WikiPortallus: Wildfire.html

A wildfire is any uncontrolled, non-structure fire that occurs in the wildland.¹² Synonyms such as wildland fire, forest fire, brush fire, vegetation fire, grass fire, peat fire, bushfire (in Australasia), and hill fire are commonly used. Causes are numerous³⁴ and include lightning,⁵ human carelessness, slash-and-burn farming,⁶ arson,⁷ volcanic activity, pyroclastic clouds, and underground coal fires. Nine out of ten wildfires are reportedly caused by some human interaction.⁸ Heat waves, droughts, and cyclical climate changes such as El Niño can also dramatically increase the risk of wildfires.

Wildfires are common in various parts of the world, occurring in cycles. They are often considered beneficial to wildlands, as many plant species are depend on the effects of fire for growth and reproduction. However, large wildfires often have detrimental atmospheric consequences.

Prevention, detection, and suppression strategies have varied over the years, but now incorporate techniques that permit and even encourage fires in some regions. However, with extensive urbanization of wildlands, wildfires often involve the destruction of homes and other property located in the wildland urban interface, a zone of transition between developed areas and undeveloped wildland.

Wildfire was once a synonym for Greek fire as well as a word for any furious or destructive conflagration.⁹. 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".

Ecology

Wildfires are common in climates that are sufficiently moist to allow the growth of trees but feature extended dry, hot periods. Such places include the vegetated areas of Australia, 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 winds¹⁰ and periods of drought. Fire prevalence is also high during the summer and autumn months, when fallen branches, leaves, grasses, and scrub dry out and become more flammable.¹¹¹² Global warming may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires.¹³¹⁴¹⁵ Forest fires can have a dramatic effect on climate change, dramatically increasing carbon released into the atmosphere and ceasing vegetation growth, which inhibits carbon uptake.¹⁶

Wildfires are considered a natural part of the ecosystem of numerous wildlands,⁸¹¹ where some plants have evolved to survive fires by a variety of strategies, such as fire-resistant seeds and reserve shoots that sprout after a fire. Smoke, charred wood, and heat are common fire cues that stimulate the germination of seeds.¹⁷ Exposure to smoke from burning plants promotes germination in other types of plants by inducing the production of the orange butenolide.¹⁸ Plants of the genus eucalypts (e.g. eucalyptus) contain flammable oils¹⁹ that can encourage fire, thought to be a strategy to eliminate competition from less fire-tolerant species.^{citation needed}

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.²⁰²¹ Invading species such as Lygodium microphyllum and Bromus tectorum may create a positive feedback loop, increasing fire frequency even more.²²²³

Atmospheric effects

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.²⁴ 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 kilometres (3,100 mi). 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.²⁵ Wildland fire emissions contain greenhouse gases and a number of criteria pollutants which can have a substantial impact on human health and welfare.²⁶ Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigatonnes of CO₂ into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels.²⁷ Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15%.²⁸

Behavior

Fire behavior is often complex and variably dependent on factors such as fuel type, moisture content, windspeed, and topology,²⁹ but can be described as follows:⁸

Physical Properties

Fires start when a combustible material with an adequate supply of oxygen is subjected to enough heat and is able to sustain a chain reaction. This is commonly called the fire tetrahedron. No fire can exist without all of these elements being in place.⁴

The temperature at which a material may decompose, release flammable gases, and ignite is termed flash point (dry wood is about 300°C).⁴³⁰ Even before the actual flames arrive, fires can dry and pre-heat flammable material through convection and thermal radiation.⁸

A high moisture content usually prevents ignition and slows propagation,²⁹ because higher temperatures are required to evaporate the contained water and heat the material to its flash point.³¹ Less dense material such as grasses and leaves contain less water than denser material such as branches and trunks.⁸ Plants continuously lose water to evaporation, but water loss is usually balanced by water absorbed from the soil, humidity,³² or rain.³³ When this balance is not maintained, plants dry out and are therefore more flammable, often a consequence of a long, hot, dry periods.³³³⁴³⁵

