A wildfire, also known as a wildland fire, forest fire, brush fire, vegetation fire, grass fire, peat fire, 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, slash-and-burn farming, arson, volcano eruption, pyroclastic cloud from active volcano, and underground coal fire. Heat waves, droughts, and cyclical climate changes such as El Niño can also dramatically increase 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".
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 generally accepted that wildfires are a natural part of the ecosystem of numerous wildlands, where some 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) as a way to eliminate competition from less fire tolerant species. Smoke, charred wood, and heat are common fire cues that stimulate the germination of seeds (Keeley and Fotheringham 1997). 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.
However, 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 (Keeley 1995, Zedler 1995). These weeds create a positive feedback loop, increasing fire frequency even more (Brooks, et al. 2004).
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 are often deliberately lit .
The evaporation of water in plants is balanced by water absorbed from the soil. When this balance is not maintained, plants dry out and when under this kind of stress they 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:
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.
Enlarge picture 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.
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 wild land, 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. 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 wild land/urban interface where communities connect with wild open space. Prescribed burns 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 often threatened directly by wildfire. Expanding 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.
Many states in the United States, Canadian provinces and many countries around the world =till 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.
|SOLUTIONS||SIZE AREA||RISK LEVEL||DETECTION WITHIN|
|Aero/satellite||Very large (>250,000 acres)||Low||30 acres (12 ha)|
|Infrared/smoke scanners||Medium (10,000-250,000 acres)||Medium||3 acres (2.4 ha)|
|Local sensor network||Small (<10,000 acres)||High||150 sq ft (15 sq m)|
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).
Although it is a relatively new approach, it seems to be the only solution able to penetrate thick vegetation and guarantee early detection without false alarms, as well as detecting crawling wildfires. The main limitation of this technology is its high cost which at this time limit its application to small areas.
These have a disadvantage in that they are "blind" to obstacles like thick vegetation, therefore they can miss crawling wildfires for a long time and have still frequent false alarms, but are the best approach to wider areas. Smoke and hot-air-column scanners have the advantage of "looking higher", making them able to locate a wildfire of any size, but do not perform well during strong wind (which is, ironically, the riskiest situation).
Many studies have been done in this field, some producing interesting results. Limitations include the long distance to satellites in geostationary orbits and the short window of observation time for satellites in polar orbits.
The vast majority of wildfires are suppressed before they grow out of control. For example, in 2004, US firefighters contained more than 99% of all new wildfires during initial action. That record was achieved despite the volatile conditions that prevailed in much of that year's USA fire season. However, the wildfires that escaped initial actions and grew above accounted for the bulk of acres burned, and nearly 75% of all suppression expenditures.
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.
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 wild land fire without the fire outflanking them. As a last resort, all wild land firefighters carry a fire shelter. In an 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.
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.
Wildfires can affect climate and weather and have major impacts on regional and global pollution (Bravo, et al., 2002)).
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 in 1997 is estimated to have released between 0.81 and 2.57 gigatonnes of Carbon Dioxide into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels.
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.
Wildland fire emissions contain greenhouse gasses and a number of criteria pollutants which can have a substantial impact on human health and welfare (Douglass 2008).
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.
Every year, the burnt surface represents about:
Canadian Forest Fire Management Agencies
Forest fire management is under provincial/territorial jurisdiction (with the exception of the Yukon Territory) with operational fire-control services and coordination of resource-sharing provided by the Canadian Interagency Forest Fire Centre. Parks Canada is responsible for forest fire management in our National Parks. Specific information on fire conditions can be obtained from the appropriate agency listed below. CIFFC is also is the principal source for the statistics used in preparing the weekly National Forest Fire Situation Report.
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