|journal=Frontiers in Ecology and the Environment|language=en|volume=4|issue=9|pages=481–487|doi=10.1890/1540-9295(2006)4[481:MFFITW]2.0.CO;2|issn=1540-9309|url=https://stars.library.ucf.edu/cgi/viewcontent.cgi?article=7478&context=facultybib2000}}</ref> Some studies conclude that while fuels may also be removed by logging, such thinning treatments may not be effective at reducing fire severity under extreme weather conditions.<ref name=":6">{{Cite journal|last1=Lydersen|first1=Jamie M.|last2=North|first2=Malcolm P.|last3=Collins|first3=Brandon M.|date=2014-09-15|title=Severity of an uncharacteristically large wildfire, the Rim Fire, in forests with relatively restored frequent fire regimes|url=https://zenodo.org/record/1258959|journal=Forest Ecology and Management|volume=328|pages=326–334|doi=10.1016/j.foreco.2014.06.005}}<!-- https://zenodo.org/record/1258959--></ref>

However, multi-agency studies conducted by the United States Department of Agriculture, the U.S. Forest Service Pacific Northwest Research Station, and the School of Forestry and Bureau of Business and Economic Research at the University of Montana, through strategic assessments of fire hazards and the potential effectiveness and costs of different hazard reduction treatments, clearly demonstrate that the most effective short- and long-term forest fire hazard reduction strategy and by far the most cost-effective method to yield long-term mitigation of forest fire risk is a comprehensive fuel reduction strategy that involves mechanical removal of overstocked trees through commercial logging and non-commercial thinning with no restrictions on the size of trees that are removed, resulting in considerably better long-term results compared to a non-commercial "thin below" operation or a commercial logging operation with diameter restrictions. Starting with a forest with a "high risk" of fire and a pre-treatment crowning index of 21, the "thin from below" practice of removing only very small trees resulted in an immediate crowning index of 43, with 29% of the post-treatment area rated "low risk" immediately and only 20% of the treatment area remaining "low risk" after 30 years, at a cost (net economic loss) of $439 per acre treated. Again starting with a forest at "high risk" of fire and a crowning index of 21, the strategy involving non-commercial thinning and commercial logging with size-restrictions resulted in an crowning index of 43 immediately post-treatment with 67% of the area considered "low risk" and 56% of the area remaining low risk after 30 years, at a cost (net economic loss) of $368 per acre treated. On the other hand, starting with a forest at "high risk" of fire and the same crowning index of 21, a comprehensive fire hazard reduction treatment strategy, without restrictions on size of trees removed, resulted in an immediate crowning index of 61 post-treatment with 69% of the treated area rated "low risk" immediately and 52% of the treated area remaining "low risk" after 30 years, with positive revenue (a net economic gain gain) of $8 per acre.<ref name=":248">{{Cite journal|last1=Fiedler|first1=Carl E.|last2=Keegan|first2=Charles E. III|last3=Woodall|first3=Christopher W.|last4=Morgan|first4=Todd A.|date=November 2004|title=A Strategic Assessment of Crown Fire Hazard in Montana: Potential Effectiveness and Costs of Hazard Reduction Treatments|url=http://www.bber.umt.edu/pubs/forest/fire/MT.pdf|journal=United States Department of Agriculture, Forest Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-622}}<!-- http://www.bber.umt.edu/pubs/forest/fire/MT.pdf--></ref><ref name=":249">{{Cite journal|last1=Fiedler|first1=Carl E.|last2=Keegan|first2=Charles E. III|last3=Robertson|first3=Stephen H.|last4=Morgan|first4=Todd A.|last5=Woodall|first5=Chris W.|last6=Chmelik|first6=John T.|date=February 11, 2002|title=A Strategic Assessment of Fire Hazard in New Mexico|url=http://www.bber.umt.edu/pubs/forest/fire/NM.pdf|journal=Joint Fire Sciences Program, in Cooperation with the U.S. Forest Service Pacific Northwest Research Station}}<!-- http://www.bber.umt.edu/pubs/forest/fire/NM.pdf--></ref>

Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a [[defensible space (fire control)|defensible space]] be maintained by clearing flammable materials within a prescribed distance from the structure.<ref name=":8">{{cite web | url = http://www.fire.ca.gov/fire_prevention/downloads/FHSZBSR_Backgrounder.pdf | title = California's Fire Hazard Severity Zone Update and Building Standards Revision | publisher = CAL FIRE | date = May 2007 | access-date = 18 December 2008 | url-status = live | archive-url = https://web.archive.org/web/20090226080558/http://www.fire.ca.gov/fire_prevention/downloads/FHSZBSR_Backgrounder.pdf | archive-date = 26 February 2009 | df = dmy-all }}</ref><ref name=":9">{{cite web | url = http://www.leginfo.ca.gov/pub/07-08/bill/sen/sb_1551-1600/sb_1595_bill_20080927_chaptered.pdf | title = California Senate Bill No. 1595, Chapter 366 | publisher = State of California | date = 27 September 2008 | access-date = 18 December 2008 | url-status = live | archive-url = https://web.archive.org/web/20120330120658/http://www.leginfo.ca.gov/pub/07-08/bill/sen/sb_1551-1600/sb_1595_bill_20080927_chaptered.pdf | archive-date = 30 March 2012 | df = dmy-all }}</ref> Communities in the [[Philippines]] also maintain [[fire line]]s {{convert|5|to|10|m|sp=us|ft}} wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather.<ref>Karki, 14.</ref> Continued residential development in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism.<ref name="Trial2">{{cite web | url = http://www.onearth.org/article/our-trial-by-fire?page=2 | title = Our Trial by Fire | last = Manning | first = Richard | publisher = onearth.org | date = 1 December 2007 | access-date = 7 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20080630035505/http://www.onearth.org/article/our-trial-by-fire?page=2 | archive-date = 30 June 2008 | df = dmy-all }}</ref> The ecological benefits of fire are often overridden by the economic and safety benefits of protecting structures and human life.<ref name="NOAA">{{cite web | url = http://www.economics.noaa.gov/?goal=ecosystems&file=events/fire/ | title = Extreme Events: Wild & Forest Fire | publisher = National Oceanic and Atmospheric Administration (NOAA) | access-date = 7 January 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090114111211/http://www.economics.noaa.gov/?goal=ecosystems&file=events%2Ffire%2F | archive-date = 14 January 2009 | df = dmy-all }}</ref>

== Detection ==
{{See also|Remote sensing}}
[[File:Drymountainlookout1930.jpg|thumb|upright|alt=A four-legged tower with a small at the top, next to two one-story buildings. The tower is four stories tall. Trees are at either side, and in the foreground, there are rocks, some vegetation, and a rough trail.|Dry Mountain Fire Lookout in the [[Ochoco National Forest]], [[Oregon]], circa 1930]]

Fast and effective detection is a key factor in wildfire fighting.<ref>San-Miguel-Ayanz, ''et al.'', 362.</ref> Early detection efforts were focused on early response, accurate results in both daytime and nighttime, and the ability to prioritize fire danger.<ref name="Integration">{{cite journal | url = http://www.westerndisastercenter.org/DOCUMENTS/PERS_PAPER.pdf | title = An Integration of Remote Sensing, GIS, and Information Distribution for Wildfire Detection and Management | journal = Photogrammetric Engineering and Remote Sensing | volume = 64 | issue = 10 | date = October 1998 | pages = 977–985 | access-date = 26 June 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090816123809/http://www.westerndisastercenter.org/DOCUMENTS/PERS_PAPER.pdf | archive-date = 16 August 2009 | df = dmy-all }}</ref> [[Fire lookout tower]]s were used in the United States in the early 20th century and fires were reported using telephones, [[carrier pigeon]]s, and [[heliograph]]s.<ref>{{cite news | url = http://archives.cbc.ca/version_print.asp?page=1&IDLan=1&IDClip=4917&IDDossier=849&IDCat=346&IDCatPa=261 | title = Radio communication keeps rangers in touch | publisher = Canadian Broadcasting Corporation (CBC) Digital Archives | date = 21 August 1957 | access-date = 6 February 2009 | url-status = live | archive-url = https://web.archive.org/web/20090813160525/http://archives.cbc.ca/version_print.asp?page=1&IDLan=1&IDClip=4917&IDDossier=849&IDCat=346&IDCatPa=261 | archive-date = 13 August 2009 | df = dmy-all }}</ref> Aerial and land photography using [[instant camera]]s were used in the 1950s until [[infrared photography|infrared scanning]] was developed for fire detection in the 1960s. However, information analysis and delivery was often delayed by limitations in communication technology. Early satellite-derived fire analyses were hand-drawn on maps at a remote site and sent via overnight mail to the [[incident commander|fire manager]]. During the [[Yellowstone fires of 1988]], a data station was established in [[West Yellowstone]], permitting the delivery of satellite-based fire information in approximately four hours.<ref name="Integration" />

Currently, public hotlines, [[fire lookout]]s in towers, and ground and aerial patrols can be used as a means of early detection of forest fires. However, accurate human observation may be limited by [[asthenopia|operator fatigue]], time of day, time of year, and geographic location. Electronic systems have gained popularity in recent years as a possible resolution to human operator error. A government report on a recent trial of three automated camera fire detection systems in Australia did, however, conclude "...detection by the camera systems was slower and less reliable than by a trained human observer". These systems may be semi- or fully automated and employ systems based on the risk area and degree of human presence, as suggested by [[Geographic information system|GIS]] data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via [[Global Positioning System]] (GPS) into a collective whole for near-realtime use by wireless [[Incident Command System|Incident Command Centers]].<ref>{{cite web | url = http://www.forestry.state.al.us/WildfireControl.aspx?bv=1&s=0 | title = Wildfire Detection and Control | publisher = Alabama Forestry Commission | access-date = 12 January 2009 | url-status = dead | archive-url = https://web.archive.org/web/20081120135635/http://www.forestry.state.al.us/WildfireControl.aspx?bv=1&s=0 | archive-date = 20 November 2008 | df = dmy-all }}</ref>

A small, high risk area that features thick vegetation, a strong human presence, or is close to a critical urban area can be monitored using a local [[sensor network]]. Detection systems may include [[wireless sensor network]]s that act as automated weather systems: detecting temperature, humidity, and smoke.<ref>{{cite web | url = http://cse.seas.wustl.edu/techreportfiles/getreport.asp?399 | archive-url = https://web.archive.org/web/20070103233730/http://cse.seas.wustl.edu/techreportfiles/getreport.asp?399 | archive-date = 3 January 2007 | format = PDF | title = Mobile Agent Middleware for Sensor Networks: An Application Case Study | date = 29 November 2004 | last = Fok | first = Chien-Liang | author2 = Roman, Gruia-Catalin | author3 = Lu, Chenyang | name-list-style = amp | publisher = Washington University in St. Louis | access-date = 15 January 2009}}</ref><ref>{{Cite book | title = Wireless Sensor Network Based System for Fire Endangered Areas | date = July 2005 | last = Chaczko | first = Z. | author2 = Ahmad, F. | journal = Third International Conference on Information Technology and Applications | volume = 2 | issue = 4–7 | pages = 203–207 | doi = 10.1109/ICITA.2005.313 | isbn = 978-0-7695-2316-3 | s2cid = 14472324 }}</ref><ref>{{cite web | url = http://firecenter.umt.edu/index.php/project/Wireless-Weather-Sensor-Networks-for-Fire-Management/ID/461d72ad/fuseaction/whatWeDo.projectDetail.htm | title = Wireless Weather Sensor Networks for Fire Management | publisher = University of Montana – Missoula | access-date = 19 January 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090404124819/http://firecenter.umt.edu/index.php/project/Wireless-Weather-Sensor-Networks-for-Fire-Management/ID/461d72ad/fuseaction/whatWeDo.projectDetail.htm | archive-date = 4 April 2009 | df = dmy-all }}</ref><ref>{{cite web |url=http://www.libelium.com/libeliumworld/articles/101031032811 |title=Detecting Forest Fires using Wireless Sensor Networks with Waspmote |publisher=Libelium Comunicaciones Distribuidas S.L. |first=Javier |last=Solobera |date=9 April 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100417133344/http://www.libelium.com/libeliumworld/articles/101031032811 |archive-date=17 April 2010 |access-date=5 July 2010 }}</ref> These may be battery-powered, solar-powered, or ''tree-rechargeable'': able to recharge their battery systems using the small electrical currents in plant material.<ref>{{cite web | url = http://web.mit.edu/newsoffice/2008/trees-0923.html | title = Preventing forest fires with tree power | date = 23 September 2008 | access-date = 15 January 2009 | last = Thomson | first = Elizabeth A. | publisher = Massachusetts Institute of Technology (MIT) News | url-status = live | archive-url = https://web.archive.org/web/20081229071819/http://web.mit.edu/newsoffice/2008/trees-0923.html | archive-date = 29 December 2008 | df = dmy-all }}</ref> Larger, medium-risk areas can be monitored by scanning towers that incorporate fixed cameras and sensors to detect smoke or additional factors such as the infrared signature of carbon dioxide produced by fires. Additional capabilities such as [[night vision]], brightness detection, and color change detection may also be incorporated into sensor arrays.<ref>"Evaluation of three wildfire smoke detection systems", 6</ref><ref>{{cite web | url = http://advancement.sdsu.edu/marcomm/news/releases/spring2005/pr062305.html | archive-url = https://web.archive.org/web/20060901120511/http://advancement.sdsu.edu/marcomm/news/releases/spring2005/pr062305.html | archive-date = 1 September 2006 | title = SDSU Tests New Wildfire-Detection Technology | date = 23 June 2005 | place = San Diego, CA | publisher = San Diego State University | access-date = 12 January 2009}}</ref><ref>San-Miguel-Ayanz, ''et al.'', 366–369, 373–375.</ref>

