Wildfire

A wildfire, wildland fire or rural fire is an uncontrolled in an area of combustible  occurring in s. Depending on the type of vegetation present, a wildfire can also be classified more specifically as a brush fire,  (in Australia), desert fire, forest fire, grass fire, hill fire, peat fire, vegetation fire, or veld fire. Many organizations consider wildfire to mean an unplanned and unwanted fire, while wildland fire is a broader term that includes prescribed fire as well as wildland fire use (WFU; these are also called monitored response fires).

indicates that wildfires began soon after the appearance of terrestrial plants 420 million years ago. Wildfire's occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna. Earth is an intrinsically flammable planet owing to its cover of carbon-rich vegetation, seasonally dry climates, atmospheric oxygen, and widespread lightning and volcanic ignitions.

Wildfires can be characterized in terms of the cause of ignition, their physical properties, the combustible material present, and the effect of weather on the fire. Wildfires can cause damage to property and human life, although naturally occurring wildfires may have beneficial effects on native vegetation, animals, and ecosystems that have evolved with fire.

High-severity wildfire creates habitat (also called "snag forest habitat"), which often has higher species richness and diversity than unburned old forest. Many plant species depend on the effects of fire for growth and reproduction. Wildfires in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have strongly negative ecological effects.

Wildfire behavior and severity result from a combination of factors such as available fuels, physical setting, and weather. Analyses of historical meteorological data and national fire records in western North America show the primacy of climate in driving large regional fires via wet periods that create substantial fuels, or drought and warming that extend conducive fire weather.

Strategies for wildfire prevention, detection, control and suppression have varied over the years. One common and inexpensive technique is ing: intentionally igniting smaller fires to minimize the amount of flammable material available for a potential wildfire. Vegetation may be burned periodically to maintain high species diversity and limit the accumulation of plants and other debris that may serve as fuel. Wildland fire use is the cheapest and most ecologically appropriate policy for many forests. Fuels may also be removed by logging, but such thinning treatments may not be effective at reducing fire severity under extreme weather conditions. Wildfire itself is reportedly "the most effective treatment for reducing a fire's rate of spread, fireline intensity, flame length, and heat per unit of area", according to Jan Van Wagtendonk, a biologist at the Yellowstone Field Station. Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a be maintained by clearing flammable materials within a prescribed distance from the structure.

Causes
Three major natural causes of wildfire ignitions exist:

The most common direct human causes of wildfire ignition include, discarded cigarettes, power-lines (as detected by ), and sparks from equipment. Ignition of wildland fires via contact with hot rifle-bullet fragments is also possible under the right conditions. Wildfires can also be started in communities experiencing, where land is cleared quickly and farmed until the soil loses fertility, and clearing. Forested areas cleared by logging encourage the dominance of flammable grasses, and abandoned overgrown by vegetation may act as fire corridors. Annual grassland fires in southern stem in part from the destruction of forested areas by  herbicides, explosives, and mechanical land-clearing and -burning operations during the.

The most common cause of wildfires varies throughout the world. In Canada and northwest China, lightning operates as the major source of ignition. In other parts of the world, human involvement is a major contributor. In Africa, Central America, Fiji, Mexico, New Zealand, South America, and Southeast Asia, wildfires can be attributed to human activities such as agriculture,, and land-conversion burning. In China and in the, human carelessness is a major cause of wildfires. In the United States and Australia, the source of wildfires can be traced both to lightning strikes and to human activities (such as machinery sparks, cast-away cigarette butts, or ). s burn in the thousands around the world, such as those in, New South Wales; , Pennsylvania; and several. They can also flare up unexpectedly and ignite nearby flammable material.