Fuel Type

Wildfires and their spread vary greatly based on the flammable material present and its vertical arrangement. Fuel density is goverened by topography, as land shape determines factors such as available sunlight and water for plant growth. Fuels uphill from a fire are more readily dried and warmed than those downhill, yet burning logs can roll downhill. Overall, fuel types can be characterized as follows:⁸²⁹³⁴³⁶

Weather

Sunlight warms the ground during the day and causes air currents to travel uphill, and downhill during the night as the land cools. Wildfires and fanned by these winds and often follow the air currents over hills and through valleys.⁸ US 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.³⁸

Wildfires can move at tremendous speeds up to 14 miles per hour (23 km/h).⁴ Dense clouds of burning embers may push relentlessly ahead of the flames crossing firebreaks without pause. Wildfires may spread by jumping or spotting, as burning materials can jump over roads, rivers, or even firebreaks and start distant fires.⁵³³ In Australian bushfires, spot fires have been documented "up to 10 kilometres (6 mi) ahead of the fire front."³⁹

Wildfire Front

A fire's front is the portion sustaining continuous flaming combustion, where unburned material meets active flames. However, a front may also include the smouldering transition between unburned and burned material.³⁸

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.

Extremes

Air rises as it is heated, and large wildfires create powerful updrafts that will draw in new air from surrounding areas.⁸ These self-generated winds are often 10-times faster than ambient wind, encourage spotting, and severe gusts may cause the fire to spread into crown fuels.⁴^:3 Extreme fire behavior includes wide rates of spread, prolific crowning and/or spotting, the presence of fire whirls, or a strong convection column.³⁸

Prevention

Many wildland areas are now considered fire-dependent and previous policies of complete suppression are believed to have upset natural cycles.⁴¹^{:3, 37} Current wildfire prevention programs employ techniques such as wildland fire use and prescribed burns (controlled burns).¹² 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.⁴² These techniques allow supervising agencies to achieve specific objectives such as air quality management, ecology maintenance, and resource protection.²³ Controlled burns clear much of the undergrowth through forest and woodland areas, reducing fuel buildup and improving travel and hunting activities. Current policies often permit fires to burn to maintain their ecological role, so long as the risks of escape onto high-value areas are mitigated.⁴¹^:42

Additionally, underbrush and ladder fuels may be removed mechanically by hand crews.⁸ Chain saws and large equipment are used to thin out ladders fuels and shred trees and vegetation to a mulch. Such techniques are best used within the wildland/urban interface where communities connect with wild open space.

Building codes in fire-prone areas typically require that structures be built of flame-resistant materials⁴³ and firebreaks be maintained by clearing flammable materials within a prescribed distance from the edifice.⁴⁴ Additionally, residents may invest in their own firefighting equipment.

Detection

Fast and effective detection is a key factor in wildfire fighting. Recently, there have been significant efforts to create automatic solutions for early wildfire detection. An integrated approach is best, based on a practical combination of different detection systems depending on wildfire risk and the size of the area^{citation needed}.

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 for the long distance to satellites and desabiled in geostationary orbits and the short window of observation time for satellites in polar orbits.

Suppression

Complete fire suppression is no longer an expectation, but the majority of wildfires are extinguished before they grow out of control. While more than 99% of all new wildfires are contained and fire suppression does reduce the area burned, escaped wildfires can cause extensive damage.⁴⁵^:1560 In 2002, US suppression efforts cost 1.4 billion US dollars⁸^:1 ⁴⁶. Wildfires in the US during the year 2003 caused $2.3 billion US dollars in damage.⁴⁷ Yearly fires in Canada consume an average of 6,200,000 acres (25,000 km²)⁴⁸ and in the US an average of 7,320,000 acres (29,600 km²).⁴⁹

History

Wildland fire use as a concept had its origin when humans first gained the ability to suppress fires. Some fires were suppressed and others were allowed to burn based on human values and objectives. Native Americans and Euro-American settlers fought those fires that threatened their villages and settlements but left others to burn unabated. Even with the advent of a fire suppression capability in the late 1880s, control efforts were focused on areas of human development while fires in remote areas were largely ignored.