[[File:Wildfires Balkans July 2007-NASA.jpg|thumb|upright=1.1|alt=A satellite view of the Balkans and Greece. Clouds and smoke trails are seen above the Balkans and trailing south into the Ionian Sea.|Wildfires across the [[Balkans]] in late July 2007 ([[MODIS]] image)]]
[[File:Global map of fire alerts April 13, 2021 screen dump from Global Forest Watch website.png|thumb|upright=1.35|Global map of fire alerts on April 13, 2021. Available from [[Global Forest Watch]]. [https://www.globalforestwatch.org/map/?map=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&menu=eyJtZW51U2VjdGlvbiI6IiIsImRhdGFzZXRDYXRlZ29yeSI6IiJ9 <u>Live updates</u>]. ]]
Satellite and aerial monitoring through the use of planes, helicopter, or UAVs can provide a wider view and may be sufficient to monitor very large, low risk areas. These more sophisticated systems employ GPS and aircraft-mounted infrared or high-resolution visible cameras to identify and target wildfires.<ref>{{cite web | author = Rochester Institute of Technology | url = https://www.sciencedaily.com/releases/2003/04/030410072055.htm | title = New Wildfire-detection Research Will Pinpoint Small Fires From 10,000 feet | website = ScienceDaily | date = 4 October 2003 | access-date = 12 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20080605223918/https://www.sciencedaily.com/releases/2003/04/030410072055.htm | archive-date = 5 June 2008 | df = dmy-all }}</ref><ref>{{cite web | url = http://www.esa.int/esaLP/SEMEAE0CYTE_index_0.html | title = Airborne campaign tests new instrumentation for wildfire detection | date = 11 October 2006 | publisher = European Space Agency | access-date = 12 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20090813163219/http://www.esa.int/esaLP/SEMEAE0CYTE_index_0.html | archive-date = 13 August 2009 | df = dmy-all }}</ref> Satellite-mounted sensors such as [[Envisat]]'s [[AATSR|Advanced Along Track Scanning Radiometer]] and [[European Remote-Sensing Satellite]]'s Along-Track Scanning Radiometer can measure infrared radiation emitted by fires, identifying hot spots greater than {{convert|39|C|F}}.<ref>{{cite web | url = http://www.esa.int/esaCP/SEMRBH9ATME_Protecting_0.html | title = World fire maps now available online in near-real time | publisher = European Space Agency | date = 24 May 2006 | access-date = 12 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20090813163601/http://www.esa.int/esaCP/SEMRBH9ATME_Protecting_0.html | archive-date = 13 August 2009 | df = dmy-all }}</ref><ref>{{cite web | url = http://www.esa.int/esaEO/SEMEKMZBYTE_index_0.html | title = Earth from Space: California's 'Esperanza' fire | date = 11 March 2006 | publisher = European Space Agency | access-date = 12 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20081110113923/http://www.esa.int/esaEO/SEMEKMZBYTE_index_0.html | archive-date = 10 November 2008 | df = dmy-all }}</ref> The [[National Oceanic and Atmospheric Administration]]'s [[Hazard Mapping System]] combines remote-sensing data from satellite sources such as [[Geostationary Operational Environmental Satellite]] (GOES), [[Moderate-Resolution Imaging Spectroradiometer]] (MODIS), and [[Advanced Very High Resolution Radiometer]] (AVHRR) for detection of fire and smoke plume locations.<ref>{{cite web | url = http://www.ssd.noaa.gov/PS/FIRE/hms.html | publisher = National Oceanic and Atmospheric Administration (NOAA) Satellite and Information Service | title = Hazard Mapping System Fire and Smoke Product | access-date = 15 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20090114044127/http://www.ssd.noaa.gov/PS/FIRE/hms.html | archive-date = 14 January 2009 | df = dmy-all }}</ref><ref name="Swarm">{{cite journal | url = http://www3.interscience.wiley.com/journal/119817008/abstract | archive-url = https://wayback.archive-it.org/all/20170525100110/http://onlinelibrary.wiley.com/doi/10.1002/dac.937/abstract | url-status = dead | archive-date = 25 May 2017 | title = A probabilistic zonal approach for swarm-inspired wildfire detection using sensor networks | last = Ramachandran | first = Chandrasekar | author2 = Misra, Sudip | author3 = Obaidat, Mohammad S. | author3-link = Mohammad S. Obaidat | name-list-style = amp | journal = Int. J. Commun. Syst. | volume = 21 | issue = 10 | pages = 1047–1073 | date = 9 June 2008 | doi = 10.1002/dac.937 | s2cid = 30988736 }}</ref> However, satellite detection is prone to offset errors, anywhere from {{convert|2|to|3|km|mi|sigfig=1|sp=us}} for MODIS and AVHRR data and up to {{convert|12|km|mi|sp=us}} for GOES data.<ref>{{cite web | url = https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050180316_2005176776.pdf | title = Automated Wildfire Detection Through Artificial Neural Networks | last = Miller | first = Jerry | author2 = Borne, Kirk | author3 = Thomas, Brian | author4 = Huang Zhenping | author5 = Chi, Yuechen | name-list-style = amp | publisher = NASA | access-date = 15 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20100522013312/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050180316_2005176776.pdf | archive-date = 22 May 2010 | df = dmy-all }}</ref> Satellites in geostationary orbits may become disabled, and satellites in polar orbits are often limited by their short window of observation time. Cloud cover and image resolution may also limit the effectiveness of satellite imagery.<ref>{{cite journal | title = Forest fire detection system based on a ZigBee wireless sensor network | date = September 2008 | doi = 10.1007/s11461-008-0054-3 | pages = 369–374 | volume = 3 | issue = 3 | journal = Frontiers of Forestry in China | last = Zhang | first = Junguo | author2 = Li, Wenbin | author3 = Han, Ning | author4 = Kan, Jiangming | s2cid = 76650011 | name-list-style = amp }}</ref> [[Global Forest Watch]] provides detailed daily updates on fire alerts. These are sourced from [https://earthdata.nasa.gov/earth-observation-data/near-real-time/firms/viirs-i-band-active-fire-data NASA FIRMS]. “VIIRS Active Fires.”

In 2015 a new fire detection tool is in operation at the [[United States Department of Agriculture|U.S. Department of Agriculture]] (USDA) [[United States Forest Service|Forest Service]] (USFS) which uses data from the [[Suomi NPP|Suomi National Polar-orbiting Partnership]] (NPP) satellite to detect smaller fires in more detail than previous space-based products. The high-resolution data is used with a computer model to predict how a fire will change direction based on weather and land conditions. The active fire detection product using data from Suomi NPP's [[Visible Infrared Imaging Radiometer Suite]] (VIIRS) increases the resolution of fire observations to 1,230 feet (375 meters). Previous NASA satellite data products available since the early 2000s observed fires at 3,280 foot (1 kilometer) resolution. The data is one of the intelligence tools used by the USFS and Department of Interior agencies across the United States to guide resource allocation and strategic fire management decisions. The enhanced VIIRS fire product enables detection every 12 hours or less of much smaller fires and provides more detail and consistent tracking of fire lines during long-duration wildfires – capabilities critical for early warning systems and support of routine mapping of fire progression. Active fire locations are available to users within minutes from the satellite overpass through data processing facilities at the USFS Remote Sensing Applications Center, which uses technologies developed by the NASA Goddard Space Flight Center Direct Readout Laboratory in Greenbelt, Maryland. The model uses data on weather conditions and the land surrounding an active fire to predict 12–18 hours in advance whether a blaze will shift direction. The state of Colorado decided to incorporate the weather-fire model in its firefighting efforts beginning with the 2016 fire season.

In 2014, an international campaign was organized in South Africa's Kruger National Park to validate fire detection products including the new VIIRS active fire data. In advance of that campaign, the Meraka Institute of the Council for Scientific and Industrial Research in Pretoria, South Africa, an early adopter of the VIIRS 375&nbsp;m fire product, put it to use during several large wildfires in Kruger.

The demand for timely, high-quality fire information has increased in recent years. Wildfires in the United States burn an average of 7 million acres of land each year. For the last 10 years, the USFS and Department of Interior have spent a combined average of about $2–4 billion annually on wildfire suppression.

== Suppression ==
{{Main|Wildfire suppression}}

{{See also|Firefighting}}
[[File:RIAN archive 733844 Forest fires ravaging near Novovoronezh Nuclear Power Plant.jpg|thumb|A Russian firefighter extinguishing a wildfire]]
Wildfire suppression depends on the technologies available in the area in which the wildfire occurs. In less developed nations the techniques used can be as simple as throwing sand or beating the fire with sticks or palm fronds.<ref>Karki, 16</ref> In more advanced nations, the suppression methods vary due to increased technological capacity. [[Silver iodide]] can be used to encourage snow fall,<ref>{{cite news |url=http://origin.foxnews.com/story/0,2933,195969,00.html |title=China Makes Snow to Extinguish Forest Fire |publisher=FOXNews.com |access-date=10 July 2009 |date=18 May 2006 |url-status=dead |archive-url=https://web.archive.org/web/20090813173448/http://origin.foxnews.com/story/0,2933,195969,00.html |archive-date=13 August 2009 }}</ref> while [[fire retardant]]s and water can be dropped onto fires by [[unmanned aerial vehicle]]s, [[airtanker|planes]], and [[helitack|helicopters]].<ref>{{cite web |url=http://geo.arc.nasa.gov/sge/WRAP//projects/docs/ISRSE_PAPER_2003.PDF |access-date=21 July 2009 |title=Disaster Management Applications – Fire |first=Vincent G. |last=Ambrosia |publisher=NASA-Ames Research Center |date=2003 |url-status=dead |archive-url=https://web.archive.org/web/20090724081427/http://geo.arc.nasa.gov/sge/WRAP/projects/docs/ISRSE_PAPER_2003.PDF |archive-date=24 July 2009 }}</ref><ref>Plucinski, ''et al.'', 6</ref> Complete fire suppression is no longer an expectation, but the majority of wildfires are often extinguished before they grow out of control. While more than 99% of the 10,000 new wildfires each year are contained, escaped wildfires under extreme weather conditions are difficult to suppress without a change in the weather. Wildfires in Canada and the US burn an average of {{convert|54500|km2|acre|sigfig=2|sp=us}} per year.<ref>{{cite news|url=http://www.cbc.ca/canada/story/2009/06/17/f-forest-fires.html |title=Fighting fire in the forest |publisher=CBS News |date=17 June 2009 |access-date=26 June 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090619212242/http://www.cbc.ca/canada/story/2009/06/17/f-forest-fires.html |archive-date=19 June 2009 }}</ref><ref>{{cite web | url = http://www.ncdc.noaa.gov/sotc/?report=fire&year=2008&month=13 | title = Climate of 2008 Wildfire Season Summary | publisher = National Climatic Data Center | date = 11 December 2008 | access-date = 7 January 2009 | url-status = live | archive-url = https://web.archive.org/web/20151023095354/http://www.ncdc.noaa.gov/sotc/?report=fire&year=2008&month=13 | archive-date = 23 October 2015 | df = dmy-all }}</ref>