Spread
The spread of wildfires varies based on the flammable material present, its vertical arrangement and moisture content, and weather conditions. Fuel arrangement and density is governed in part by, as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be generally characterized by their fuels as follows:
 * Ground fires are fed by subterranean roots, and other buried . This fuel type is especially susceptible to ignition due to spotting. Ground fires typically burn by smoldering, and can burn slowly for days to months, such as  in  and Eastern, , which resulted from a  that unintentionally drained and dried the peat.
 * Crawling or surface fires are fueled by low-lying vegetation on the such as leaf and timber litter, debris, grass, and low-lying shrubbery. This kind of fire often burns at a relatively lower temperature than crown fires (less than 400 C) and may spread at slow rate, though steep slopes and wind can accelerate the rate of spread.
 * Ladder fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and s., , and other s that scale trees may also encourage ladder fires.
 * Crown, canopy, or aerial fires burn suspended material at the canopy level, such as tall trees, vines, and mosses. The ignition of a crown fire, termed crowning, is dependent on the density of the suspended material, canopy height, canopy continuity, sufficient surface and ladder fires, vegetation moisture content, and weather conditions during the blaze. Stand-replacing fires lit by humans can spread into the, damaging ecosystems not particularly suited for heat or arid conditions.
 * In monsoonal areas of north Australia, surface fire spread, including across intended firebreaks, by burning or smoldering pieces of wood or burning tufts of grass carried intentionally by large flying birds accustomed to catch prey flushed out by wildfires. Species implicated are Black Kite ('), Whistling Kite ('), and Brown Falcon (). Local s have known of this behavior for a long time, including in their.

Physical properties
Wildfires occur when all the necessary elements of a fire triforce come together in a susceptible area: an ignition source is brought into contact with a combustible material such as, that is subjected to enough heat and has an adequate supply of oxygen from the ambient air. A high moisture content usually prevents ignition and slows propagation, because higher temperatures are needed to evaporate any water in the material and heat the material to its. Dense forests usually provide more shade, resulting in lower ambient temperatures and greater, and are therefore less susceptible to wildfires. Less dense material such as grasses and leaves are easier to ignite because they contain less water than denser material such as branches and trunks. Plants continuously lose water by, but water loss is usually balanced by water absorbed from the soil, humidity, or rain. When this balance is not maintained, plants dry out and are therefore more flammable, often a consequence of droughts.

A wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the ing transition between unburned and burned material. As the front approaches, the fire heats both the surrounding air and woody material through and. First, wood is dried as water is vaporized at a temperature of 100 C. Next, the of wood at 230 C releases flammable gases. Finally, wood can smoulder at 380 C or, when heated sufficiently, ignite at 590 C. Even before the flames of a wildfire arrive at a particular location, from the wildfire front warms the air to 800 C, which pre-heats and dries flammable materials, causing materials to ignite faster and allowing the fire to spread faster. High-temperature and long-duration surface wildfires may encourage or torching: the drying of  and their subsequent ignition from below.

Wildfires have a rapid forward rate of spread (FROS) when burning through dense uninterrupted fuels. They can move as fast as 10.8 km/h in forests and 22 km/h in grasslands. Wildfires can advance tangential to the main front to form a flanking front, or burn in the opposite direction of the main front by backing. They may also spread by jumping or spotting as winds and vertical columns carry firebrands (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as s. Torching and fires in tree canopies encourage spotting, and dry ground fuels around a wildfire are especially vulnerable to ignition from firebrands. Spotting can create spot fires as hot embers and firebrands ignite fuels downwind from the fire. In Australian bushfires, spot fires are known to occur as far as 20 km from the fire front.

The incidence of large, uncontained wildfires in has increased in recent years, significantly impacting both  and agriculturally-focused areas. The physical damage and health pressures left in the wake of uncontrolled fires has especially devastated farm and operators in affected areas, prompting concern from the community of  providers and advocates servicing this specialized occupational population.

Especially large wildfires may affect air currents in their immediate vicinities by the : air rises as it is heated, and large wildfires create powerful s that will new, cooler air from surrounding areas in s. Great vertical differences in temperature and humidity encourage s, strong winds, and s with the force of tornadoes at speeds of more than 80 km/h. Rapid rates of spread, prolific crowning or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions.

