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Wildfire

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For other uses, see Wildfire (disambiguation).
A daytime fire engulfing large trees
A wildfire on September 5, 2008

A wildfire is any uncontrolled fire that occurs in the countryside or wildland.[1][2] Other names such as brush fire, bushfire, forest fire, grass fire, hill fire, peat fire, vegetation fire, and wildland fire may be used to describe the same phenomenon. A wildfire differs from other fires by its extensive size; the speed at which it can spread out from its original source; its ability to change direction unexpectedly; and to jump gaps, such as roads, rivers and fire breaks.[3] Wildfires are characterized in terms of their physical properties such as speed of propagation; the combustible material present; the effect of weather on the fire; and the cause of ignition.[4]

Fossil records and human history contain accounts of wildfires, and wildfires occur on every continent except Antarctica and can be cyclical events.[5][6] Wildfires can cause extensive damage, both to property and human life (e.g. Black Saturday bushfires). Along with the damage caused, they also have various beneficial effects on wilderness areas, such as plant species that are dependent on the effects of fire for growth and reproduction.[5] However, large wildfires may have negative ecological effects.[4]

The strategies of prevention, detection, and suppression have varied over the years, but international conferences encourage "improved technology and research as weapons against wildfires around the world."[7] Current techniques may permit and even encourage smaller fires in some regions as a means of minimizing or removing sources of fuel from any wildfire that might develop.[8][9] While some wildfires burn in remote forested regions,[10] they can cause extensive destruction of homes and other property located in the wildland-urban interface: a zone of transition between developed areas and undeveloped wilderness.[8]

Characteristics

Wildfire behavior is often complex and variably dependent on factors such as fuel type, moisture content in the fuel, humidity, windspeed, topography,[11] geographic location, and ambient temperature.[12] While growth and behavior are unique to each fire due to many complex variables, the basic characteristics can be described as follows:[13][14]

Distinction from other fires

The name wildfire was once a synonym for Greek fire as well as a word for any furious or destructive conflagration.[2] Wildfires differ from other fires in that they take place outdoors in areas of grassland, woodlands, bushland, scrubland, peatland, and other woody materials that act as a source of fuel (or combustible material). Buildings are not usually involved, unless the fire spreads to adjacent communities and threatens these structures.

Africa with red and yellow markers where fires have been detected. A wide red band of markers runs east-west, just south of the Sahara Desert.
Distribution of wildfires on the African continent in 2002

Wildfires have a rapid forward rate of spread (FROS) when fueled by dense uninterrupted vegetation, particularly in wooded areas with canopies.[15] They can escalate as fast as 10.8 kilometers per hour (6.7 mph) in forests and 22 kilometers per hour (14 mph) in grasslands.[16] The ability of a wildfire's burning front to change direction unexpectedly and jump across fire breaks is another identifying characteristic. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire. These factors make fires particularly dangerous: in 1949 the Mann Gulch fire in Montana, U.S., thirteen smokejumpers died when they lost their communication links and became disorientated; the fire consumed 18 km² (4500 acres).[17] 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.[18]

While wildfires may be categorized as large, uncontrolled disasters that burn through 0.4 to 400 square kilometres (100 to 100,000 acres)* and higher,[19][20] wildfires can be as small as 0.25 acres (0.0010 km2) or less.[21] However, even though smaller events may be included in fire behavior analysis (see wildfire modeling),[22] most do not earn press attention,[23] which can be problematic considering that catastrophic wildfires and how they are portrayed by the media and viewed by the public influence public fire policies more so than small fires.[24][25]

Physical properties

See also: Fire § Chemistry, Fire control, Extreme weather, and Firestorm

Wildfires occur when the necessary elements of a fire triangle intersect: an ignition source is brought into contact with a combustible material such as vegetation, that is subjected to sufficient 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 required to evaporate any water within the material and heat the material to its fire point.[11] [3] Dense forests usually provide more shade, resulting in lower ambient temperatures and greater humidity.[26] 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.[27] Plants continuously lose water by evapotranspiration, but water loss is usually balanced by water absorbed from the soil, humidity, or rain.[28] When this balance is not maintained, plants dry out and are therefore more flammable, often a consequence of a long, hot, dry periods.[29][30]

A line of trees completely engulfed in flames. Towers with instrumentation are seen just beyond the fire's reach.
Experimental fire in Canada

A wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the smoldering transition between unburned and burned material.[31] 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 100 °C (212 °F). Next, the pyrolysis of wood at 230 °C (450 °F) releases flammable gases. Finally, wood can smolder at 380 °C (720 °F)[32] or, when heated sufficiently, ignite at 590 °C (1,000 °F).[33] Even before the flames of a wildfire arrive at a particular location, heat transfer from the wildfire front can precede the flames, warming the air to 800 °C (1,470 °F) and drying and pre-heating flammable materials.[34][35] High-temperature and long-duration surface wildfires may encourage flashover or torching: the drying of tree canopies and their subsequent ignition from below.[36]

Wildfires can advance tangential to the main front to form a flanking front, or burn opposite the direction of the main front by backing.[37] They may also spread by jumping or spotting, as winds and vertical convection columns carry hot wood embers called firebrands and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as firebreaks.[38][39] Torching and fires in tree canopies encourage spotting, and dry ground fuels that surround a wildfire are especially vulnerable to ignition from firebrands.[40] In Australian bushfires, spot fires have been documented "up to 10 kilometers (6 mi) ahead of the fire front."[41]

Especially large wildfires may affect air currents in their immediate vicinities by acting as natural chimneys. In an occurrence called a stack effect, air rises as it is heated, and large wildfires create powerful updrafts that will draw in new, cooler air from surrounding areas in thermal columns.[42] Great vertical differences in temperature and humidity encourage pyrocumulus clouds, strong winds, and fire whirls with the force of tornadoes at speeds of more than 80 kilometers per hour (50 mph).[43][44][45] Wide rates of spread, prolific crowning and/or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions.[46]

Fuel type

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, U.S.
Mountainous region with blackened soil and trees due to a recent fire.
Charred landscape following a crown fire in the North Cascades, U.S.

The spread of wildfires varies based on the flammable material present and its vertical arrangement.[47] Fuel density is governed by topography, as land shape determines factors such as available sunlight and water for plant growth. For example, fuels uphill from a fire are more readily dried and warmed by the fire than those downhill, yet burning logs can roll downhill. Overall, fire types can be generally characterized by their fuel as follows:[11][29][48][49][50]

  • Ground fires are fed by subterranean roots, duff and other buried organic matter. This fuel type is especially susceptible to ignition due to spotting. Ground fires typically burn by smoldering,[51] and can burn slowly for days to months,[52] such as peat fires in Kalimantan and East Sumatra, Indonesia, a result of a riceland creation project that unintentionally drained and dried the peat.[53] The thousands of underground coal fires that are burning around the world, such as those is Centralia, Pennsylvania and Burning Mountain, Australia, may also be considered ground fires.[54]
  • Crawling or surface fires are fueled by low-lying vegetation such as leaf and timber litter, debris, grass, and low-lying shrubbery.[55] Human-ignited ground-clearing fires can spread to the Amazon rain forest, damaging ecosystems not particularly suited for heat or arid conditions.[56]
  • Ladder fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and vines. Invasive plants such as Kudzu and Old World climbing fern that scale trees may also encourage ladder fires.[57]
  • Crown, canopy, or aerial fires devour suspended material at the canopy level, such as tall trees, vines, and mosses. The ignition of a crown fire is dependent on the density of the suspended material, canopy height, canopy continuity, and sufficient surface and ladder fires in order to reach the tree crowns.[58]

Effect of weather

Heat waves, droughts, cyclical climate changes such as El Niño, and other weather patterns can also increase the risk and alter the behavior of wildfires dramatically.[59] Years of precipitation followed by warm periods have encouraged more widespread fires and longer fire seasons.[60] Since the mid 1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season in the Western United States.[61]

Fire 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.[62] Sunlight warms the ground during the day and causes air currents to travel uphill, and downhill during the night as the land cools. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys.[63] Fires in Europe occur frequently during the hours of 12:00 p.m. and 2:00 p.m.[64] U.S. wildfire operations revolve around a 24-hour fire day that begins at 1000 hours due to the predictable increase in intensity resulting from the daytime warmth.[65]

