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 al
so 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.
so 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 plant
s 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.
s 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).
"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 wildfi
re 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.
re 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.
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 chapa
rral. 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.
rral. 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. A wildfireThe 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.
FIRE SUPRESSION
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 f
ast 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.
ast 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).
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
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.
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 Yellowstone National Park Fire of 1988 burned well over 793,880 acres (321,271 ha) before the winter snows put out the flames. (See: Yellowstone fires of 1988)
- 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.
- The 2003 Canberra bushfires infinged on the Australian capital itself. A firestorm raced through Canberra suburbs on January 18 2003 and damaged or destroyed 431 homes.
- The 2007 Greek fires were some of the deadliest in world history, killing at least 64 people in Peloponnese and Evia
Source:http://encyclopedia.thefreedictionary.com/Forest+Fires
No comments:
Post a Comment