Above all, fighting wildfires can become deadly. A wildfire's burning front may also change direction unexpectedly and jump across fire breaks. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire, which can make fires particularly dangerous. For example, during the 1949 [[Mann Gulch fire]] in [[Montana]], United States, thirteen [[smokejumper]]s died when they lost their communication links, became disoriented, and were overtaken by the fire.<ref>{{cite web | url = http://www.fs.fed.us/rm/pubs_int/int_gtr299/ | title = General Technical Report INT-GTR-299 – Mann Gulch Fire: A Race That Couldn't Be Won | publisher = United States Department of Agriculture, Forest Service, Intermountain Research Station | date = May 1993 | last = Rothermel | first = Richard C. | access-date = 26 June 2009 | url-status = live | archive-url = https://web.archive.org/web/20090813122911/http://www.fs.fed.us/rm/pubs_int/int_gtr299/ | archive-date = 13 August 2009 | df = dmy-all }}</ref> In the Australian [[February 2009 Victorian bushfires]], at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.<ref name="homeslost">{{cite web|url=http://www.parliament.nsw.gov.au/prod/PARLMENT/hansart.nsf/V3Key/LA20090313005|title=Victorian Bushfires|date=13 March 2009|publisher=New South Wales Government|work=Parliament of New South Wales|access-date=26 January 2010|url-status=live|archive-url=https://web.archive.org/web/20100227231203/http://www.parliament.nsw.gov.au/prod/PARLMENT/hansart.nsf/V3Key/LA20090313005|archive-date=27 February 2010}}</ref>

=== Costs of wildfire suppression ===
The suppression of wild fires takes up a large amount of a country's [[gross domestic product]] which directly affects the country's economy.<ref name="ellison">{{cite journal|last=Ellison|first=A|author2=Evers, C.|author3=Moseley, C.|author4=Nielsen-Pincus, M.|year=2012|title=Forest service spending on large wildfires in the West|url=http://ewp.uoregon.edu/sites/ewp.uoregon.edu/files/WP_41.pdf|journal=Ecosystem Workforce Program|volume=41|pages=1–16}}</ref> While costs vary wildly from year to year, depending on the severity of each fire season, in the United States, local, state, federal and tribal agencies collectively spend tens of billions of dollars annually to suppress wildfires. In the United States, it was reported that approximately $6 billion was spent between 2004–2008 to suppress wildfires in the country.<ref name="ellison" /> In California, the U.S. Forest Service spends about $200 million per year to suppress 98% of wildfires and up to $1 billion to suppress the other 2% of fires that escape initial attack and become large.<ref>{{Cite web|title=Region 5 – Land & Resource Management|url=http://www.fs.usda.gov/detail/r5/landmanagement/?cid=stelprdb5412095|url-status=live|archive-url=https://web.archive.org/web/20160823005834/http://www.fs.usda.gov/detail/r5/landmanagement/?cid=stelprdb5412095|archive-date=23 August 2016|access-date=2016-08-22|website=www.fs.usda.gov}}</ref>

=== Wildland firefighting safety ===
[[File:Wildfire fighter.jpg|thumb|Wildfire fighters cutting down a tree using a chainsaw]]
[[File:Wildland Firefighter.jpg|thumb|upright|Wildland firefighter working a brush fire in [[Hopkinton, New Hampshire|Hopkinton]], New Hampshire]]
Wildland fire fighters face several life-threatening hazards including [[heat stress]], [[fatigue (safety)|fatigue]], [[smoke]] and [[dust]], as well as the risk of other injuries such as [[burn]]s, [[wound|cuts]] and [[Abrasion (medical)|scrapes]], [[animal bites]], and even [[rhabdomyolysis]].<ref name="niosh-blog">{{cite web|title=Wildland Fire Fighting Safety and Health|url=http://blogs.cdc.gov/niosh-science-blog/2012/07/wildlandfire/|work=NIOSH Science Blog|publisher=National Institute of Occupational Safety and Health|access-date=6 August 2012|first=Corey|last=Campbell|author2=Liz Dalsey|url-status=live|archive-url=https://web.archive.org/web/20120809023909/http://blogs.cdc.gov/niosh-science-blog/2012/07/wildlandfire/|archive-date=9 August 2012}}</ref><ref name="Hot Tips from NIOSH">{{cite web|title=Wildland Fire Fighting: Hot Tips to Stay Safe and Healthy|url=https://www.cdc.gov/NIOSH/docs/2013-158/pdfs/2013-158.pdf|publisher=National Institute for Occupational Safety and Health|access-date=21 March 2014|url-status=live|archive-url=https://web.archive.org/web/20140322030104/http://www.cdc.gov/NIOSH/docs/2013-158/pdfs/2013-158.pdf|archive-date=22 March 2014}}</ref> Between 2000–2016, more than 350&nbsp;wildland firefighters died on-duty.<ref name="NIOSH Wildland Firefighting default page">{{Cite web |url=https://www.cdc.gov/niosh/topics/firefighting/default.html |title=CDC – Fighting Wildfires – NIOSH Workplace Safety and Health Topic |date=31 May 2018 |website=www.cdc.gov |publisher=[[National Institute for Occupational Safety and Health]] |language=en-us |access-date=2018-11-27 |quote=Between 2000–2016, based on data compiled in the NIOSH Wildland Fire Fighter On-Duty Death Surveillance System from three data sources, over 350 on-duty WFF fatalities occurred.}}</ref>

Especially in hot weather conditions, fires present the risk of heat stress, which can entail feeling heat, fatigue, weakness, vertigo, headache, or nausea. Heat stress can progress into heat strain, which entails physiological changes such as increased heart rate and core body temperature. This can lead to heat-related illnesses, such as heat rash, cramps, exhaustion or [[heat stroke]]. Various factors can contribute to the risks posed by heat stress, including strenuous work, personal risk factors such as age and [[Physical fitness|fitness]], dehydration, sleep deprivation, and burdensome [[personal protective equipment]]. Rest, cool water, and occasional breaks are crucial to mitigating the effects of heat stress.<ref name="niosh-blog" />

Smoke, ash, and debris can also pose serious respiratory hazards to wildland firefighters. The smoke and dust from wildfires can contain gases such as [[carbon monoxide]], [[sulfur dioxide]] and [[formaldehyde]], as well as [[Atmospheric particulate matter|particulates]] such as [[Wood ash|ash]] and [[silica]]. To reduce smoke exposure, wildfire fighting crews should, whenever possible, rotate firefighters through areas of heavy smoke, avoid downwind firefighting, use equipment rather than people in holding areas, and minimize mop-up. Camps and command posts should also be located upwind of wildfires. Protective clothing and equipment can also help minimize exposure to smoke and ash.<ref name="niosh-blog" />

Firefighters are also at risk of cardiac events including strokes and heart attacks. Firefighters should maintain good physical fitness. Fitness programs, medical screening and examination programs which include stress tests can minimize the risks of firefighting cardiac problems.<ref name="niosh-blog" /> Other injury hazards wildland firefighters face include slips, trips, falls, burns, scrapes, and cuts from tools and equipment, being struck by trees, vehicles, or other objects, plant hazards such as thorns and poison ivy, snake and animal bites, vehicle crashes, electrocution from power lines or lightning storms, and unstable building structures.<ref name="niosh-blog" />

==== Firefighter safety zone guidelines ====
The U.S. Forest Service publishes guidelines for the minimum distance a firefighter should be from a flame.<ref>{{Cite web|url=https://www.fs.fed.us/rm/pubs_other/rmrs_2009_butler_b001.pdf|title=&#124; US Forest Service &#124; Efforts To Update Firefighter Safety Zone Guidelines|access-date=10 January 2021}}</ref> As stated in the National Wildfire Coordinating Group's [https://www.nwcg.gov/sites/default/files/publications/pms461.pdf Incident Response Pocket Guide]: "A safety zone is an area where a firefighter can survive without a [[fire shelter]]" and should be "...at least four times the maximum continuous flame height."<ref>{{Cite web |date=January 2022 |title=NWCG Incident Response Pocket Guide |url=https://www.nwcg.gov/sites/default/files/publications/pms461.pdf}}</ref> However this figure only takes into account the effects of radiant heat and does not consider topography nor wind.

Safety Zones can natural features such as rock screes, meadows, and river bars; or human-made features such a parking lots or areas that have been cleared of vegetation through mechanical means.

=== Fire retardants ===
Fire retardants are used to slow wildfires by inhibiting combustion. They are aqueous solutions of ammonium phosphates and ammonium sulfates, as well as thickening agents.<ref>{{cite journal |author=A. Agueda |author2=E. Pastor |author3=E. Planas |year=2008|title=Different scales for studying the effectiveness of long-term forest fire retardants|journal=Progress in Energy and Combustion Science|volume=24|issue=6|pages=782–796|doi=10.1016/j.pecs.2008.06.001}}</ref> The decision to apply retardant depends on the magnitude, location and intensity of the wildfire. In certain instances, fire retardant may also be applied as a precautionary fire defense measure.<ref name="coloradoan.com">{{cite web|author=Magill, B.|title=Officials: Fire slurry poses little threat|work=Coloradoan.com|url=http://www.coloradoan.com/article/20120706/NEWS01/307060035/Officials-Fire-slurry-poses-little-threat}}</ref>

Typical fire retardants contain the same agents as fertilizers. Fire retardants may also affect water quality through leaching, eutrophication, or misapplication. Fire retardant's effects on drinking water remain inconclusive.<ref name="minesnewsroom.com">{{cite journal |author=Boerner, C. |author2=Coday B. |author3=Noble, J. |author4=Roa, P. |author5=Roux V. |author6=Rucker K. |author7=Wing, A. |year=2012 |title=Impact of wildfire in Clear Creek Watershed of the city of Golden's drinking water supply |publisher=Colorado School of Mines |url=http://minesnewsroom.com/sites/default/files/wysiwyg-editor/Impacts%20of%20wildfire%20on%20Golden%27s%20drinking%20water-1.pdf |url-status=live |archive-url=https://web.archive.org/web/20121112021046/http://minesnewsroom.com/sites/default/files/wysiwyg-editor/Impacts%20of%20wildfire%20on%20Golden%27s%20drinking%20water-1.pdf |archive-date=12 November 2012 }}</ref> Dilution factors, including water body size, rainfall, and water flow rates lessen the concentration and potency of fire retardant.<ref name="coloradoan.com" /> Wildfire debris (ash and sediment) clog rivers and reservoirs increasing the risk for floods and erosion that ultimately slow and/or damage water treatment systems.<ref name="minesnewsroom.com" /><ref>{{cite web|author=Eichenseher, T.|year=2012|title=Colorado Wildfires Threaten Water Supplies|work=National Geographic Daily News|url=http://news.nationalgeographic.com/news/2012/07/120703/colorado-wildfires-waldo-high-park-hayman-threaten-water-supplies/|url-status=live|archive-url=https://web.archive.org/web/20120710084010/http://news.nationalgeographic.com/news/2012/07/120703/colorado-wildfires-waldo-high-park-hayman-threaten-water-supplies/|archive-date=10 July 2012}}</ref> There is continued concern of fire retardant effects on land, water, wildlife habitats, and watershed quality, additional research is needed. However, on the positive side, fire retardant (specifically its nitrogen and phosphorus components) has been shown to have a fertilizing effect on nutrient-deprived soils and thus creates a temporary increase in vegetation.<ref name="coloradoan.com" />

The current USDA procedure maintains that the aerial application of fire retardant in the United States must clear waterways by a minimum of 300 feet to safeguard effects of retardant runoff. Aerial uses of fire retardants are required to avoid application near waterways and endangered species (plant and animal habitats). After any incident of fire retardant misapplication, the U.S. Forest Service requires reporting and assessment impacts be made to determine a mitigation, remediation, and/or restrictions on future retardant uses in that area.