Causes

The four major natural causes of wildfire ignitions are lightning, volcanic eruption, sparks from rockfalls, and spontaneous combustion.[66] Smoldering underground coal fires can also flare up and ignite nearby flammable material.[67] However, many wildfires are attributed to human sources such as arson, discarded cigarettes, sparks from equipment,[68] and power line arcs that may be detected by arc mapping.[69] In societies experiencing shifting cultivation where land is cleared quickly and farmed until the soil loses fertility, slash and burn clearing is often considered the least expensive way to prepare land for future use.[70][71] Forested areas cleared by logging encourages the dominance of flammable grasses, and abandoned logging roads overgrown by vegetation may act as fire corridors. Annual grassland fires in South Vietnam can be attributed in part to the destruction of forested areas by herbicides, explosives, and mechanical land clearing and burning operations during the Vietnam War.[72]

History

Fossil record

Main article: Fossil record of fire

Template:Origin of fire

Human history

See also: Deforestation § Historical causes, History of firefighting, History of wildfire suppression, and List of wildfires

From minor allusions in the Bible to classical writers such as Homer, wildfires have been mentioned in human history, "but usually in a general way: they were not much interested in the uncultivated roughlands where fires occur."[73][74] Wildfires were also used in battles throughout 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 14th century Sardinia, firebreaks were used for wildfire protection. Phillip II of Spain in the 1550s "discouraged pasturage in certain provinces on the grounds that evils were caused by fires."[73][74] In the countries bordering the Baltic Sea, fire in land use systems was typical during the Neolithic period until World War II.[75] In the Atlantic Ocean on the island of Madeira, fire was used to clear the land of Laurisilva (laurel forest) in 1419.[76]

Wildfires typically occurred during periods of increased temperature and drought; 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 B.C. and 1660 A.D. can be attributed to human influence.[77] "Sedimentological and stratigraphic properties of several alluvial fans in the northeastern" Yellowstone National Park found "a major pulse of fire-related debris-flow between AD 1050 and 1200, which... 'coincided with the height of the widely recognized Medieval Warm Period.'"[78]

Ecology

Main article: Fire ecology
See also: Disturbance (ecology) and Forestry
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 pine forest next to Hara Bog, Lahemaa National Park, Estonia. The pictures were taken one and two years after the fire.

Wildfires are common in climates that are sufficiently moist to allow the growth of vegetation but feature extended dry, hot periods.[5]Such places include the vegetated areas of Australia and south east Asia, the veld in the interior and the fynbos in the Western Cape of South Africa, and the forested areas of the United States and Canada. Fires can be particularly intense during days of strong winds and periods of drought.[79] Fire prevalence is also high during the summer and autumn months, when fallen branches, leaves, grasses, and scrub dry out and become more flammable.[80][81] Global warming may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires.[4][82][83]

Many ecosystems are suffering 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 areas has caused the elimination of native plant communities and have replaced them with non-native weeds.[84][85] Invasive species such as Lygodium microphyllum and Bromus tectorum may create a positive feedback loop, increasing fire frequency even more.[57][86] In the Amazon rain forest, drought, logging and cattle ranching pratices, and slash-and burn agriculture damage fire-resistant forests and promote the growth of flammable brush, creating a cycle that encourages more burning.[87] Fires in the rain forest threaten "a treasure trove of species diversity and, if burned, [will produce] a large source carbon dioxide emissions"[88] and threaten to "clear or severely damage 55 per cent of the Amazon rainforest by the year 2030."[89] Wildfires generate ash, destroy available organic nutrients, and cause an increase in water runoff, eroding away other nutrients and creating flash flood conditions.[90][91] A wildfire in the North Yorkshire Moors, on September 17, 2003, destroyed some 2.5 square kilometres (600 acres)* of heather and the underlying peat layers. Wind erosion stripped the ash and the exposed soil, revealing archaeological remains dating back to 10,000 BC; however continuing erosion of the burnt moorland threatened these remains. The burnt moorland was stabilized by sowing ryegrass and heather seeds to allow the heather to regenerate.[92] 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.[93]

Plant adaptations

Template:Details3

Sloping surface containing green vegetation with purple flowers. Trees are seen in the background.
Fireweed, an example of a pioneer species that quickly colonizes an area after a wildfire

