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Wildfire

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For other uses, see Wildfire (disambiguation).
Bitterroot National Forest wildfire

A wildfire, also known as a forest fire, vegetation fire, grass fire, brush fire, peat fire ("gambut" in Indonesia), bushfire (in Australasia), or hill fire, is an uncontrolled fire often occurring in wildland areas, but which can also consume houses or agricultural resources. Common causes include lightning, human carelessness, arson, volcano eruption, and pyroclastic cloud from active volcano.

El Niño (weather pattern disturbance), heat wave and drought are major contributors to extreme forest fires.

The word "wildfire" originated as a synonym for Greek fire, a napalm-like substance used in medieval Europe as a naval weapon; the word attained its present meaning by a common misunderstanding of the expression "spread like wildfire".

Background

Green Knoll Wildfire in Jackson, Wyoming
After the 2003 wildfire at Glacier National Park

Wildfires are common in many places around the world, including much of the vegetated areas of Australia, 'veld' in the interior and 'fynbos' in the Western Cape of South Africa, forest areas of the United States and Canada, where the climates are sufficiently moist to allow the growth of trees, but feature extended dry, hot periods particularly in the Summer,fall, and in time of drought when fallen branches, leaves, and other material can dry out and become highly flammable. Wildfires are also common in grasslands and scrublands. Wildfires tend to be most common and severe during years of drought and occur on days of strong winds. With extensive urbanization of wildlands, these fires often involve destruction of suburban homes located in the wildland urban interface, a zone of transition between developed areas and undeveloped wildland.

Today it is accepted that wildfires are a natural part of the ecosystem of wildlands, where, at the least, plants have evolved to survive fires by a variety of strategies (from possessing reserve shoots that sprout after a fire, to fire-resistant seeds), or even encourage fire (for example eucalypts contain flammable oils in the leaves) as a way to eliminate competition from less fire-tolerant species. In 2004, researchers discovered that exposure to smoke from burning plants actually promotes germination in other types of plants by inducing the production of the chemical butenolide. Most native animals, too, are adept at surviving wildfires.

Charred landscape following a fire in the North Cascades.

On occasions, wildfires have caused large-scale damage to private or public property, destroying many homes and causing deaths, particularly when they have reached urban-fringe communities.

Slash (small, rotten, misshapen, or otherwise undesirable wood discarded during logging) has historically provided the fuel for devastating fires such as the fires in Michigan in the 19th century.

The aftermath of a wildfire can be as disastrous if not more so than the fire. A particularly destructive fire burns away plants and trees that prevent erosion. If heavy rains occur after such a fire, landslides, ash flows, and flash floods can occur. This can result in property damage outside the immediate fire area, and can affect the water quality of streams, rivers and lakes. Wildfires burned long before humans evolved. One main component of Carboniferous north hemisphere coal is charcoal left over by forest fires. The earliest known evidence of a wildfire dates back to Late Devonian period (about 365 million years ago) [1].

Aftermath of the 1988 Yellowstone Wildfire, seen at Fountain Flat Drive

Behavior

A massive forest fire

When the water reserves in the soil are between 100% and 30%, the evaporation of water in plants is balanced by water absorbed from the soil. Below this threshold, the plants dry out and under stress release the flammable gases ethane and ethylene. A consequence of a long hot and dry period is therefore that the air contains flammable essences and plants are drier and highly flammable.

The propagation of the fire has three mechanisms:

  • "crawling" fire: the fire spreads via low level vegetation (e.g., bushes)
  • "crown" fire: a fire that "crowns" (spreads to the top branches of trees) can spread at an incredible pace through the top of a forest. Crown fires can be extremely dangerous to all inhabitants underneath, as they may spread faster than they can be outrun, particularly on windy days. (see Firestorm)
  • "jumping" or "spotting" fire: burning branches and leaves are carried by the wind and start distant fires; the fire can thus "jump" over a road, river, or even a firebreak.

The Nevada Bureau of Land Management identifies several different wildfire behaviors. For example, extreme fire behavior includes wide rates of spread, prolific crowning and/or spotting, the presence of fire whirls, or a strong convection column. Extreme wildfires behave erratically and unpredictably.

In southern California, under the influence of Santa Ana winds, wildfires can move at tremendous speeds, up to 40 miles (60 km) in a single day, consuming up to 1,000 acres (4 km²) per hour. Dense clouds of burning embers push relentlessly ahead of the flames crossing firebreaks without pause.