=== Modeling ===
[[File:Propagation model wildfire (English).svg|right|thumb|upright=1.1|alt=A dark region shaped like a shield with a pointed bottom. An arrow and the text "propagation axis (wind)" indicates a bottom-to-top direction up the body of the shield shape. The shape's pointed bottom is labeled "fire starter". Around the shield shape's top and thinning towards its sides, a yellow-orange region is labeled "left front", "right front", and (at the top) "head of the fire".|Fire Propagation Model]]
{{Main|Wildfire modeling}}

[[File:ACTbushfire03.jpg|thumb|upright=1.1|[[Canberra bushfires|2003 Canberra firestorm]]]]

Wildfire modeling is concerned with [[numerical simulation]] of wildfires to comprehend and predict fire behavior.<ref>{{cite web|title=Prometheus|url=http://firegrowthmodel.ca/|url-status=live|archive-url=https://web.archive.org/web/20110203061723/http://firegrowthmodel.ca/|archive-date=3 February 2011|access-date=1 January 2009|publisher=Tymstra, C.; Bryce, R.W.; Wotton, B.M.; Armitage, O.B. 2009. Development and structure of Prometheus: the Canadian wildland fire growth simulation model. Inf. Rep. NOR-X-417. Nat. Resour. Can., Can. For. Serv., North. For. Cent., Edmonton, AB.|df=dmy-all}}</ref><ref>{{cite web|title=FARSITE|url=http://www.firemodels.org/content/view/112/143/|archive-url=https://web.archive.org/web/20080215083312/http://www.firemodels.org/content/view/112/143/|archive-date=15 February 2008|access-date=1 July 2009|publisher=FireModels.org – Fire Behavior and Danger Software, Missoula Fire Sciences Laboratory}}</ref> Wildfire modeling aims to aid wildfire suppression, increase the safety of firefighters and the public, and minimize damage. Using [[computational science]], wildfire modeling involves the statistical analysis of past fire events to predict spotting risks and front behavior. Various wildfire propagation models have been proposed in the past, including simple ellipses and egg- and fan-shaped models. Early attempts to determine wildfire behavior assumed terrain and vegetation uniformity. However, the exact behavior of a wildfire's front is dependent on a variety of factors, including wind speed and slope steepness. Modern growth models utilize a combination of past ellipsoidal descriptions and [[Huygens' Principle]] to simulate fire growth as a continuously expanding polygon.<ref>G.D. Richards, "An Elliptical Growth Model of Forest Fire Fronts and Its Numerical Solution", Int. J. Numer. Meth. Eng.. 30:1163–1179, 1990.</ref><ref>Finney, 1–3.</ref> [[Extreme value theory]] may also be used to predict the size of large wildfires. However, large fires that exceed suppression capabilities are often regarded as statistical outliers in standard analyses, even though fire policies are more influenced by large wildfires than by small fires.<ref name="Alvarado, et al., 66-68">Alvarado, ''et al''., 66–68</ref>

== Human risk and exposure ==

Wildfire risk is the chance that a wildfire will start in or reach a particular area and the potential loss of human values if it does. Risk is dependent on variable factors such as human activities, weather patterns, availability of wildfire fuels, and the availability or lack of resources to suppress a fire.<ref>{{cite web|publisher=Oregon State University|title=About Oregon wildfire risk|access-date=9 July 2012|url=http://oeapp.oregonexplorer.info/Wildfire/topics/topics.aspx?Res=16142|url-status=dead|archive-url=https://archive.today/20130218072405/http://oeapp.oregonexplorer.info/Wildfire/topics/topics.aspx?Res=16142|archive-date=18 February 2013}}</ref> Wildfires have continually been a threat to human populations. However, human-induced geographical and climatic changes are exposing populations more frequently to wildfires and increasing wildfire risk. It is speculated that the increase in wildfires arises from a century of wildfire suppression coupled with the rapid expansion of human developments into fire-prone wildlands.<ref>{{cite web |url=http://www.fs.fed.us/psw/publications/documents/psw_gtr208en/psw_gtr208en_505-512_haines.pdf |title=The National Wildfire Mitigation Programs Database: State, County, and Local Efforts to Reduce Wildfire Risk |publisher=US Forest Service |access-date=19 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20120907045339/http://www.fs.fed.us/psw/publications/documents/psw_gtr208en/psw_gtr208en_505-512_haines.pdf |archive-date=7 September 2012 }}</ref> Wildfires are naturally occurring events that aid in promoting forest health. Global warming and climate changes are causing an increase in temperatures and more droughts nationwide which contributes to an increase in wildfire risk.<ref>{{cite web|url=http://msutoday.msu.edu/news/2013/extreme-wildfires-may-be-fueled-by-climate-change/|title=Extreme wildfires may be fueled by climate change|publisher=Michigan State University|date=1 August 2013|access-date=1 August 2013|url-status=live|archive-url=https://web.archive.org/web/20130803213631/http://msutoday.msu.edu/news/2013/extreme-wildfires-may-be-fueled-by-climate-change/|archive-date=3 August 2013}}</ref><ref>{{Cite AV media|url=https://www.youtube.com/watch?v=-mprIejWp00|title=White House explains the link between Climate Change and Wild Fires|date=5 August 2014|work=YouTube|author=Rajamanickam Antonimuthu|url-status=live|archive-url=https://web.archive.org/web/20140811074119/https://www.youtube.com/watch?v=-mprIejWp00|archive-date=11 August 2014}}</ref>
{{wide image|2009 California Wildfires at JPL - Pasadena, California.jpg|933px|The 2009 Station Fire burns in the foothills of the [[San Gabriel Mountains]] above the [[Jet Propulsion Laboratory]], near Pasadena, California}}

=== Airborne hazards ===
{{See also|Health effects of wood smoke}}
The most noticeable adverse effect of wildfires is the destruction of property. However, the release of hazardous chemicals from the burning of wildland fuels also significantly impacts health in humans.<ref>{{Cite web|url=https://www.purakamasks.com/how-did-forest-fires-affect-air-quality-in-california|title=How Have Forest Fires Affected Air Quality in California?|date=2019-02-05|website=www.purakamasks.com|language=en|access-date=2019-02-11}}</ref>

Wildfire smoke is composed primarily of carbon dioxide and water vapor. Other common smoke components present in lower concentrations are carbon monoxide, formaldehyde, acrolein, polyaromatic hydrocarbons, and benzene.<ref name="oehha.ca.gov">{{cite web|author=Office of Environmental Health Hazard Assessment|year=2008|title=Wildfire smoke: A guide for public health officials|access-date=9 July 2012|url=http://oehha.ca.gov/air/risk_assess/wildfirev8.pdf|url-status=live|archive-url=https://web.archive.org/web/20120516071549/http://www.oehha.ca.gov/air/risk_assess/wildfirev8.pdf|archive-date=16 May 2012}}</ref> Small particulates suspended in air which come in solid form or in liquid droplets are also present in smoke. 80 -90% of wildfire smoke, by mass, is within the fine particle size class of 2.5 micrometers in diameter or smaller.<ref>{{cite web|author=National Wildlife Coordination Group|year=2001|title=Smoke management guide for prescribed and wildland fire|location=Boise, ID|publisher=National Interagency Fire Center|url=http://www.fs.fed.us/pnw/pubs/ottmar-smoke-management-guide.pdf|url-status=live|archive-url=https://web.archive.org/web/20161011200515/http://www.fs.fed.us/pnw/pubs/ottmar-smoke-management-guide.pdf|archive-date=11 October 2016}}</ref>

Despite carbon dioxide's high concentration in smoke, it poses a low health risk due to its low toxicity. Rather, carbon monoxide and fine particulate matter, particularly 2.5&nbsp;µm in diameter and smaller, have been identified as the major health threats.<ref name="oehha.ca.gov" /> Other chemicals are considered to be significant hazards but are found in concentrations that are too low to cause detectable health effects.

The degree of wildfire smoke exposure to an individual is dependent on the length, severity, duration, and proximity of the fire. People are exposed directly to smoke via the respiratory tract through inhalation of air pollutants. Indirectly, communities are exposed to wildfire debris that can contaminate soil and water supplies.

The [[United States Environmental Protection Agency|U.S. Environmental Protection Agency]] (EPA) developed the [[air quality index]] (AQI), a public resource that provides national air quality standard concentrations for common air pollutants. The public can use this index as a tool to determine their exposure to hazardous air pollutants based on visibility range.<ref>{{cite web|author=U.S. Environmental Protection Agency|year=2009|title=Air quality index: A guide to air quality and health|access-date=9 July 2012|url=http://www.epa.gov/airnow/aqi_brochure_08-09.pdf|url-status=live|archive-url=https://web.archive.org/web/20120507130507/http://www.epa.gov/airnow/aqi_brochure_08-09.pdf|archive-date=7 May 2012}}</ref>

Fire ecologist Leda Kobziar found that wildfire smoke distributes microbial life on a global level.<ref>{{Cite web|url=https://wildfiretoday.com/2019/12/12/research-indicates-that-wildfire-smoke-may-distribute-microbial-life/|title=Research indicates that wildfire smoke may distribute microbial life|date=2019-12-12|website=Wildfire Today|language=en-US|access-date=2019-12-17}}</ref> She stated, "There are numerous allergens that we’ve found in the smoke. And so it may be that some people who are sensitive to smoke have that sensitivity, not only because of the particulate matter and the smoke but also because there are some biological organisms in it."<ref>{{Cite web|url=https://www.kqed.org/science/1951474/wildfire-smoke-once-considered-sterile-teems-with-life|title=Wildfire Smoke, Once Considered Sterile, Teems With Life|date=2019-12-10|website=KQED|language=en-us|access-date=2019-12-17}}</ref>

=== Water pollution ===
{{expand section|date=January 2021}}
Debris and chemical runoff into waterways after wildfires can make drinking water sources unsafe. Wildfires can damage water treatment and distribution infrastructure making drinking water unsafe. Drinking water inside buildings and in water distribution systems can be chemically contaminated. After the 2017 Tubbs Fire and 2018 Camp Fire in California hazardous waste levels of chemical contamination were found in multiple public drinking water systems impacted by wildfires.<ref>{{Cite journal|url=https://doi.org/10.1002/aws2.1183|doi=10.1002/aws2.1183|title=Wildfire caused widespread drinking water distribution network contamination|year=2020|last1=Proctor|first1=Caitlin R.|last2=Lee|first2=Juneseok|last3=Yu|first3=David|last4=Shah|first4=Amisha D.|last5=Whelton|first5=Andrew J.|journal=AWWA Water Science|volume=2|issue=4|s2cid=225641536}}</ref> Since 2018, wildfires that have damaged drinking water distribution systems in California and Oregon have caused contamination.<ref>{{Cite journal|url=https://doi.org/10.1007/s11069-021-04714-9|doi=10.1007/s11069-021-04714-9 | issn=0921-030X|title=Water safety attitudes, risk perception, experiences, and education for households impacted by the 2018 Camp Fire, California|year=2021|last1=Odimayomi|first1=Tolulope O.|last2=Proctor|first2=Caitlin R.|last3=Wang|first3=Qi Erica|last4=Sabbaghi|first4=Arman|last5=Peterson|first5=Kimberly S.|last6=Yu|first6=David J.|last7=Lee|first7=Juneseok|last8=Shah|first8=Amisha D.|last9=Ley|first9=Christian J.|last10=Noh|first10=Yoorae|last11=Smith|first11=Charlotte D.|last12=Webster|first12=Jackson P.|last13=Milinkevich|first13=Kristin|last14=Lodewyk|first14=Michael W.|last15=Jenks|first15=Julie A.|last16=Smith|first16=James F.|last17=Whelton|first17=Andrew J.|journal=Natural Hazards|volume=108|pages=947–975|s2cid=233478928}}</ref> Benzene is one of many chemicals that has been found in the drinking water systems after wildfires. Benzene can permeate certain plastic pipes and thus require long times to remove from the water distribution infrastructure. Using a U.S. Environmental Protection Agency model,<ref>{{Cite journal|url=https://doi.org/10.1061/(ASCE)EE.1943-7870.0001542|doi=10.1061/(ASCE)EE.1943-7870.0001542|title=Numerical Model for Decontamination of Organic Contaminants in Polyethylene Drinking Water Pipes in Premise Plumbing by Flushing|year=2019|last1=Haupert|first1=Levi M.|last2=Magnuson|first2=Matthew L.|journal=Journal of Environmental Engineering|volume=145|issue=7|pmid=32801447|pmc=7424390}}</ref> researchers estimated that more than 286 days of constant flushing of a single contaminated pipe, 24 hours per day, 7 days a week, were needed to reduce benzene below safe drinking water limits.<ref>{{Cite web|url=https://engineering.purdue.edu/PlumbingSafety/opinions/Final-HDPE-Service-Line-Decontamination-2019-03-18.pdf |title=Considerations for Decontaminating HDPE Service Lines by Flushing |website=engineering.purdue.edu |date=2019-03-18}}</ref> Temperature increases caused by fires, including wildfires, can cause plastic water pipes to generate toxic chemicals<ref>{{Cite journal|doi=10.1039/D0EW00836B|title=Drinking water contamination from the thermal degradation of plastics: Implications for wildfire and structure fire response|year=2021|last1=Isaacson|first1=Kristofer P.|last2=Proctor|first2=Caitlin R.|last3=Wang|first3=Q. Erica|last4=Edwards|first4=Ethan Y.|last5=Noh|first5=Yoorae|last6=Shah|first6=Amisha D.|last7=Whelton|first7=Andrew J.|journal=Environmental Science: Water Research & Technology|volume=7|issue=2|pages=274–284|s2cid=230567682|doi-access=free}}</ref> such as [[benzene]].<ref>{{Cite web |last= |first= |date=28 December 2020 |title=Plastic pipes are polluting drinking water systems after wildfires |url=https://arstechnica.com/science/2020/12/plastic-pipes-are-polluting-drinking-water-systems-after-wildfires/ |access-date=10 January 2021 |website=[[Ars Technica]]}}</ref>

