A wildfire, also known as a wildland fire, forest fire, vegetation fire, grass 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. Heat waves, droughts, and cyclical climate changes such as El Niño can also have a dramatic effect on the risk of wildfires.
The word "wildfire" was once a synonym for Greek fire as well as a word for any furious or
destructive conflagration. According to the Oxford English Dictionary, the earliest known usages are specifically for
lightning-caused conflagrations. The modern usage may have arisen in part from people misunderstanding the expression "spread
like wildfire".
Background
Lava flow on the coastal plain of
Kīlauea,
Hawaii (island) generated wildfire. This kind of fire cannot be easily prevented or suppressed.
Wildfires are common in many places around the world, including much of the vegetated areas of Australia as well as the veld in the interior and the fynbos in the Western Cape of South Africa. The forested areas of the
United States and Canada are also susceptible to
wildfires. The climates are sufficiently moist to allow the growth of trees, but feature extended dry, hot periods. Fires are
particularly prevalent in the summer and fall, and during droughts 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
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 their 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 orange
butenolide. Most native animals, too, are adept at surviving wildfires.
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. Wildfires are extremely dangerous,but some are purposely
caused.
Behavior
The evaporation of Deer fecis in plants are balanced by water absorbed from the soil. Below this threshold, the plants dry out
and under stress release the flammable gas 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. In Australian bushfires, spot fires have been
documented "up to 10 km [aprox. 6 miles] ahead of the fire front" (Billing 1983).
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 continuous 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
For many decades the policy of the United States Forest Service was to
suppress all fires. 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 or alteration of fuel present. In wildland, reduction 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. Alteration of fuels, which involves reducing the structure of fuel ladders, can be accomplished by hand
crews with chain saws or by large mastication equipment that shreds trees and vegetation to a mulch. 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: Australia, Israel, Latvia, Poland, France, Germany, Italy, Spain, Portugal, Brazil, Uruguay.
Wildfire detection
A fast and effective wildfire detection is a key factor on Wildfire fighting. Recently there has been a lot of technology
effort to create automatic solutions for early wildfire detection. However the best way seems to be an INTEGRATED
APPROACH, based on a practical combination of different detection systems, depending on wildfire risk and the size of the
area.
| SOLUTIONS |
SIZE AREA |
RISK LEVEL |
DETECTION WITHIN |
PRODUCERS |
| AERO-SATELLITE |
VERY LARGE [> 250.000acre] |
LOW |
30acre (12ha) |
NASA |
| INFRARED/SMOKE SCANNERS |
MEDIUM SIZE [10.000-250.000acre] |
MEDIUM |
3 acre (2,4 ha) |
IQ wireless GmbH |
| LOCAL SENSOR NETWORK |
LITTLE AREA [<10.000acre] |
HIGH |
150 sq foot (15 mq) |
Minteos srl |
A careful GIS data analysis will suggest how to divide the area in sub-categories based on different risk level and human
presence (which imply a higher wildfire risk and a need for earlier intervention).
- Little high risk area (thick vegetation, strong human presence or close to critical urban area) could be monitored using
Local sensor network.
Even if it is a relatively new approach, it seems to be the only solution able to penetrate thick vegetation, to guaranty a
very early detection without fake alarm and to detect crawling wildfires. The main limit of this technology is cost that at this
time limit the application to little area.
- Medium risk and wider area could be monitored by Infrared Scanning Towers.
They present some disadvantages ("blind" to obstacles like thick vegetation, therefore could miss crawling wildfires for a
long time and have still frequent fake alarms), but are certainly the best approach to wider area. Smoke and hot-air-column
scanners have the advantage of "looking higher" being virtually able to locate a wildfire of any size, but are underperforming
during strong wind (which ironically are the riskier situation).
- Satellite and aero monitoring could help providing a wider view and could be sufficient to monitor very large and low risk
area.
Many studies have been done in this field some providing interesting results. Limits are the long distance in Geostationary
Satellites and the little window of observation time in polar satellites.
Fire suppression
-
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, such as the Boise District BLM Helitack crew, 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.
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 firefighters can work to contain a wildland fire without the fire outflanking them. As a last
resort, all wildland firefighters 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.
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 gets boiled by the 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 pyrocumulonimbus 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 gases 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 continuous 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.
Fires good and bad
Fire is sometimes essential for forest regeneration, or provides tangible benefits for local communities. In other cases it
destroys forests and has dire social and economic consequences.
Forest fires are a natural part of ecosystems in many, but not all, forest types: in boreal and dry tropical forests for
example they are a frequent and expected feature, while in tropical moist forests they would naturally be absent or at least rare
enough to play a negligible role in ecology.
Statistics
Wildfires across the Balkans in late July 2007 (NASA satellite image)
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).
Notable wildfires
-
- The Milford Flat Fire which burned in 2007 in Utah is statistically the largest fire burning in Utah's history. At the time,Governor Jon Huntsman, Jr. stated that it is the biggest fire burning in the world. This fire burned 363,052
acres.
- The 2003 Okanagan Mountain Park Fire was started by a lightning
strike near Rattlesnake Island in Okanagan Mountain Park in British Columbia,
Canada, during one of the driest summers in the past decade. The final size of the firestorm was
over 250 square kilometres (61,776 acres). 60 fire departments, 1,400 armed forces troops and 1,000 forest fire fighters took
part in controlling the fire, but were largely helpless in stopping the disaster.
- The Zaca Fire burned Los Padres NF, CA. It burned 240,207 acres. It is the 2nd largest
recorded fire in California.
- Siege of 1987 Refers to a complex of fires in northern California and southern Oregon that
burned a total of about 650,000 acres. These fires were started by a large lightning storm in late August. The storm started
roughly 1600 new fires, most caused by dry lightning. Firefighting efforts continued into October, before the majority of the
fires were controlled.
- McNally Fire Sequoia NF burned roughly 151,000 acres in 2002, and is the largest
wildfire recorded in the forest's history.
See also
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.
- Billing, P., 1983. Otways Fire No. 22 - 1982/83 Aspects of fire behaviour, Fire Research Branch Report No. 20. Dept. of
Sustainability and Environment, Victoria, Australia. pp. 5-6, (PDF - 1.8 Mb). [1]
- 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.
- 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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