Propagation of the fire with a characteristic shape of a "pear"

The powerful updraft caused by a large wildfire will draw in air from surrounding areas. These self-generated winds can lead to a phenomenon known as a firestorm.

French models of wildfires dictate that a fire's front line will take on the characteristic shape of a pear; the major axis being aligned with the wind. In the case of the fires in southeastern France, the speed of the fire is estimated to be 3% to 8% of the speed of the wind, depending on the conditions (density and type of vegetation, slope). Other models predict an elliptical shape when the ground is flat and the vegetation is homogeneous.

Another type of wildfire is the smouldering fire. It involves the slow combustion of surface fuels without generating flame, spreading slowly and steadily. It can linger for days or weeks after flaming has ceased, resulting in potential large quantities of fuel consumed and becoming a global source of emissions to the atmosphere. It heats the duff and mineral layers, affecting the roots, seeds and plant stems at the ground.

Since 1997, in Kalimantan and East Sumatra, Indonesia, there is a type of continous smouldering fire on the peat bogs that burn underground for years without any supply of oxygen. The underground fire ignited new forest fire each year during dry season.

Prevention

Forest fire danger level (Los Alamos, New Mexico). When danger level is Extreme, a red flag is flown.

For many decades the policy of the United States Forest Service was to suppress all fires, and this policy was epitomized by the mascot Smokey Bear and was also the basis of parts of the movie Bambi. The policy began to be questioned in the 1960s, when it was realized that no new Giant Sequoia had been grown in the forests of California, because fire is an essential part of their life cycle. This produced the policy of controlled burns to reduce underbrush. This clears much of the undergrowth through forest and woodland areas, making travel and hunting much easier while reducing the risk of dangerous high-intensity fires caused by many years of fuel buildup.

The previous policy of absolute fire suppression in the United States has resulted in the buildup of fuel in some ecosystems such as dry ponderosa pine forests. However, this concept has been misapplied in a "one-size-fits-all" application to other ecosystems such as California chaparral. Fire suppression in southern California has had very little impact over the past century. The amount of land burned in 6 southern California counties has been relatively unchanged. In fact, fire frequency has been increasing dramatically over the past century in lock step with population growth. Urbanization can also result in fuel buildup and devastating fires, such as those in Los Alamos, New Mexico, East Bay Hills, within the California cities of Oakland and Berkeley between October 19 and 22, 1991, all over Colorado in 2002, and throughout southern California in October 2003. Homes designed without considering the fire prone environment in which they are built have been the primary reason for the catastrophic losses experienced in wildfires.

On average, wildfires burn 4.3 million acres (17,000 km²) in the United States annually. In recent years the federal government has spent $1 billion a year on fire suppression. 2002 was a record year for fires with major fires in Arizona, California, Colorado, and Oregon.

The risk of major wildfires can be reduced partly by a reduction of the amount of fuel present. In wildland, this can be accomplished by either conducting controlled burns, deliberately setting areas ablaze under less dangerous weather when conditions are less volatile or physical fuel removal by removing some trees as is conducted in many American forests. Such techniques are best used within the wildland/urban interface where communities connect with wild open space. Prescribed burns in the backcountry, away from human habitations, are not particularly effective in preventing large fires. All the large catastrophic fires in the United States have been wind driven events where the amount of fuel (trees, shrubs, etc.) has not been the most important factor in fire spread.

People living in fire-prone areas typically take a variety of precautions, including building their homes out of flame-resistant materials, reducing the amount of fuel near the home or property (including firebreaks, their own miniature control lines, in effect), and investing in their own firefighting equipment.

Rural farming communities are rarely threatened directly by wildfire. These types of communities are usually located in large areas of cleared, usually grazed, land, and in the drought conditions present in wildfire years there is often very little grass left on such grazed areas. Hence the risk is minimized. However, urban fringes have spread into forested areas, for example in Sydney and Melbourne, and communities have literally built themselves in the middle of highly flammable forests. In Cape Town, the city lies on the fringe of the Table Mountain National Park. These communities are at high risk of destruction in bushfires, and should take extra precautions.

There are quite a few US states, Canadian provinces and many countries around the world that still use Fire lookouts as a means of early detection of forest fires. Some nations still using this system besides the US and Canada include: Israel, Latvia, France, Germany, Italy, Spain, Portugal, Brazil, Uruguay, New Zealand and Australia.