Sediment inputs into streams and reservoirs alter the colour and murkiness of water increasing the chance of transporting particle-associated pollutants. Elevated sediment concentrations in drinking water make it more difficult to identify biological contaminants and increase microorganism development due to high quantities of nutrients.
[[File:Sediment off the Yucatan Peninsula.jpg|thumb|Sediment off the Yucatan Peninsula]]
Importantly, composite suspended sediment particles, instead of primary particles, might dominate the transit of little cohesive sediments through the stream system. microbial communities, organic and inorganic particles, and chemical components are all enclosed within the structure of those composite particles, which may have a negative impact on water quality. Burned aggregates have a lot of bigger sinking velocities than change state particles of equal diameter, which has been attributed to a rise in burned mixture density because of reduced organic content and pore house. Moreover, the impact of soil heating has been ascribed to the aggregation of clay particles into coarser composite particles, probably increasing the concentration of pollutants to composite particles relative to primary particles of equivalent size. Hyperbolic fine sediment storage and maybe delayed unharness of pollutants once fireplace from decaying aggregates are two potential implications of fireplace effects on soil particles.<ref>{{Cite journal|last1=Smith|first1=Hugh G.|last2=Sheridan|first2=Gary J.|last3=Lane|first3=Patrick N. J.|last4=Nyman|first4=Petter|last5=Haydon|first5=Shane|date=2011-01-05|title=Wildfire effects on water quality in forest catchments: A review with implications for water supply|url=https://www.sciencedirect.com/science/article/pii/S0022169410006748|journal=Journal of Hydrology|language=en|volume=396|issue=1|pages=170–192|doi=10.1016/j.jhydrol.2010.10.043|bibcode=2011JHyd..396..170S|issn=0022-1694}}</ref>

Recent studies that that conducted a global synthesis of fire effects on ecosystems found that forest fires have a significantly positive affect on water provision.<ref>{{Cite journal |last=Roces‐Díaz |first=Jose V |last2=Santín |first2=Cristina |last3=Martínez‐Vilalta |first3=Jordi |last4=Doerr |first4=Stefan H |date=April 2022 |title=A global synthesis of fire effects on ecosystem services of forests and woodlands |url=https://onlinelibrary.wiley.com/doi/10.1002/fee.2349 |journal=Frontiers in Ecology and the Environment |language=en |volume=20 |issue=3 |pages=170–178 |doi=10.1002/fee.2349 |issn=1540-9295}}</ref>

=== Post-fire risks ===
[[File:Prospect Hill bushfire.jpg|thumb|Charred shrubland in suburban [[Sydney]] ([[2019–20 Australian bushfire season|2019–20 Australian bushfires]]).]]
After a wildfire, hazards remain. Residents returning to their homes may be at risk from falling fire-weakened trees. Humans and pets may also be harmed by falling into [[ash pit]]s. The Intergovernmental Panel on Climate Change (IPCC) also reports that wildfires cause significant damage to electric systems, especially in dry regions.<ref>[https://report.ipcc.ch/ar6wg3/index.html IPCC Sixth Assessment Report 2022]</ref>

Other post-fire risks, can increase if other [[extreme weather]] follows. For example, wildfires make soil less able to absorb precipitation, so heavy rainfall can result in more severe [[flooding]] and damages like [[mud slide]]s.<ref>{{Cite book |last1=Movasat |first1=Mahta |last2=Tomac |first2=Ingrid |title=Geo-Congress 2020 |date=2020-02-21 |chapter=Post-Fire Mudflow Prevention by Biopolymer Treatment of Water Repellent Slopes |chapter-url=https://ascelibrary.org/doi/abs/10.1061/9780784482834.019 |language=en |pages=170–178 |doi=10.1061/9780784482834.019|isbn=9780784482834 |s2cid=213023120 }}</ref><ref>{{Cite journal |last=Palmer |first=Jane |date=2022-01-12 |title=The devastating mudslides that follow forest fires |url=https://www.nature.com/articles/d41586-022-00028-3 |journal=Nature |language=en |volume=601 |issue=7892 |pages=184–186 |doi=10.1038/d41586-022-00028-3|pmid=35022598 |bibcode=2022Natur.601..184P |s2cid=245907336 }}</ref>

=== At-risk groups ===

==== Firefighters ====
Firefighters are at the greatest risk for acute and chronic health effects resulting from wildfire smoke exposure. Due to firefighters' occupational duties, they are frequently exposed to [[Chemical hazard|hazardous chemicals]] at close proximity for longer periods of time. A case study on the exposure of wildfire smoke among wildland firefighters shows that firefighters are exposed to significant levels of carbon monoxide and respiratory irritants above [[Occupational Safety and Health Administration|OSHA]]-permissible exposure limits (PEL) and ACGIH threshold limit values (TLV). 5–10% are overexposed. The study obtained exposure concentrations for one wildland firefighter over a 10-hour shift spent holding down a fireline. The firefighter was exposed to a wide range of carbon monoxide and respiratory irritants (a combination of particulate matter 3.5&nbsp;µm and smaller, acrolein, and formaldehyde) levels. Carbon monoxide levels reached up to 160ppm and the TLV irritant index value reached a high of 10. In contrast, the OSHA PEL for carbon monoxide is 30ppm and for the TLV respiratory irritant index, the calculated threshold limit value is 1; any value above 1 exceeds exposure limits.<ref>{{cite journal|last2=Reinhardt|first2=T.E.|last3=Quiring|first3=S.J.|last4=Ottmar|first4=R.D.|year=2004|title=A screening-level assessment of the health risks of chronic smoke exposure for wildland firefighters|url=http://www.fs.fed.us/pnw/fera/publications/fulltext/boozeetal2004.pdf|journal=Journal of Occupational and Environmental Hygiene|volume=1|issue=5|pages=296–305|doi=10.1080/15459620490442500|pmid=15238338|last1=Booze|first1=T.F.|url-status=live|archive-url=https://web.archive.org/web/20170530185250/https://www.fs.fed.us/pnw/fera/publications/fulltext/boozeetal2004.pdf|archive-date=30 May 2017|citeseerx=10.1.1.541.5076|s2cid=24889908}}</ref>

Between 2001 and 2012, over 200 [[Occupational fatality|fatalities]] occurred among wildland firefighters. In addition to heat and chemical hazards, firefighters are also at risk for electrocution from power lines; injuries from equipment; [[Occupational injury|slips, trips, and falls]]; injuries from vehicle rollovers; [[Heat illness|heat-related illness]]; [[insect bites and stings]]; [[Occupational stress|stress]]; and [[rhabdomyolysis]].<ref>{{Cite journal|url=https://www.cdc.gov/niosh/docs/2013-158/|title=CDC – NIOSH Publications and Products – Wildland Fire Fighting: Hot Tips to Stay Safe and Healthy (2013–158)|website=www.cdc.gov|access-date=2016-11-22|url-status=live|archive-url=https://web.archive.org/web/20161122154309/http://www.cdc.gov/niosh/docs/2013-158/|archive-date=22 November 2016|doi=10.26616/NIOSHPUB2013158|year=2013|doi-access=free}}</ref>

==== Residents ====
[[File:North Complex smoke in San Francisco - Bay Bridge and Financial District.jpg|thumb|Smoke from the [[2020 California wildfires]] settles over [[San Francisco]]]]
Residents in communities surrounding wildfires are exposed to lower concentrations of chemicals, but they are at a greater risk for indirect exposure through water or soil contamination. Exposure to residents is greatly dependent on individual susceptibility. Vulnerable persons such as children (ages 0–4), the elderly (ages 65 and older), smokers, and pregnant women are at an increased risk due to their already compromised body systems, even when the exposures are present at low chemical concentrations and for relatively short exposure periods.<ref name="oehha.ca.gov" /> They are also at risk for future wildfires and may move away to areas they consider less risky.<ref>{{cite news |title=Living under a time bomb |url=https://www.washingtonpost.com/news/national/wp/2018/12/12/feature/living-under-a-time-bomb-california-communities-scramble-to-avoid-becoming-the-next-wildfire-tragedy/?noredirect=on&wpisrc=nl_rainbow&wpmm=1 |access-date=15 December 2018 |newspaper=[[The Washington Post]] |language=en}}</ref>

Wildfires affect large numbers of people in Western Canada and the United States. In California alone, more than 350,000 people live in towns and cities in "very high fire hazard severity zones".<ref name="rgj">{{cite news|page=1A |title=A real life gamble: California races to predict which town could be the next victim | author1=Ryan Sabalow |author2=Phillip Reese |author3=Dale Kasler |agency=The Sacramento Bee | publisher=Reno Gazette Journal |work=Destined to Burn}}</ref>

Direct risks to building residents in fire-prone areas can be moderated through design choices such as choosing fire-resistant vegetation, maintaining landscaping to avoid debris accumulation and to create firebreaks, and by selecting fire-retardant roofing materials. Potential compounding issues with poor air quality and heat during warmer months may be addressed with MERV 11 or higher outdoor air filtration in building ventilation systems, mechanical cooling, and a provision of a refuge area with additional air cleaning and cooling, if needed.<ref>{{cite web |title=Design Discussion Primer - Wildfires |url=https://www.bchousing.org/publications/MBAR-Wildfires.pdf |publisher=BC Housing |access-date=16 July 2021}}</ref>

== Health effects ==
{{See also|Atmospheric particulate matter|Health effects of wood smoke|Household air pollution#Health impacts}}

[[File:Diaphragmatic breathing.gif|thumb|Animation of diaphragmatic breathing with the diaphragm shown in green]]

Wildfire smoke contains particulate matter that may have adverse effects upon the human respiratory system. Evidence of the health effects of wildfire smoke should be relayed to the public so that exposure may be limited. Evidence of health effects can also be used to influence policy to promote positive health outcomes.<ref name=":11">{{Cite journal|last1=Liu|first1=Jia Coco|last2=Wilson|first2=Ander|last3=Mickley|first3=Loretta J.|last4=Dominici|first4=Francesca|last5=Ebisu|first5=Keita|last6=Wang|first6=Yun|last7=Sulprizio|first7=Melissa P.|last8=Peng|first8=Roger D.|last9=Yue|first9=Xu|date=January 2017|title=Wildfire-specific Fine Particulate Matter and Risk of Hospital Admissions in Urban and Rural Counties|journal=Epidemiology|language=en|volume=28|issue=1|pages=77–85|doi=10.1097/ede.0000000000000556|issn=1044-3983|pmc=5130603|pmid=27648592}}</ref>

Inhalation of smoke from a wildfire can be a health hazard.<ref>{{Cite web|url=https://www.cleanairresources.com/resources/side-effects-of-wildfire-smoke-inhalation|title=Side Effects of Wildfire Smoke Inhalation|date=2019-03-11|website=www.cleanairresources.com|language=en|access-date=2019-04-03}}</ref> Wildfire smoke is composed of combustion products i.e. [[carbon dioxide]], [[carbon monoxide]], [[water vapor]], [[particulate matter]], organic chemicals, [[nitrogen oxide]]s and other compounds. The principal health concern is the inhalation of particulate matter and carbon monoxide.<ref>{{cite web |url=http://www.epa.gov/ttnamti1/files/ambient/smoke/wildgd.pdf |title=1 Wildfire Smoke A Guide for Public Health Officials |publisher=US Environmental Protection Agency |access-date=19 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20130509110731/http://www.epa.gov/ttnamti1/files/ambient/smoke/wildgd.pdf |archive-date=9 May 2013 }}</ref>

Particulate matter (PM) is a type of air pollution made up of particles of dust and liquid droplets. They are characterized into three categories based on the diameter of the particle: coarse PM, fine PM, and ultrafine PM. Coarse particles are between 2.5 micrometers and 10 micrometers, fine particles measure 0.1 to 2.5 micrometers, and ultrafine particle are less than 0.1 micrometer. &nbsp;Each size can enter the body through inhalation, but the PM impact on the body varies by size. Coarse particles are filtered by the upper airways and these particles can accumulate and cause pulmonary inflammation. This can result in eye and sinus irritation as well as sore throat and coughing.<ref name=":10" /><ref name=":12">{{Cite journal|last1=Wu|first1=Jin-Zhun|last2=Ge|first2=Dan-Dan|last3=Zhou|first3=Lin-Fu|last4=Hou|first4=Ling-Yun|last5=Zhou|first5=Ying|last6=Li|first6=Qi-Yuan|date=June 2018|title=Effects of particulate matter on allergic respiratory diseases|journal=Chronic Diseases and Translational Medicine|volume=4|issue=2|pages=95–102|doi=10.1016/j.cdtm.2018.04.001|issn=2095-882X|pmc=6034084|pmid=29988900}}</ref> Coarse PM is often composed of materials that are heavier and more toxic that lead to short-term effects with stronger impact.<ref name=":12" />