Wilderness areas, especially those in North America, are now considered fire-dependent, and previous policies of complete suppression are believed to have upset natural cycles (see history of wildfire suppression)[94][80] and increased fuel loads and the amount of fire intolerant vegetation.[95] In the absence of human intervention, certain organisms in these ecosystems survive through adaptations to fire regimes. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate competition. Dense bark, shedding lower branches, and high water content in external structures may protect the organisms from rising temperatures.[5] Fire-resistant seeds and reserve shoots that sprout after a fire encourage species preservation (see pioneer species). Smoke, charred wood, and heat are common fire cues that stimulate the germination of seeds (see serotiny).[96] Exposure to smoke from burning plants promotes germination in other types of plants by inducing the production of the orange butenolide.[97] Grasslands in Western Sabah, Malaysian pine forests, and Indonesian Casuarina forests are believed to have resulted from previous periods of fire.[98] Plants of the genus Eucalyptus contain flammable oils that encourage fire[99] and hard sclerophyll leaves to resist heat and drought, ensuring their dominance over less fire-tolerant species.[100] Chamise deadwood litter is low in water content and flammable, and the shrub quickly sprouts after a fire.[5] Sequoia rely on periodic fires to reduce competition, release seeds from their cones, and clear the soil and canopy for new growth.[101]

Atmospheric effects

See also: Air pollution, Atmospheric chemistry, Haze, 1997 Southeast Asian haze, 2005 Malaysian haze, and 2006 Southeast Asian haze
A paved road with trees and grasses on the side with a large, white and dark gray smoke could rising in the distance.
A Pyrocumulus cloud produced by a wildfire in Yellowstone National Park

Most of the Earth's weather and air pollution reside in the troposphere, the part of the atmosphere that extends from the surface of the planet to a height of between 8 and 13 kilometers (5 and 8 mi). A severe thunderstorm or pyrocumulonimbus in the area of a large wildfire can have its vertical lift enhanced to boost smoke, soot and other particulate matter as high as the lower stratosphere.[102] Previously, it was thought that most particles in the stratosphere came from volcanoes, but smoke and other wildfire emissions have been detected from the lower stratosphere.[103] Pyrocumulus clouds can reach 20,000 feet (6,100 m) over wildfires.[104] With an increase in fire byproducts in the stratosphere, ozone concentration was three times more likely to exceed health standards.[105] Satellite observation of smoke plumes from wildfires revealed that the plumes could be traced intact for distances exceeding 1,600 kilometres (990 mi)*.[106] Computer-aided models (e.g. CALPUFF) may help predict the size and direction of wildfire-generated smoke plumes (see atmospheric dispersion modeling).[107]

Wildfires can affect climate and weather and have major impacts on regional and global pollution.[108] Wildfire emissions contain greenhouse gases and a number of criteria pollutants which can have a substantial impact on human health and welfare.[109] Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigatonnes (0.89 and 2.83 billion short tones) of CO2 into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels.[110][111] Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15%.[112]

Panorama of a hilly expanse featuring a large smoke trail covering more than half of the visible sky.
Smoke trail from a fire seen while looking towards Dargo from Swifts Creek, 11 January 2007

Prevention

See also: Control of fire by early humans and Fire protection
Drawing of a grizzly bear with human features. He is wearing blue jeans with a belt and a brimmed hat with the name "Smokey" on the cap, and has a shovel in his left hand. He is pointing to the viewer while the text "Only You" is seen below him.
1985 Smokey Bear poster

Wildfire prevention "involves all measures that impede the outbreak of fire or reduce its severity and spread."[113] Effective prevention techniques allow supervising agencies to manage air quality, maintain ecological balances, protect resources,[114] as well as limiting the effects of future uncontrolled fires.[115] North American firefighting policies may permit naturally-caused fires to burn to maintain their ecological role, so long as the risks of escape onto high-value areas are mitigated.[116] However, prevention policies must consider the role that humans play in wildfires, since, for example, only 5% of forest fires in Europe are not related to human involvement.[117] Sources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture (for example, slash-and-burn farming in Southeast Asia).[118] Landholders with "fire-sensitive investments" such as orchards and tree crops may encourage other landholders to reduce fire risks.[119]

In the mid-1800s, explorers from the HMS Beagle observed Australian Aborigines using fire for ground clearing, hunting, and regeneration of plant food (see fire-stick farming).[120] Such careful use of fire has been employed for centuries in the Kakadu National Park to encourage biodiversity.[121] In 1937, US 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, leaders of the Axis powers of World War II, characters from the Disney movie Bambi, and lastly Smokey Bear.[122]