The fire exclusion policies of Canadian wildfire management agencies began around the 1900s, focusing on agressive attacks to limit areas burned by wildfires. Current efforts recognize fire as a natural component in wildland systems.⁴⁵^:1547

The policy of the United States Forest Service from 1905 to the 1960s was to control fires to less than 10 acres by 10 a.m. the following day (the 10 A.M. Policy).²³⁴¹^:35 This resulted in the buildup of fuel in some ecosystems such as dry ponderosa pine forests. 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. The passage of the 1964 Wilderness Act encouraged the allowance of natural processes to occur, including fire.⁴¹^:36 The U.S. Forest Service changed its policy in the 1970s from complete suppression to fire management.⁴¹^:37 ²³ While the Yellowstone fires of 1988 were caused by escaped fires from controlled burns, later investigations proved the fire use policy was appropriate, though needing strengthening and improvement.⁴¹^:36 After the 1994 US fire season which included the South Canyon Fire that killed 14 firefighters, a more comprehensive fire policy was created, recognizing the need for fire in the maintenance of wildland systems.⁸⁵⁰ However, as a result of missed fire cycles, there remains a excess of vegetation overgrowth from previous years of complete suppression.

Goals

Protection of human life (firefighters and civilians) is first priority, then other resources according to value, human health and safety, ecological, social and legal consequences, and the costs of protection.⁴¹^:27-28 ⁴⁶ In very severe, large fires, protection of life is sometimes the only possible action.

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.⁵¹

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.

Defendibility of private property is also considered, as more effort will be expended on saving a house with a tile roof than one with a wooden-shake roof.

Suppressing fires in publicly-owned forested areas is generally of least priority. 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.

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.

Tactics

Managing 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.

Most fire-prone areas have large firefighter services to help control wildfires. Typically, forest fire fighting organizations will use large crews of 20 or more people who travel in trucks to the fire.

Large fires often become extended campaigns and temporary fire camps are constructed to provide food, showers, and rest to fire crews. Smokejumpers and Hotshot crews are often used, consisting of highly-skilled firefighters specially trained in wildland fire suppression tactics. They are equipped to work in remote areas for extended periods of time with little logistical support.

Direct attack

Direct attack is any treatment applied directly to burning fuel such as wetting, smothering, or chemically quenching the fire or by physically separating the burning from unburned fuel. This includes the work of fire engines, fire crews, and aircraft applying water or some fire retardant directly to the burning fuel.

Other personnel are organized into fast attack teams typically consisting of 5–8 personnel. These fast attack teams are helicoptered into smaller fires or hard to reach areas as a preemptive strike force. 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, smokejumpers may parachute into site from fixed-wing aircraft. They use portable pumps to douse small fires and chainsaws to construct firebreaks or helicopter landing pads if more resources are required.

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.

Control lines

Attempts to control wildfires may also include by controlling the area that it can spread to by creating control lines: boundaries that contain no combustible material.

Control lines may consist of physically removing combustible material with tools and equipment such shovels, rakes, pulaskis, and bulldozers. Lines may also be created by backfiring: creating small, low-intensity fires using driptorches, or flares. The resultant fires are 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).

Fires on the wildland/urban interface

In addition to excessive fuel accumulation from years of complete suppression, expansive urbanization is a primary reason for the catastrophic losses experienced in recent wildfires. The population growth in these fringe areas also discourages the use of current fuel management techniques. Smoke is an irritant. Attempts to thin out the fuel load is met with opposition due to desirability of forested areas and natural habitats. Additionally, federal policies that cover the wildland areas usually differs from local and state policies that govern urban lands.²³^:14 ⁴¹^:38-40 However, fuel buildup can result in costly, devastating fires as more new houses and ranches are built adjacent to wilderness areas. Communities such as Sydney and Melbourne in Austrailia have literally built themselves in the middle of highly flammable forests. The city of Cape Town, South Africa lies on the fringe of the Table Mountain National Park.

Continued growth in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism.⁵¹

The ecological benefits of fire is often superceded by the economic benefits of protecting structures and lives.⁴⁷

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).

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.

Many states in the United States, Canadian provinces and many countries around the world 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^{citation needed}.

Statistics

Notable wildfires

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