Smaller particulate moves further into the respiratory system creating issues deep into the lungs and the bloodstream.<ref name=":10" /><ref name=":12" /> In asthma patients, PM<sub>2.5</sub> causes inflammation but also increases oxidative stress in the epithelial cells. These particulates also cause apoptosis and autophagy in lung epithelial cells. Both processes cause the cells to be damaged and impacts the cell function. This damage impacts those with respiratory conditions such as asthma where the lung tissues and function are already compromised.<ref name=":12" /> The third PM type is ultra-fine PM (UFP). UFP can enter the bloodstream like PM<sub>2.5</sub> however studies show that it works into the blood much quicker. The inflammation and epithelial damage done by UFP has also shown to be much more severe.<ref name=":12" /> PM<sub>2.5</sub> is of the largest concern in regards to wildfire.<ref name=":11" /> This is particularly hazardous to the very young, elderly and those with chronic conditions such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis and cardiovascular conditions. The illnesses most commonly with exposure to the fine particles from wildfire smoke are bronchitis, exacerbation of asthma or COPD, and pneumonia. Symptoms of these complications include wheezing and shortness of breath and cardiovascular symptoms include chest pain, rapid heart rate and fatigue.<ref name=":10">{{cite journal |doi=10.1016/j.nurpra.2011.07.001 |title=Wildfire Smoke Exposure: A Guide for the Nurse Practitioner |date=2012 |last1=Forsberg |first1=Nicole T. |last2=Longo |first2=Bernadette M. |last3=Baxter |first3=Kimberly |last4=Boutté |first4=Marie |journal=[[The Journal for Nurse Practitioners]] |volume=8 |issue=2 |pages=98–106}}</ref>

=== Asthma exacerbation ===
Smoke from wildfires can cause health problems, especially for children and those who already have respiratory problems.<ref name=":13">{{Cite journal|last1=Hutchinson|first1=Justine A.|last2=Vargo|first2=Jason|last3=Milet|first3=Meredith|last4=French|first4=Nancy H. F.|last5=Billmire|first5=Michael|last6=Johnson|first6=Jeffrey|last7=Hoshiko|first7=Sumi|date=2018-07-10|title=The San Diego 2007 wildfires and Medi-Cal emergency department presentations, inpatient hospitalizations, and outpatient visits: An observational study of smoke exposure periods and a bidirectional case-crossover analysis|journal=PLOS Medicine|volume=15|issue=7|pages=e1002601|doi=10.1371/journal.pmed.1002601|issn=1549-1676|pmc=6038982|pmid=29990362}}</ref> Several epidemiological studies have demonstrated a close association between [[air pollution]] and respiratory allergic diseases such as bronchial [[asthma]].<ref name=":11" />

An observational study of smoke exposure related to the 2007 San Diego wildfires revealed an increase both in healthcare utilization and respiratory diagnoses, especially [[asthma]] among the group sampled.<ref name=":13" /> Projected climate scenarios of wildfire occurrences predict significant increases in respiratory conditions among young children.<ref name=":13" /> [[Particulates|Particulate Matter (PM)]] triggers a series of biological processes including inflammatory immune response, [[oxidative stress]], which are associated with harmful changes in allergic respiratory diseases.<ref>{{Cite journal|last1=Wu|first1=Jin-Zhun|last2=Ge|first2=Dan-Dan|last3=Zhou|first3=Lin-Fu|last4=Hou|first4=Ling-Yun|last5=Zhou|first5=Ying|last6=Li|first6=Qi-Yuan|date=2018-06-08|title=Effects of particulate matter on allergic respiratory diseases|journal=Chronic Diseases and Translational Medicine|volume=4|issue=2|pages=95–102|doi=10.1016/j.cdtm.2018.04.001|issn=2095-882X|pmc=6034084|pmid=29988900}}</ref>

Although some studies demonstrated no significant acute changes in lung function among people with [[asthma]] related to PM from wildfires, a possible explanation for these counterintuitive findings is the increased use of [[Asthma|quick-relief medications]], such as inhalers, in response to elevated levels of smoke among those already diagnosed with [[asthma]].<ref name=":14">{{Cite journal|last1=Reid|first1=Colleen E.|last2=Brauer|first2=Michael|last3=Johnston|first3=Fay H.|last4=Jerrett|first4=Michael|last5=Balmes|first5=John R.|last6=Elliott|first6=Catherine T.|date=2016-04-15|title=Critical Review of Health Impacts of Wildfire Smoke Exposure|journal=Environmental Health Perspectives|language=en|volume=124|issue=9|pages=1334–1343|doi=10.1289/ehp.1409277|issn=0091-6765|pmc=5010409|pmid=27082891}}</ref> In investigating the association of medication use for obstructive lung disease and wildfire exposure, researchers found increases both in the usage of inhalers and initiation of long-term control as in oral steroids.<ref name=":14" /> More specifically, some people with [[asthma]] reported higher use of [[Asthma|quick-relief medications]] (inhalers).<ref name=":14" /> After two major wildfires in California, researchers found an increase in physician prescriptions for [[Asthma|quick-relief medications]] in the years following the wildfires than compared to the year before each occurrence.<ref name=":14" />

There is consistent evidence between wildfire smoke and the exacerbation of asthma.<ref name=":14" />

==== Fatal exposure ====
Asthma is one of the most common chronic disease among children in the United States, affecting an estimated 6.2 million children.<ref>{{Cite web |date=19 October 2018 |title=American Lung Association and Asthma Fact sheet |url=http://www.lung.org/lung-health-and-diseases/lung-disease-lookup/asthma/learn-about-asthma/asthma-children-facts-sheet.html |url-status=live |archive-url=https://web.archive.org/web/20151116182804/http://www.lung.org/lung-health-and-diseases/lung-disease-lookup/asthma/learn-about-asthma/asthma-children-facts-sheet.html |archive-date=16 November 2015 |website=American Lung Association}}</ref> Research on asthma risk focuses specifically on the risk of air pollution during the gestational period. Several pathophysiology processes are involved are in this. Considerable airway development occurs during the 2nd and 3rd trimester and continues until 3 years of age.<ref>{{Cite journal |last1=Nishimura |first1=Katherine K. |last2=Galanter |first2=Joshua M. |last3=Roth |first3=Lindsey A. |last4=Oh |first4=Sam S. |last5=Thakur |first5=Neeta |last6=Nguyen |first6=Elizabeth A. |last7=Thyne |first7=Shannon |last8=Farber |first8=Harold J. |last9=Serebrisky |first9=Denise |date=August 2013 |title=Early-Life Air Pollution and Asthma Risk in Minority Children. The GALA II and SAGE II Studies |journal=American Journal of Respiratory and Critical Care Medicine |language=en |volume=188 |issue=3 |pages=309–318 |doi=10.1164/rccm.201302-0264oc |issn=1073-449X |pmc=3778732 |pmid=23750510}}</ref> It is hypothesized that exposure to these toxins during this period could have consequential effects, as the epithelium of the lungs during this time could have increased permeability to toxins. Exposure to air pollution during parental and pre-natal stage could induce epigenetic changes which are responsible for the development of asthma.<ref>{{Cite journal |last1=Hsu |first1=Hsiao-Hsien Leon |last2=Chiu |first2=Yueh-Hsiu Mathilda |last3=Coull |first3=Brent A. |last4=Kloog |first4=Itai |last5=Schwartz |first5=Joel |last6=Lee |first6=Alison |last7=Wright |first7=Robert O. |last8=Wright |first8=Rosalind J. |date=2015-11-01 |title=Prenatal Particulate Air Pollution and Asthma Onset in Urban Children. Identifying Sensitive Windows and Sex Differences |journal=American Journal of Respiratory and Critical Care Medicine |volume=192 |issue=9 |pages=1052–1059 |doi=10.1164/rccm.201504-0658OC |issn=1535-4970 |pmc=4642201 |pmid=26176842}}</ref> Studies have found significant association between PM<sub>2.5</sub>, NO<sub>2</sub> and development of asthma during childhood despite heterogeneity among studies.<ref>{{Cite journal |last1=Hehua |first1=Zhang |last2=Qing |first2=Chang |last3=Shanyan |first3=Gao |last4=Qijun |first4=Wu |last5=Yuhong |first5=Zhao |date=November 2017 |title=The impact of prenatal exposure to air pollution on childhood wheezing and asthma: A systematic review |journal=Environmental Research |volume=159 |pages=519–530 |bibcode=2017ER....159..519H |doi=10.1016/j.envres.2017.08.038 |issn=0013-9351 |pmid=28888196 |s2cid=22300866}}</ref> Furthermore, maternal exposure to chronic stressors is most likely present in distressed communities, and as this can be correlated with childhood asthma, it may further explain links between early childhood exposure to air pollution, neighborhood poverty, and childhood risk. As well, living in distressed neighborhoods is linked to pollutant source location and exposure and also to greater chronic individual stress, which alters the allostatic load of the maternal immune system. In turn, this leads to adverse outcomes in children, including increased susceptibility to air pollution.<ref>{{Cite journal |last1=Morello-Frosch |first1=Rachel |last2=Shenassa |first2=Edmond D. |date=August 2006 |title=The Environmental "Riskscape" and Social Inequality: Implicationsfor Explaining Maternal and Child Health Disparities |journal=Environmental Health Perspectives |language=en |volume=114 |issue=8 |pages=1150–1153 |doi=10.1289/ehp.8930 |issn=0091-6765 |pmc=1551987 |pmid=16882517}}</ref>

=== Carbon monoxide danger ===
{{Main|Carbon monoxide poisoning}}

Carbon monoxide (CO) is a colorless, odorless gas that can be found at the highest concentration at close proximity to a smoldering fire. For this reason, carbon monoxide inhalation is a serious threat to the health of wildfire firefighters. CO in smoke can be inhaled into the lungs where it is absorbed into the bloodstream and reduces oxygen delivery to the body's vital organs. At high concentrations, it can cause headaches, weakness, dizziness, confusion, nausea, disorientation, visual impairment, coma, and even death. However, even at lower concentrations, such as those found at wildfires, individuals with cardiovascular disease may experience chest pain and cardiac arrhythmia.<ref name="oehha.ca.gov" /> A recent study tracking the number and cause of wildfire firefighter deaths from 1990–2006 found that 21.9% of the deaths occurred from heart attacks.<ref>{{cite web|author=National Wildfire Coordinating Group|date=June 2007|title=Wildland firefighter fatalities in the United States 1990–2006|publisher=NWCG Safety and Health Working Team|url=http://www.nwcg.gov/pms/pubs/pms841/pms841_all-72dpi.pdf|url-status=live|archive-url=https://web.archive.org/web/20120315081248/http://www.nwcg.gov/pms/pubs/pms841/pms841_all-72dpi.pdf|archive-date=15 March 2012}}</ref>

Another important and somewhat less obvious health effect of wildfires is psychiatric diseases and disorders. Both adults and children from countries ranging from the United States and Canada to Greece and Australia who were directly and indirectly affected by wildfires were found by researchers to demonstrate several different mental conditions linked to their experience with the wildfires. These include [[Post-traumatic stress disorder among athletes|post-traumatic stress disorder]] (PTSD), [[Depression (mood)|depression]], anxiety, and [[phobia]]s.<ref>{{cite journal |pmid=21957753 |date=2011 |last1=Papanikolaou |first1=V |last2=Adamis |first2=D |last3=Mellon |first3=RC |last4=Prodromitis |first4=G |title=Psychological distress following wildfires disaster in a rural part of Greece: A case-control population-based study |volume=13 |issue=1 |pages=11–26 |journal=International Journal of Emergency Mental Health}}</ref><ref>{{cite journal |doi=10.1002/jts.20411 |title=Locus of control and psychopathology in relation to levels of trauma and loss: Self-reports of Peloponnesian wildfire survivors |date=2009 |last1=Mellon |first1=Robert C. |last2=Papanikolau |first2=Vasiliki |last3=Prodromitis |first3=Gerasimos |journal=Journal of Traumatic Stress |volume=22 |issue=3 |pages=189–196 |pmid=19452533}}</ref><ref>{{cite journal |doi=10.1176/appi.ps.58.4.509 |title=Psychiatric Disorders Among Adults Seeking Emergency Disaster Assistance After a Wildland-Urban Interface Fire |date=2007 |last1=Marshall |first1=G. N. |last2=Schell |first2=T. L. |last3=Elliott |first3=M. N. |last4=Rayburn |first4=N. R. |last5=Jaycox |first5=L. H. |journal=Psychiatric Services |volume=58 |issue=4 |pages=509–514 |pmid=17412853}}</ref><ref>{{cite journal |pmid=15830823 |date=2005 |last1=McDermott |first1=BM |last2=Lee |first2=EM |last3=Judd |first3=M |last4=Gibbon |first4=P |title=Posttraumatic stress disorder and general psychopathology in children and adolescents following a wildfire disaster |volume=50 |issue=3 |pages=137–143 |journal=Canadian Journal of Psychiatry|doi=10.1177/070674370505000302 |s2cid=38364512 |url=http://espace.library.uq.edu.au/view/UQ:78468/UQ78468_OA.pdf }}<!--http://espace.library.uq.edu.au/view/UQ:78468/UQ78468_OA.pdf--></ref><ref>{{cite journal |pmid=11961911 |date=2002 |last1=Jones |first1=RT |last2=Ribbe |first2=DP |last3=Cunningham |first3=PB |last4=Weddle |first4=JD |last5=Langley |first5=AK |title=Psychological impact of fire disaster on children and their parents |volume=26 |issue=2 |pages=163–186 |journal=Behavior Modification |doi=10.1177/0145445502026002003|s2cid=629959 }}</ref>

=== Epidemiology ===
The western US has seen an increase in both the frequency and intensity of wildfires over the last several decades. This increase has been attributed to the arid climate of the western US and the effects of global warming. An estimated 46 million people were exposed to wildfire smoke from 2004 to 2009 in the Western United States. Evidence has demonstrated that wildfire smoke can increase levels of particulate matter in the atmosphere.<ref name=":11" />

The EPA has defined acceptable concentrations of particulate matter in the air, through the National Ambient Air Quality Standards and monitoring of ambient air quality has been mandated.<ref name=":15">{{cite web|url=http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.html|title=Particulate Matter (PM) Standards|date=24 April 2016|publisher=EPA|url-status=live|archive-url=https://web.archive.org/web/20120815125540/http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.html|archive-date=15 August 2012}}</ref> Due to these monitoring programs and the incidence of several large wildfires near populated areas, epidemiological studies have been conducted and demonstrate an association between human health effects and an increase in fine particulate matter due to wildfire smoke.