Fire suppression

Main article: fire suppression
An Air National Guard C-130 Hercules drops fire retardant on wildfires in Southern California

Wildland fire suppression is a unique aspect of firefighting. Most fire-prone areas have large firefighter services to help control bushfires. As well as the water-spraying fire apparatus most commonly used in urban firefighting, bushfire services use a variety of alternative techniques. Typically, forest fire fighting organizations will use large crews of 20 or more people who travel in trucks to the fire. These crews use heavier equipment to construct firebreaks, and are the mainstay of most firefighting efforts. Other personnel are organized into fast attack teams typically consisting of 5–8 people. These fast attack teams are helicoptered into smaller fires or hard to reach areas as a preemptive strike force. They use portable pumps to douse small fires and chainsaws to construct firebreaks or helicopter landing pads if more resources are required. Hand tools are commonly used to construct firebreaks and remove fuels around the perimeter of the fire to halt its spread, including shovels, rakes, and the pulaski, a tool unique to wildland firefighting. In the eastern United States, portable leaf blowers are sometimes used. In the western United States, large fires often become extended campaigns, and temporary fire camps are constructed to provide food, showers, and rest to fire crews. These large fires are often handled by 20 person hand crews, sometimes known as hotshot crews, specially organized to travel to large fires.

Fast attack teams are often considered the elite of firefighting forces, as they sometimes deploy in unusual ways. If the fire is on a particularly steep hill or in a densely wooded area, they may rappel or fast-rope down from helicopters. If the fire is extremely remote, firefighters known as smokejumpers may parachute into site from fixed-wing aircraft. In addition to the aircraft used for deploying ground personnel, firefighting outfits often possess helicopters and water bombers specially equipped for use in aerial firefighting. These aircraft can douse areas that are inaccessible to ground crews and deliver greater quantities of water and/or flame retardant chemicals. Managing all of these various resources over such a large area in often very rugged terrain is extremely challenging, and often the Incident Command System is used. As such, each fire will have a designated Incident Commander who oversees and coordinates all the operations on the fire. This Incident Commander is ultimately responsible for the safety of the firefighters and for the success of firefighting efforts.

A helicopter dips its bucket into a pool before returning to drop the water on a wildfire outside of Naples, Italy.

Large fires are of such a size that no conceivable firefighting service could attempt to douse the whole fire directly, and so alternative techniques are used. In alternative approaches, firefighters attempt to control the fire by controlling the area that it can spread to, by creating "control lines", which are areas that contain no combustible material. These control lines can be produced by physically removing fuel (for instance, with a bulldozer), or by "backfiring", in which small, low-intensity fires are started, using a device such as the driptorch, or pyrotechnic flares known as "fusees", to burn the flammable material in a (hopefully) controlled way. These may then be extinguished by firefighters or, ideally, directed in such a way that they meet the main fire front, at which point both fires run out of flammable material and are thus extinguished.

The Old Fire burning in the San Bernardino Mountains (image taken from the International Space Station)
Plowing a fire lane in advance of a forest wildfire, Georgetown, South Carolina

Unfortunately, such methods can fail in the face of wind shifts causing fires to miss control lines or to jump straight over them (for instance, because a burning tree falls across a line, burning embers are carried by the wind over the line, or burning tumbleweeds cross the line).

The actual goals of firefighters vary. Protection of life (those of both the firefighters and "civilians") is given top priority, then private property according to economic and social value and also to its "defendibility" (for example, more effort will be expended on saving a house with a tile roof than one with a wooden-shake roof). In very severe, large fires, this is sometimes the only possible action. Protecting houses is regarded as more important than, say, farming machinery sheds, although firefighters, if possible, try to keep fires off farmland to protect stock and fences (steel fences are destroyed by the passage of fire, as the wire is irreversibly stretched and weakened by it). Preventing the burning of publicly owned forested areas is generally of least priority, and, indeed, it is quite common (in Australia, at least) for firefighters to simply observe a fire burn towards control lines through forest rather than attempt to put it out more quickly; it is, after all, a natural process. On any incident, ensuring the safety of firefighters takes priority over fire suppression. When arriving on a scene a fire crew will establish a safety zone(s), escape routes, and designate lookouts (known by the acronym LCES, for lookouts, communications, escape routes, safety zones). This allows the firefighters to engage a fire with options for a retreat should their current situation become unsafe. In addition all fire suppression activities are based from an "anchor point" (such as lake, rock slide or road). From an anchor point firefighter can work to contain a wildland fire without the fire outflanking them. As last resort, all wildland firefighter carry a fire shelter. In a unescapable burnover situation the shelter will provide limited protection from radiant and convective heat, as well as superheated air. As such a greater emphasis is placed on safety and preventing entrapment, and is reinforced with a list of 10 fire orders and 18 "watch out situations" for firefighters to be aware of, which warn of potentially dangerous conditions.