File:Image-DSCF0013.JPG
A prescribed burn in a Pinus nigra stand in Portugal

Wildfires are a combination of factors such as topography, fuels, and weather. Other than reducing human infractions, only fuels may be altered to affect future fire risk and behavior.[123] Wildfire prevention programs around the world may employ techniques such as wildland fire use and prescribed burns (controlled burns).[1][124][125] 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.[126] Vegetation may be burned periodically to maintain high species diversity,[127] and frequent burning of surface fuels limits fuel accumulation, thereby reducing the risk of crown fires.[128] Using strategic cuts of trees, fuels may also be removed by handcrews in order to clean and clear the forest, prevent fuel build-up, and create access into forested areas.[129] Chain saws and large equipment can be used to thin out ladders fuels and shred trees and vegetation to a mulch.[130] Multiple fuel treatments are often needed to influence future fire risks,[131] and wildfire models may be used to predict and compare the benefits of different fuel treatments on future wildfire spread. However, controlled burns are reportedly "the most effective treatment for reducing a fire’s rate of spread, fireline intensity, flame length, and heat per unit of area."[132] Additionally, while fuel treatments are typically limited to smaller areas, effective fuel management requires the administration of fuels across large landscapes in order to reduce future fire size and severity.[133]

Building codes in fire-prone areas typically require that structures be built of flame-resistant materials[134] and a defensible space be maintained by clearing flammable materials within a prescribed distance from the edifice.[135] Communities in the Philippines also maintain fire lines 5 to 10 meters (16 to 33 ft) wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather.[136]

Three photos of the same forest region. The first features a central tree with other trees in the distance. A man and two mounted horses are seen at varying distances behind the central tree. The forest floor features low-lying vegetation such as grasses. The second and third photos feature the same central tree but with increasing amounts of trees in the mid- and foregrounds. The central tree is almost completely blocked from view in the third picture.
A ponderosa pine stand in the Bitterroot National Forest in Montana in 1909, 1948, and 1989. "Note the changes in vertical arrangement and horizontal continuity in forest stand structure", a result of fire prevention efforts since 1895.[137]

Detection

See also: Remote sensing
A four-legged tower with a small enclosure 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.[138] Early detection efforts were focused on early response, accurate day and nighttime use, the ability to prioritize fire danger, and fire size and location in relation to topography. Fire lookout towers were used in the United States in the early 1900s and fires were reported using telephones, carrier pigeons, and heliographs.[139] Aerial and land photography using instant cameras were used in the 1950s until 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 fire manager. During the Yellowstone fires of 1988, a data station was established in West Yellowstone, permitting fire information delivery in approximately four hours.[140]

Currently, public hotlines, fire lookouts 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 operator fatigue (see asthenopia), 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. These systems may be semi- or fully-automated and employ systems based on the risk area and degree of human presence, as suggested by GIS data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via GPS into a collective whole for near-realtime use by wireless Incident Command Centers.[141][142]

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)

A small, high risk area (thick vegetation, strong human presence or close to critical urban area) can be monitored using a local sensor network. Detection systems may include wireless sensor networks that act as automated weather systems: detecting temperature, humidity, and smoke.[143][144][145] These may be battery-powered, solar-powered, or tree-rechargeable: able to recharge their battery systems using the small electrical currents in plant material.[146] Larger, medium-risk areas could 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." Brightness and color change detection as well as night vision capabilities may be incorporated also into sensor arrays.[147][148][149]

High-altitude view of a mountain range with white-brown smoke billowing from several sources across the range
The Old Fire burning in the San Bernardino Mountains (image taken from the International Space Station)

Satellite and aerial monitoring 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.[150][151] Satellite-mounted sensors such as Envisat's AATSR and ERS-2's ATSR can measure infrared radiation emitted by fires, identifying hot spots greater than 39 °C (102 °F).[152][153] The NOAA's Hazard Mapping System combines remote-sensing data from satellite sources such as GOES, MODIS, and AVHRR for detection of fire and smoke plume locations (see 2006 Southeast Asian haze#Imagery).[154][155] However, satellite detection is prone to offset errors, anywhere from 2 to 3 kilometers (1 to 2 mi) for MODIS and AVHRR data and up to 12 km (7.5 mi) for GOES data.[156] 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 and may also limit the effectiveness of satellite imagery.[157]