The thermal heat from wildfire can cause significant of rocks and boulders, heat can rapidly expand a boulder and  can occur, which may cause an object's structure to fail.

Effect of climate
s, s, such as, and regional weather patterns such as high-pressure ridges can increase the risk and alter the behavior of wildfires dramatically. Years of precipitation followed by warm periods can encourage more widespread fires and longer fire seasons. Since the mid-1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season, or the most fire-prone time of the year, in the. may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires. A 2015 study indicates that the increase in may be attributable to. A study of  deposits going back over 8,000 years found warmer climate periods experienced severe droughts and stand-replacing fires and concluded climate was such a powerful influence on wildfire that trying to recreate presettlement forest structure is likely impossible in a warmer future.

Intensity also increases during daytime hours. Burn rates of smoldering logs are up to five times greater during the day due to lower humidity, increased temperatures, and increased wind speeds. Sunlight warms the ground during the day which creates air currents that travel uphill. At night the land cools, creating air currents that travel downhill. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys. Fires in Europe occur frequently during the hours of 12:00 p.m. and 2:00 p.m. Wildfire suppression operations in the United States revolve around a 24-hour fire day that begins at 10:00 a.m. due to the predictable increase in intensity resulting from the daytime warmth.

In 2019 extreme heat and dryness caused massive wildfires in, , , , and in the. The fires in the latter were caused mainly by illegal logging. The smoke from the fires expanded on huge territory including major cities, dramatically reducing air quality.

Ecology
Wildfire's occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna. Wildfires are common in climates that are sufficiently moist to allow the growth of vegetation but feature extended dry, hot periods. Such places include the vegetated areas of Australia and, the in southern Africa, the  in the Western Cape of South Africa, the forested areas of the United States and Canada, and the.

High-severity wildfire creates habitat (also called “snag forest habitat”), which often has higher species richness and diversity than unburned old forest. Plant and animal species in most types of North American forests evolved with fire, and many of these species depend on wildfires, and particularly high-severity fires, to reproduce and grow. Fire helps to return nutrients from plant matter back to soil, the heat from fire is necessary to the germination of certain types of seeds, and the snags (dead trees) and early successional forests created by high-severity fire create habitat conditions that are beneficial to wildlife. Early successional forests created by high-severity fire support some of the highest levels of native biodiversity found in temperate conifer forests. Post-fire logging has no ecological benefits and many negative impacts; the same is often true for post-fire seeding.

Although some ecosystems rely on naturally occurring fires to regulate growth, some ecosystems suffer from too much fire, such as the in  and lower-elevation deserts in the American Southwest. The increased fire frequency in these ordinarily fire-dependent areas has upset natural cycles, damaged native plant communities, and encouraged the growth of non-native weeds. , such as ' and ', can grow rapidly in areas that were damaged by fires. Because they are highly flammable, they can increase the future risk of fire, creating a that increases fire frequency and further alters native vegetation communities.

In the, drought, logging, cattle ranching practices, and agriculture damage fire-resistant forests and promote the growth of flammable brush, creating a cycle that encourages more burning. Fires in the rainforest threaten its collection of diverse species and produce large amounts of CO2. Also, fires in the rainforest, along with drought and human involvement, could damage or destroy more than half of the Amazon rainforest by the year 2030. Wildfires generate ash, reduce the availability of organic nutrients, and cause an increase in water runoff, eroding away other nutrients and creating conditions. A 2003 wildfire in the burned off 2.5 km2 of  and the underlying  layers. Afterwards, wind erosion stripped the ash and the exposed soil, revealing archaeological remains dating back to 10,000 BC. Wildfires can also have an effect on climate change, increasing the amount of carbon released into the atmosphere and inhibiting vegetation growth, which affects overall carbon uptake by plants.

In there is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals, (FRIs) that typically vary from 150 to 200 years with dryer lowland areas burning more frequently than wetter upland areas.