In North America, the belief that fire suppression has substantially reduced the average annual area burned is widely held by resource managers and is often thought to be self-evident. However, this belief has been the focus of vocal debate in the scientific literature recently. Direct empirical evidence of the effects of fire suppression in boreal forest ecosystems began with two studies by Stocks (1991) and Ward and Tithecott (1993), that used Ontario government fire records to make comparisons of average annual area burned between areas with and without aggressive fire suppression policies. Numerous subsequent studies have been done, often presenting similar information (Martell 1994, Martell 1996, Weber & Stocks 1998, Li 2000, Ward & Mawdsley 2000). The proponents of these studies argue that areas without aggressive fire suppression policies have larger average fire sizes and greater average annual area burned and a longer interval between fires and that this is evidence of the effect of fire suppression. The most recent work in this area of analysis is Ward et al. (2001).

Several recent papers have argued against this idea (Johnson et al. 2001, Miyanishi & Johnson 2001, Miyanishi et al. 2002, Bridge et al. 2005). These papers claim that statistically rigorous techniques for estimating the average annual area burned, called the fire cycle, do not show changes in the fire cycle associated with fire suppression and that the evidence used to support the effect of fire suppression is biased and has been presented in a way that is flawed. Note that none of these papers criticize fire management agencies for being anything less than completely committed to their mandate. Nor do they suggest that fire personnel are not well trained, efficiently deployed or well managed. Instead, these papers simply suggest that despite the resources employed, fire management agencies are simply unable to effectively reduce the average annual area burned.

Recently, Cumming (2005) used novel approaches to analyze multiple components of fire management activity in greater detail than previously done, and confirmed the effectiveness of fire suppression.

A new material called "gel" (made from super-absorbent polymer) is used in California, USA for fighting forest fire. Water is soaked up by the gel and stored in layers of tiny bubbles. The gel can protect tree/house for longer time than ordinary water, because it get boiled by fire one layer at a time.

Atmospheric effects

Wildfires burn areas of Portuguese forest every year, obscuring the Sun in smoke.

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. A severe thunderstorm or pyro-cumulonimbus in the area of a large wildfire can have its vertical lift enhanced to boost smoke, soot and other particles as high as the lower stratosphere (Wang, 2003).

Previously, it was thought that most particles in the stratosphere came from volcanoes or were generated by high-flying aircraft. Collection of air samples from the stratosphere in 2003 led to detection of carbon monoxide and other gasses related to combustion at a level 30 times higher than can be accounted for by commercial aircraft.

Satellite observation of smoke plumes from wildfires revealed that the plumes could be traced intact for distances exceeding 5,000 kilometers. This observation suggests that the plumes were in the stratosphere above weather conditions that would have brought the plume back to earth.

Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15% (Baumgardner, et al., 2003).

The massive forest fire in Indonesia (1997/1998) released approx. 2.57 gigatonnes of Carbon Dioxide into the atmosphere (source: Nature magazine, November 2002). During 1997-1998, the total amount of Carbon Dioxide released to the atmosphere was 6 gigatonnes. Most of the Carbon Dioxide gas is released by the continous underground smouldering fire on the peat bogs.

After the end of a wildfire, houses sometimes experience an ember attack - an onslaught of burning twigs or branches that can ignite a fire in the house.

Statistics

Every year, the burnt surface represents about:

  • France: 211 km², 52,140 acres, 0.04% of the territory
  • Portugal:
    • 1991 : 1,820 km², 449,732 acres, i.e. 2% of the territory
    • 2003 : 4,249 km², 1.05 million acres, i.e. 4.6% of the territory; 20 deaths ;
    • 2004 : 1,205 km², 297,836 acres, i.e. 1.3% of the territory
    • 2005 : 2,864 km², 707,668 acres, i.e. 3.1% of the territory; 17 deaths;
    • 2006 : 724 km², 178,904 acres, i.e. 0.8% of the territory; 10 deaths;
  • United States: 17,400 km², 4.3 million acres i.e. 0.18% of the territory
  • Indonesia. Sources: before 1997 from Indonesian Environmental Impact Management Agency (BAPEDAL) and Canadian International Development Agency (CIDA) - Collaborative Environmental Project in Indonesia (CEPI). 1997/1998 from Asian Development Bank (ADB). From 1999: Indonesian Ministry of Forestry.
    • 1982 and 1983: 36,000 km² (8.9 million acres)
    • 1987: 492 km² (121.880 acres).
    • 1991: 1.189 km² (293.761 acres).
    • 1994: 1.618 km² (399.812 acres).
    • 1997 and 1998: 97,550 km² (24.1 million acres) - from ADB.
    • 1999: 440.90 km² (108,949 acres).
    • 2000: 82.55 km² ( 20,399 acres).
    • 2001: 143.51 km² ( 35,462 acres).
    • 2002: 366.91 km² ( 90,665 acres).
    • 2003: 37.45 km² ( 9,254 acres).
    • 2004: 139.91 km² ( 34,573 acres).
    • 2005: 133.28 km² ( 32,934 acres).