Suppression

Main article: Wildfire suppression
See also: Firefighting
A three-engine red-and-white cargo plane in-flight, releasing a large quantity of water from its undercarriage storage tanks. The water trails behind the aircraft in a continuous, fan-shaped drop pattern.
Tanker 910 during a drop demonstration in December, 2006

Wildfire suppression may include a variety of tools and technologies, including throwing sand and beating fires with sticks and palm fronds in rural Thailand,[158] using silver iodide to encourage snow fall in China,[159] and full-scale aerial assaults by ALTUS II unmanned aerial vehicles,[160] planes, and helicopters using drops of water and fire retardants.[161] 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 can cause extensive damage. Worldwide damage from wildfires is in the billions of euros annually.[162] Wildfires in the United States are responsible for "about 95% of the total acres burned and close to 85% of all suppression costs,"[163][164] as suppression efforts and damage caused can exceed billions of US dollars annually.[165][166][167] Yearly fires in Canada consume an average of 25,000 square kilometers (6,200,000 acres)[168] and in the US an average of 29,500 square kilometers (7,300,000 acres).[169]

Fuel buildup can result in costly, devastating fires as more new houses and ranches are built adjacent to wilderness areas (see rural-urban fringe). Continued growth in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism.[170] However, the population growth along the wildland-urban interface discourages the use of current fuel management techniques. Smoke is an irritant and attempts to thin out the fuel load is met with opposition due to desirability of forested areas, in addition to other wilderness goals such as endangered species protection and habitat preservation.[171] The ecological benefits of fire is often overridden by the economic benefits of protecting structures and lives.[167] Additionally, government policies that cover the wilderness usually differs from local and state policies that govern urban lands.[172][173]

Modeling

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 start". 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

Wildfire modeling is concerned with numerical simulation of wildfires in order to understand and predict fire behavior.[174][175] Wildfire modeling can ultimately aid wildfire suppression, namely increase the safety of firefighters and the public, reduce risk, 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 windspeed 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.[176][177] However, large fires that exceed suppression capabilities are often regarded as statistical outliers in these analyses (see extreme value theory), even though fire policies are influenced by catastrophic wildfires more so than small fires.[178]

See also

2

Notes

  1. ^ a b Federal Fire and Aviation Operations Action Plan, 4.
  2. ^ a b Wildfire, Cambridge University Press, retrieved 2009-07-14
  3. ^ a b The Science of Wildland fire, National Interagency Fire Center, retrieved 2008-11-21
  4. ^ a b c Flannigan, M.D. (2005), "Forest Fires and Climate Change in the 21st century" (PDF), Mitigation and Adaptation Strategies for Global Change, 11: 847, doi:10.1007/s11027-005-9020-7, retrieved 2009-06-26 {{citation}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ a b c d e Stephen J. Pyne, How Plants Use Fire (And Are Used By It), NOVA online, retrieved 2009-06-30
  6. ^ Krock, Lexi (June 2002), The World on Fire, NOVA online (PBS), retrieved 2009-07-13
  7. ^ International Experts Study Ways to Fight Wildfires, VOA News, 2009-06-24, retrieved 2009-07-09
  8. ^ a b Interagency Strategy for the Implementation of the Federal Wildland Fire Policy, entire text
  9. ^ National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, entire text
  10. ^ Wildfires in Canada, Government of Canada, 2009-02-04, retrieved 2009-07-09
  11. ^ a b c National Wildfire Coordinating Group Fireline Handbook, Appendix B: Fire Behavior (PDF), National Wildfire Coordinating Group, April, 2006, retrieved 2008-12-11 {{citation}}: Check date values in: |date= (help)
  12. ^ Graham, et al., 12.
  13. ^ National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, 4-6.
  14. ^ Graham, et al., 12.
  15. ^ Protecting Your Home From Wildfire Damage (PDF), Florida Alliance for Safe Homes (FLASH), retrieved 2009-07-14
  16. ^ Billing, 5-6
  17. ^ Rothermel, Richard C. (May 1993), General Technical Report INT-GTR-299 - Mann Gulch Fire: A Race That Couldn't Be Won, United States Department of Agriculture, Forest Service, Intermountain Research Station, retrieved 2009-06-26
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References

2

External links

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