Plant adaptation
Plants in wildfire-prone often survive through adaptations to their local. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate. For example, plants of the genus  contain flammable oils that encourage fire and hard leaves to resist heat and drought, ensuring their dominance over less fire-tolerant species. Dense bark, shedding lower branches, and high water content in external structures may also protect trees from rising temperatures. Fire-resistant seeds and reserve s that sprout after a fire encourage species preservation, as embodied by. Smoke, charred wood, and heat can stimulate the germination of seeds in a process called . Exposure to smoke from burning plants promotes in other types of plants by inducing the production of the orange.

Grasslands in Western, Malaysian forests, and Indonesian  forests are believed to have resulted from previous periods of fire. deadwood litter is low in water content and flammable, and the shrub quickly sprouts after a fire. Cape lilies lie dormant until flames brush away the covering and then blossom almost overnight. rely on periodic fires to reduce competition, release seeds from their s, and clear the soil and canopy for new growth. in have adapted to and rely on low-intensity, surface fires for survival and growth. An optimum fire frequency for growth is every 3 to 10 years. Too frequent fires favor s, and infrequent fires favor species typical of.

Atmospheric effects
Most of the Earth's weather and air pollution resides in the, the part of the atmosphere that extends from the surface of the planet to a height of about 10 km. The vertical lift of a severe thunderstorm or can be enhanced in the area of a large wildfire, which can propel smoke, soot, and other  as high as the lower. Previously, prevailing scientific theory held that most particles in the stratosphere came from es, but smoke and other wildfire emissions have been detected from the lower stratosphere. Pyrocumulus clouds can reach 6100 m over wildfires. Satellite observation of smoke plumes from wildfires revealed that the plumes could be traced intact for distances exceeding 1600 km. Computer-aided models such as may help predict the size and direction of wildfire-generated smoke plumes by using.

Wildfires can affect local atmospheric pollution, and release carbon in the form of carbon dioxide. contain fine particulate matter which can cause cardiovascular and respiratory problems. Increased fire byproducts in the troposphere can increase ozone concentration beyond safe levels. Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigas (0.89 and 2.83 billion s) of CO2 into the atmosphere, which is between 13%–40% of the annual global carbon dioxide emissions from burning fossil fuels. Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming during winter months by as much as 15%. The Amazon is estimated to hold around 90 billion tons of carbon. As of 2019, earth's atmosphere has 415 parts per million of carbon, and the destruction of the Amazon would add about 38 parts per million.

History
In the, the first evidence of wildfire is plant fossils preserved as , dating to the  period (about ). Smoldering surface fires started to occur sometime before the Early period. Low atmospheric oxygen during the Middle and Late Devonian was accompanied by a decrease in charcoal abundance. Additional charcoal evidence suggests that fires continued through the period. Later, the overall increase of atmospheric oxygen from 13% in the Late Devonian to 30–31% by the was accompanied by a more widespread distribution of wildfires. Later, a decrease in wildfire-related charcoal deposits from the late Permian to the periods is explained by a decrease in oxygen levels.

Wildfires during the Paleozoic and Mesozoic periods followed patterns similar to fires that occur in modern times. Surface fires driven by dry seasons are evident in Devonian and Carboniferous forests. forests dating to the Carboniferous period have charred peaks, evidence of crown fires. In Jurassic forests, there is evidence of high frequency, light surface fires. The increase of fire activity in the late is possibly due to the increase of -type grasses. As these grasses shifted to more s, their high flammability increased fire frequency, promoting grasslands over woodlands. However, fire-prone habitats may have contributed to the prominence of trees such as those of the genera ', Pinus and ', which have thick bark to withstand fires and employ.