The EPA has defined acceptable concentrations of particulate matter in the air. The National Ambient Air Quality Standards are part of the Clean Air Act and provide mandated guidelines for pollutant levels and the monitoring of ambient air quality.<ref name=":15" /> In addition to these monitoring programs, the increased incidence of wildfires near populated areas has precipitated several epidemiological studies. Such studies have demonstrated an association between negative human health effects and an increase in fine particulate matter due to wildfire smoke. The size of the particulate matter is significant as smaller particulate matter (fine) is easily inhaled into the human respiratory tract. Often, small particulate matter can be inhaled into deep lung tissue causing respiratory distress, illness, or disease.<ref name=":11" />

An increase in PM smoke emitted from the Hayman fire in Colorado in June 2002, was associated with an increase in respiratory symptoms in patients with COPD.<ref>{{cite journal |doi=10.1016/j.jaci.2004.11.030 |title=Wildfire smoke and respiratory symptoms in patients with chronic obstructive pulmonary disease |date=2005 |last1=Sutherland |first1=E. Rand |last2=Make |first2=Barry J. |last3=Vedal |first3=Sverre |last4=Zhang |first4=Lening |last5=Dutton |first5=Steven J. |last6=Murphy |first6=James R. |last7=Silkoff |first7=Philip E. |journal=Journal of Allergy and Clinical Immunology |volume=115 |issue=2 |pages=420–422 |pmid=15696107}}</ref> Looking at the wildfires in Southern California in October 2003 in a similar manner, investigators have shown an increase in hospital admissions due to asthma symptoms while being exposed to peak concentrations of PM in smoke.<ref>{{cite journal |doi=10.1136/oem.2008.041376 |title=The relationship of respiratory and cardiovascular hospital admissions to the southern California wildfires of 2003 |date=2009 |last1=Delfino |first1=R J |last2=Brummel |first2=S |last3=Wu |first3=J |last4=Stern |first4=H |last5=Ostro |first5=B |last6=Lipsett |first6=M |last7=Winer |first7=A |last8=Street |first8=D H |last9=Zhang |first9=L |journal=Occupational and Environmental Medicine |volume=66 |issue=3 |pages=189–197 |pmid=19017694 |last10=Tjoa |first10=T |last11=Gillen |first11=D L|pmc=4176821 }}</ref> Another epidemiological study found a 7.2% (95% confidence interval: 0.25%, 15%) increase in risk of respiratory related hospital admissions during smoke wave days with high wildfire-specific particulate matter 2.5 compared to matched non-smoke-wave days.<ref name=":11" />

Children participating in the Children's Health Study were also found to have an increase in eye and respiratory symptoms, medication use and physician visits.<ref>{{cite journal |doi=10.1164/rccm.200604-519OC |title=Health Effects of the 2003 Southern California Wildfires on Children |date=2006 |last1=Kunzli |first1=N. |last2=Avol |first2=E. |last3=Wu |first3=J. |last4=Gauderman |first4=W. J. |last5=Rappaport |first5=E. |last6=Millstein |first6=J. |last7=Bennion |first7=J. |last8=McConnell |first8=R. |last9=Gilliland |first9=F. D. |journal=American Journal of Respiratory and Critical Care Medicine |volume=174 |issue=11 |pages=1221–1228 |pmid=16946126 |pmc=2648104 |last10=Berhane |first10=Kiros |last11=Lurmann |first11=Fred |last12=Winer |first12=Arthur |last13=Peters |first13=John M.}}</ref> Recently, it was demonstrated that mothers who were pregnant during the fires gave birth to babies with a slightly reduced average birth weight compared to those who were not exposed to wildfire during birth. Suggesting that pregnant women may also be at greater risk to adverse effects from wildfire.<ref>{{cite journal |doi=10.1289/ehp.1104515 |title=Birth Weight Following Pregnancy During the 2003 Southern California Wildfires |date=2012 |last1=Holstius |first1=David M. |last2=Reid |first2=Colleen E. |last3=Jesdale |first3=Bill M. |last4=Morello-Frosch |first4=Rachel |journal=Environmental Health Perspectives |volume=120 |issue=9 |pages=1340–1345 |pmid=22645279 |pmc=3440113}}</ref> Worldwide it is estimated that 339,000 people die due to the effects of wildfire smoke each year.<ref>{{cite journal|last=Johnston|first=Fay H.|display-authors=etal|title=Estimated global mortality attributable to smoke from landscape fires|journal=Environmental Health Perspectives|date=May 2012|url=http://www.fire.uni-freiburg.de/vfe/Landscape-Fire-Smoke-Global-Mortality-Johnston-2012.pdf|volume=120|issue=5|pages=695–701|doi=10.1289/ehp.1104422|pmc=3346787|pmid=22456494|url-status=dead|archive-url=https://web.archive.org/web/20160522061115/http://www.fire.uni-freiburg.de/vfe/Landscape-Fire-Smoke-Global-Mortality-Johnston-2012.pdf|archive-date=22 May 2016|access-date=9 December 2018}}</ref>

While the size of particulate matter is an important consideration for health effects, the chemical composition of particulate matter (PM<sub>2.5</sub>) from wildfire smoke should also be considered. Antecedent studies have demonstrated that the chemical composition of PM<sub>2.5</sub> from wildfire smoke can yield different estimates of human health outcomes as compared to other sources of smoke.<ref name=":11" /> health outcomes for people exposed to wildfire smoke may differ from those exposed to smoke from alternative sources such as solid fuels.

== History ==
{{Further|Fossil record of fire}}
[[File:Deerfire high res.jpg|thumb|left|''[[Elk Bath]]'', an award winning photograph of elk avoiding a wildfire in [[Montana]]]]

The first evidence of wildfires is fossils of the giant fungi [[Prototaxites]] preserved as [[charcoal]], discovered in [[South Wales]] and [[Poland]], dating to the [[Silurian]] period (about {{ma|430}}).<ref>[https://www.bbc.com/news/science-environment-61929966 Earliest evidence of wildfire found in Wales – BBC News]</ref> Smoldering surface fires started to occur sometime before the Early [[Devonian]] period {{ma|405}}. Low atmospheric oxygen during the Middle and Late Devonian was accompanied by a decrease in charcoal abundance.<ref name="Glasspool">{{cite journal|last1=Glasspool|first1=IJ|last2=Edwards|first2=D|last3=Axe|first3=L|year=2004|title=Charcoal in the Silurian as evidence for the earliest wildfire|journal=Geology|volume=32|issue=5|pages=381–383|bibcode=2004Geo....32..381G|doi=10.1130/G20363.1}}</ref><ref>{{cite journal|last1=Edwards|first1=D.|last2=Axe|first2=L.|date=April 2004|title=Anatomical Evidence in the Detection of the Earliest Wildfires|journal=PALAIOS|volume=19|issue=2|pages=113–128|bibcode=2004Palai..19..113E|doi=10.1669/0883-1351(2004)019<0113:AEITDO>2.0.CO;2|s2cid=129438858 |issn=0883-1351}}</ref> Additional charcoal evidence suggests that fires continued through the [[Carboniferous]] period. Later, the overall increase of atmospheric oxygen from 13% in the Late Devonian to 30–31% by the [[Late Permian]] was accompanied by a more widespread distribution of wildfires.<ref name="Scott2006">{{Cite journal|last1=Scott|first1=C.|last2=Glasspool|first2=J.|date=Jul 2006|title=The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=103|issue=29|pages=10861–10865|bibcode=2006PNAS..10310861S|doi=10.1073/pnas.0604090103|issn=0027-8424|pmc=1544139|pmid=16832054|doi-access=free}}</ref> Later, a decrease in wildfire-related charcoal deposits from the late Permian to the [[Triassic]] periods is explained by a decrease in oxygen levels.<ref name="Pausas 594">Pausas and Keeley, 594</ref>

Wildfires during the Paleozoic and Mesozoic periods followed patterns similar to fires that occur in modern times. Surface fires driven by dry seasons{{clarify|does this mean annual dry seasons or erratic droughts?|date=October 2015}} are evident in Devonian and Carboniferous [[progymnosperm]] forests. [[Lepidodendron]] forests dating to the Carboniferous period have charred peaks, evidence of crown fires. In Jurassic [[gymnosperm]] forests, there is evidence of high frequency, light surface fires.<ref name="Pausas 594" /> The increase of fire activity in the late [[Tertiary]]<ref name="cenozoic-division">Historically, the [[Cenozoic]] has been divided up into the [[Quaternary]] and [[Tertiary]] sub-eras, as well as the [[Neogene]] and [[Paleogene]] periods. The [http://www.stratigraphy.org/upload/ISChart2009.pdf 2009 version of the ICS time chart] {{webarchive|url=https://web.archive.org/web/20091229003212/http://www.stratigraphy.org/upload/ISChart2009.pdf|date=29 December 2009}} recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status.</ref> is possibly due to the increase of [[C4 carbon fixation|C<sub>4</sub>]]-type grasses. As these grasses shifted to more [[mesic habitat]]s, their high flammability increased fire frequency, promoting grasslands over woodlands.<ref>Pausas and Keeley, 595</ref> However, fire-prone habitats may have contributed to the prominence of trees such as those of the genera ''[[Eucalyptus]]'', ''Pinus'' and ''[[Sequoia (genus)|Sequoia]]'', which have thick bark to withstand fires and employ [[serotiny#Fire-mediated serotiny|pyriscence]].<ref>Pausas and Keeley, 596</ref><ref>[http://www.shannontech.com/ParkVision/Redwood/Redwood2.html "Redwood Trees"] {{webarchive|url=https://web.archive.org/web/20150901062508/http://www.shannontech.com/ParkVision/Redwood/Redwood2.html|date=1 September 2015}}.</ref>