See also

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References

  • Baumgardner, D., et al. 2003. Warming of the Arctic lower stratosphere by light absorbing particle. American Geophysical Union fall meeting. Dec. 8-12. San Francisco.
  • Bridge, S.R.J, K. Miyanishi and E.A. Johnson. 2005. A Critical Evaluation of Fire Suppression Effects in the Boreal Forest of Ontario. Forest Science 51:41-50.
  • Cumming, S.G. 2005. Effective fire suppression in boreal forests. Can. J. For. Res. 35: 772–786.
  • Fromm, M., et al. 2003. Stratospheric smoke down under: Injection from Australian fires/convection in January 2003. American Geophysical Union fall meeting. Dec. 8-12. San Francisco.
  • Johnson, E.A. and Miyanishi K. (Eds.) 2001. Forest Fires - Behavior and Ecological Effects. Academic Press, San Diego.
  • Johnson, E.A., K. Miyanishi, and S.R.J. Bridge. 2001. Wildfire regime in the boreal forest and the idea of suppression and fuel buildup. Conserv. Biol. 15:1554-1557.
  • Li, C. 2000. Fire regimes and their simulation with reference to Ontario. P. 115-140 in Ecology of a managed terrestrial landscape: patterns and processes of forest landscapes in Ontario, Perera, A.H., D.L. Euler, and I.D. Thompson (eds.). UBC Press, Vancouver, BC.
  • Makarim, Nabiel, et al. BAPEDAL and CIDA-CEPI. 1998. Assessment of 1997 Land and Forest Fires in Indonesia: National Coordination. From "International Forest Fire News", #18, page 4-12, January 1998.
  • Martell, D.L. 1994. The impact of fire on timber supply in Ontario. For. Chron. 70:164-173.
  • Martell, D.L. 1996. Old-growth, disturbance, and ecosystem management: commentary. Can. J. Bot. 74:509-510.
  • Miyanishi, K., and E.A. Johnson. 2001. A re-examination of the effects of fire suppression in the boreal forest. Can. J. For. Res. 31:1462-1466.
  • Miyanishi, K., S.R.J. Bridge, AND E.A. Johnson. 2002. Wildfire regime in the boreal forest. Conserv. Biol. 16:1177-1178.
  • Pyne, S.J. et al. 1996. Introduction to Wildland Fire. Wiley, New York.
  • Stocks, B.J. 1991. The extent and impact of forest fires in northern circumpolar countries. P. 197-202 in Global biomass burning: atmospheric, climatic and biospheric implications, Levine, J.S. (ed.). MIT Press, Cambridge, MA.
  • Wang, P.K. 2003. The physical mechanism of injecting biomass burning materials into the stratosphere during fire-induced thunderstorms. American Geophysical Union fall meeting. Dec. 8-12. San Francisco.
  • Ward, P.C., and W. Mawdsley. 2000. Fire management in the boreal forests of Canada. P. 274-288 In Fire, climate change, and carbon cycling in the boreal forest, Kasischke, E.S., and B.J. Stocks (eds.). Springer, New York, NY.
  • Ward, P.C., and A.G. Tithecott. 1993. The impact of fire management on the boreal landscape of Ontario. Aviation, Flood and Fire Management Branch Publication No. 305. Ont. Min. Nat. Res., Queens Printer for Ontario, Toronto, ON.
  • Ward, P. C., Tithecott, A. G., & Wotton, B. M. 2001. Reply—a re-examination of the effects of fire suppression in the boreal forest. Canadian Journal of Forest Research, 31(8), 1467.
  • Weber, M.G., and B.J. Stocks. 1998. Forest fires in the boreal forests of Canada. P. 215-233 in Large forest fires, Moreno, J.M. (ed.). Backhuys Publishers, Leiden, The
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