=== Human involvement ===
{{See also|Control of fire by early humans|Deforestation#Historical causes|Environmental history|History of firefighting|Native American use of fire}}
[[File:Burning mountains Thailand.JPG|thumb|upright=1.2|Aerial view of deliberate wildfires on the [[Khun Tan Range]], [[Thailand]]. These fires are lit by local farmers every year to promote the growth of a certain mushroom]]
The human use of fire for agricultural and hunting purposes during the [[Paleolithic]] and [[Mesolithic]] ages altered the preexisting landscapes and fire regimes. Woodlands were gradually replaced by smaller vegetation that facilitated travel, hunting, seed-gathering and planting.<ref>Pausas and Keeley, 597</ref> In recorded human history, minor allusions to wildfires were mentioned in the [[Bible]] and by classical writers such as [[Homer]]. However, while ancient Hebrew, Greek, and Roman writers were aware of fires, they were not very interested in the uncultivated lands where wildfires occurred.<ref name="RackhamFire">{{cite journal|last=Rackham|first=Oliver|author-link=Oliver Rackham|date=November–December 2003|title=Fire in the European Mediterranean: History|url=http://ag.arizona.edu/OALS/ALN/aln54/rackham.html#hist|url-status=live|journal=AridLands Newsletter|volume=54|archive-url=https://web.archive.org/web/20081011110940/http://ag.arizona.edu/OALS/ALN/aln54/rackham.html#hist|archive-date=11 October 2008|access-date=17 July 2009}}</ref><ref name="RackhamHist">Rackham, 229–230</ref> Wildfires were used in battles throughout human history as [[early thermal weapons]]. From the [[Middle ages]], accounts were written of [[occupational burning]] as well as customs and laws that governed the use of fire. In Germany, regular burning was documented in 1290 in the [[Odenwald]] and in 1344 in the [[Black Forest]].<ref name="Goldammer">{{cite conference|last=Goldammer|first=Johann G.|date=5–9 May 1998|title=History of Fire in Land-Use Systems of the Baltic Region: Implications on the Use of Prescribed Fire in Forestry, Nature Conservation and Landscape Management|url=http://www.fire.uni-freiburg.de/programmes/natcon/natcon_1.htm|publisher=Global Fire Monitoring Center (GFMC)|archive-url=https://web.archive.org/web/20090816155656/http://www.fire.uni-freiburg.de/programmes/natcon/natcon_1.htm|archive-date=16 August 2009|access-date=9 December 2018|book-title=First Baltic Conference on Forest Fires|place=Radom-Katowice, Poland|url-status=dead}}</ref> In the 14th century [[Sardinia]], firebreaks were used for wildfire protection. In Spain during the 1550s, [[sheep husbandry]] was discouraged in certain provinces by [[Philip II of Spain|Philip II]] due to the harmful effects of fires used in [[transhumance]].<ref name="RackhamFire" /><ref name="RackhamHist" /> As early as the 17th century, Native Americans were observed [[Native American use of fire|using fire]] for many purposes including cultivation, [[Smoke signal|signaling]], and warfare. Scottish botanist [[David Douglas (botanist)|David Douglas]] noted the native use of fire for tobacco cultivation, to encourage deer into smaller areas for hunting purposes, and to improve foraging for honey and grasshoppers. Charcoal found in sedimentary deposits off the Pacific coast of Central America suggests that more burning occurred in the 50 years before the [[Spanish colonization of the Americas]] than after the colonization.<ref>{{cite journal|date=Summer 2000|title=Wildland fire – An American legacy&#124;|url=http://www.fs.fed.us/fire/fmt/fmt_pdfs/fmn60-3.pdf|url-status=live|journal=Fire Management Today|volume=60|issue=3|pages=4, 5, 9, 11|archive-url=https://web.archive.org/web/20100401085836/http://www.fs.fed.us/fire/fmt/fmt_pdfs/fmn60-3.pdf|archive-date=1 April 2010|access-date=31 July 2009}}</ref> In the post-World War II [[Baltic region]], socio-economic changes led more stringent air quality standards and bans on fires that eliminated traditional burning practices.<ref name="Goldammer" /> In the mid-19th century, explorers from {{HMS|Beagle}} observed [[Australian Aborigines]] using fire for ground clearing, hunting, and regeneration of plant food in a method later named [[fire-stick farming]].<ref>''Fire. The Australian Experience'', 7.</ref> Such careful use of fire has been employed for centuries in the lands protected by [[Kakadu National Park]] to encourage biodiversity.<ref>Karki, 27.</ref>

Wildfires typically occurred during periods of increased temperature and [[drought]]. An increase in fire-related [[debris flow]] in [[alluvial fan]]s of northeastern [[Yellowstone National Park]] was linked to the period between AD 1050 and 1200, coinciding with the [[Medieval Warm Period]].<ref>{{cite journal|last1=Meyer|first1=G.A.|last2=Wells|first2=S.G.|last3=Jull|first3=A.J.T.|date=1995|title=Fire and alluvial chronology in Yellowstone National Park: Climatic and intrinsic controls on Holocene geomorphic processes|journal=GSA Bulletin|volume=107|issue=10|pages=1211–1230|bibcode=1995GSAB..107.1211M|doi=10.1130/0016-7606(1995)107<1211:FAACIY>2.3.CO;2}}</ref> However, human influence caused an increase in fire frequency. [[Dendrochronological]] fire scar data and charcoal layer data in [[Finland]] suggests that, while many fires occurred during severe drought conditions, an increase in the number of fires during 850 BC and 1660 AD can be attributed to human influence.<ref>Pitkänen, ''et al.'', 15–16 and 27–30</ref> Charcoal evidence from the Americas suggested a general decrease in wildfires between 1 AD and 1750 compared to previous years. However, a period of increased fire frequency between 1750 and 1870 was suggested by charcoal data from North America and Asia, attributed to human population growth and influences such as land clearing practices. This period was followed by an overall decrease in burning in the 20th century, linked to the expansion of agriculture, increased livestock grazing, and fire prevention efforts.<ref>{{cite journal|author=J. R. Marlon|author2=P. J. Bartlein|author3=C. Carcaillet|author4=D. G. Gavin|author5=S. P. Harrison|author6=P. E. Higuera|author7=F. Joos|author8=M. J. Power|author9=I. C. Prentice|date=2008|title=Climate and human influences on global biomass burning over the past two millennia|journal=Nature Geoscience|volume=1|issue=10|pages=697–702|bibcode=2008NatGe...1..697M|doi=10.1038/ngeo313}} [http://pmr.uoregon.edu/science-and-innovation/uo-research-news/research-news-2008/september-2008/climate-change-human-activity-and-wildfires-1/ University of Oregon Summary, accessed 2 February 2010]{{webarchive|url=https://web.archive.org/web/20080927051047/http://pmr.uoregon.edu/science-and-innovation/uo-research-news/research-news-2008/september-2008/climate-change-human-activity-and-wildfires-1/|date=27 September 2008}}</ref> A meta-analysis found that 17 times more land burned annually in California before 1800 compared to recent decades (1,800,000 hectares/year compared to 102,000 hectares/year).<ref>{{cite journal|last1=Stephens|first1=Scott L.|last2=Martin|first2=Robert E.|last3=Clinton|first3=Nicholas E.|date=2007|title=Prehistoric fire area and emissions from California's forests, woodlands, shrublands, and grasslands|journal=Forest Ecology and Management|volume=251|issue=3|pages=205–216|doi=10.1016/j.foreco.2007.06.005}}</ref>

According to a paper published in the journal ''[[Science (journal)|Science]]'', the number of natural and human-caused fires decreased by 24.3% between 1998 and 2015. Researchers explain this a transition from [[nomadism]] to settled lifestyle and intensification of [[agriculture]] that lead to a drop in the use of fire for land clearing.<ref>{{cite web|author=<!--Not stated-->|date=30 June 2017|title=Researchers Detect a Global Drop in Fires|url=https://earthobservatory.nasa.gov/IOTD/view.php?id=90493|url-status=live|archive-url=https://web.archive.org/web/20171208175626/https://earthobservatory.nasa.gov/IOTD/view.php?id=90493|archive-date=8 December 2017|access-date=4 July 2017|website=[[NASA Earth Observatory]]|df=dmy-all}}</ref><ref>{{cite journal|last1=Andela|first1=N.|last2=Morton|first2=D.C.|display-authors=etal|date=30 June 2017|title=A human-driven decline in global burned area|journal=[[Science (journal)|Science]]|volume=356|issue=6345|pages=1356–1362|bibcode=2017Sci...356.1356A|doi=10.1126/science.aal4108|pmc=6047075|pmid=28663495}}</ref>

Increases of certain tree species (i.e. [[conifers]]) over others (i.e. [[deciduous tree]]s) can increase wildfire risk, especially if these trees are also planted in [[monoculture]]s<ref>{{Cite web|title=Fires spark biodiversity criticism of Sweden's forest industry|url=https://phys.org/news/2018-07-biodiversity-criticism-sweden-forest-industry.html|website=phys.org}}</ref><ref>{{Cite web|title=The Great Lie: Monoculture Trees as Forests &#124; News & Views &#124; UNRISD|url=https://www.unrisd.org/80256B3C005BE6B5/(httpNews)/531DAFFB8B319F69C125792E00499ED1|website=www.unrisd.org}}</ref>
Some [[invasive species]], moved in by humans (i.e., for the [[pulp and paper industry]]) have in some cases also increased the intensity of wildfires. Examples include species such as [[Eucalyptus]] in California<ref>{{Cite web|title=Plant flammability list|url=https://www.state.sc.us/forest/scplants.pdf|access-date=10 January 2021}}</ref><ref>{{Cite web|title=Fire-prone plant list|url=https://www.firesafemarin.org/plants/fire-prone|url-status=dead|archive-url=https://web.archive.org/web/20180809183717/https://www.firesafemarin.org/plants/fire-prone|archive-date=9 August 2018|access-date=9 August 2018}}</ref> and [[gamba grass]] in Australia.

== Cultural aspects ==
Wildfires have a place in many cultures. "To spread like wildfire" is a common idiom in English, meaning something that "quickly affects or becomes known by more and more people".<ref name="spread like wildfire definition in the Cambridge English Dictionary">{{cite web | title=Spread Like Wildfire | website=definition in the Cambridge English Dictionary | url=https://dictionary.cambridge.org/us/dictionary/english/spread-like-wildfire | access-date=2020-09-21}}</ref> The [[Smokey Bear]] fire prevention campaign has yielded one of the most popular characters in the United States; for many years there was a living Smokey Bear mascot, and it has been commemorated on postage stamps.<ref>{{Cite web |author=Kathryn Sosbe |date=7 August 2014 |url=https://www.usda.gov/media/blog/2014/08/7/smokey-bear-iconic-symbol-wildfire-prevention-still-going-strong-70 |title=Smokey Bear, Iconic Symbol of Wildfire Prevention, Still Going Strong at 70 |website=USDA |language=en|access-date=2018-07-06}}</ref>

Wildfire activity has been attributed as a major factor in the development of [[Ancient Greece]]. In modern Greece, as in many other regions, it is the most common natural disaster and figures prominently in the social and economic lives of its people.<ref>{{cite journal|jstor=24707531|title=Fire and Society: A Comparative Analysis of Wildfire in Greece and the United States.|last1=Henderson|first1=Martha|last2=Kalabokidis|first2=Kostas|last3=Marmaras|first3=Emmanuel|last4=Konstantinidis|first4=Pavlos|last5=Marangudakis|first5=Manussos|journal=Human Ecology Review|year=2005|volume=12|issue=2|pages=169–182}}</ref>

In regards to communicating information to the public regarding wildfire safety, some of the most effective ways to communicate with others about wildfires are community outreach conducted through presentations to homeowners and neighborhood associations, community events such as festivals and county fairs, and youth programs.<ref name="auto">{{cite web | url = https://www.nifc.gov/PUBLICATIONS/communicators_guide/4%20Communication.PDF | title = National Wildfire Coordinating Group Communicator's Guide for Wildland Fire Management: Fire Education, Prevention, and Mitigation Practices | date = 26 June 2019 | place = District of Columbia | publisher = National Wildfire Coordinating Group | access-date = 15 November 2020 | archive-date = 25 January 2021 | archive-url = https://web.archive.org/web/20210125222444/https://www.nifc.gov/PUBLICATIONS/communicators_guide/4%20Communication.PDF | url-status = dead }}</ref>

== See also ==
{{Columns-list|colwidth=30em|
* [[Dry thunderstorm]]
* [[Fire-adapted communities]]
* [[Fire ecology]]
** [[Fire adaptations]]
* {{slink|HYSPLIT|Wildland fire smoke forecasting}}
* [[List of wildfires]]
** [[Bushfires in Australia]]
** [[Wildfires in the United States]]
* [[Pyrogeography]]
* [[Remote Automated Weather Station]]
* [[Wildland–urban interface]]
* Wildfire risk indexes:
** [[Forest fire weather index]] (Canada, France)
** [[Haines Index]]
** [[Keetch-Byram Drought Index]]
** [[McArthur Forest Fire Danger Index]]
** [[National Fire Danger Rating System]] (US)
* [[Women in firefighting]]}}
{{Clear}}

== References ==
{{reflist}}

=== Sources ===<!-- Please be careful when changing these templates, as the author last names or titles are used in the Citations section -->
{{Columns-list|colwidth=45em|
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'''Attribution'''
* {{NPS}}
* {{NIOSH}}

== External links ==
{{Scholia|topic}}
{{Sister project links |wikt=no|commons=Wildfire |b=Applied Ecology/Case Studies/Asian Rainforest Politics |n=no |q=no |s=The Encyclopedia Americana (1920)/Forest Fires |v=no |voy=Wildfires |species=no |d=no |display=Wildfires}}
* [https://earth.nullschool.net/#current/particulates/surface/level/annot=fires/overlay=pm1/winkel3 Current global map of hotspots (fires, volcanos, flare stacks), and fine particulates. Note that hotspot pixels do not indicate size.]

{{Firefighting}}
{{Forestry}}
{{Fire}}
{{Nature}}
{{Pollution}}
{{Authority control}}

[[Category:Wildfires| ]]
[[Category:Articles containing video clips]]
[[Category:Emergency management]]
[[Category:Fire prevention]]
[[Category:Types of fire]]
[[Category:Natural disasters]]
[[Category:Pollution]]
[[Category:Wildfire ecology]]
[[Category:Weather lore]]

Revision as of 01:46, 4 April 2023

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