Human involvement
The human use of fire for agricultural and hunting purposes during the and  ages altered the preexisting landscapes and fire regimes. Woodlands were gradually replaced by smaller vegetation that facilitated travel, hunting, seed-gathering and planting. In recorded human history, minor allusions to wildfires were mentioned in the and by classical writers such as. However, while ancient Hebrew, Greek, and Roman writers were aware of fires, they were not very interested in the uncultivated lands where wildfires occurred. Wildfires were used in battles throughout human history as. From the, accounts were written of as well as customs and laws that governed the use of fire. In Germany, regular burning was documented in 1290 in the and in 1344 in the. In the 14th century, firebreaks were used for wildfire protection. In Spain during the 1550s, was discouraged in certain provinces by  due to the harmful effects of fires used in. As early as the 17th century, Native Americans were observed for many purposes including cultivation,, and warfare. Scottish botanist noted the native use of fire for tobacco cultivation, to encourage deer into smaller areas for hunting purposes, and to improve foraging for honey and grasshoppers. Charcoal found in sedimentary deposits off the Pacific coast of Central America suggests that more burning occurred in the 50 years before the than after the colonization. In the post-World War II, socio-economic changes led more stringent air quality standards and bans on fires that eliminated traditional burning practices. In the mid-19th century, explorers from HMS Beagle observed using fire for ground clearing, hunting, and regeneration of plant food in a method later named. Such careful use of fire has been employed for centuries in the lands protected by to encourage biodiversity.

Wildfires typically occurred during periods of increased temperature and drought. An increase in fire-related in s of northeastern  was linked to the period between AD 1050 and 1200, coinciding with the. However, human influence caused an increase in fire frequency. fire scar data and charcoal layer data in suggests that, while many fires occurred during severe drought conditions, an increase in the number of fires during 850 BC and 1660 AD can be attributed to human influence. Charcoal evidence from the Americas suggested a general decrease in wildfires between 1 AD and 1750 compared to previous years. However, a period of increased fire frequency between 1750 and 1870 was suggested by charcoal data from North America and Asia, attributed to human population growth and influences such as land clearing practices. This period was followed by an overall decrease in burning in the 20th century, linked to the expansion of agriculture, increased livestock grazing, and fire prevention efforts. A meta-analysis found that 17 times more land burned annually in California before 1800 compared to recent decades (1,800,000 hectares/year compared to 102,000 hectares/year).

According to a paper published in, the number of natural and human-caused fires decreased by 24.3% between 1998 and 2015. Researchers explain this a transition from to settled lifestyle and intensification of  that lead to a drop in the use of fire for land clearing.

Increases of certain native tree species (i.e. ) in favor of others (i.e. leaf trees) also increases wildfire risk, especially if these trees are also planted in s

Some, moved in by humans (i.e., for the ) have in some cases also increased the intensity of wildfires. Examples include species such as in California and  in Australia.

Prevention
Wildfire prevention refers to the preemptive methods aimed at reducing the risk of fires as well as lessening its severity and spread. Prevention techniques aim to manage air quality, maintain ecological balances, protect resources, and to affect future fires. North American firefighting policies permit naturally caused fires to burn to maintain their ecological role, so long as the risks of escape into high-value areas are mitigated. However, prevention policies must consider the role that humans play in wildfires, since, for example, 95% of forest fires in Europe are related to human involvement. Sources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture such as the slash-and-burn farming in Southeast Asia.

In 1937, U.S. President initiated a nationwide fire prevention campaign, highlighting the role of human carelessness in forest fires. Later posters of the program featured, characters from the Disney movie , and the official mascot of the ,. Reducing human-caused ignitions may be the most effective means of reducing unwanted wildfire. Alteration of fuels is commonly undertaken when attempting to affect future fire risk and behavior. Wildfire prevention programs around the world may employ techniques such as wildland fire use and prescribed or s. 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.

Vegetation may be burned periodically to maintain high species diversity and frequent burning of surface fuels limits fuel accumulation. Wildland fire use is the cheapest and most ecologically appropriate policy for many forests. Fuels may also be removed by logging, but fuels treatments and thinning have no effect on severe fire behavior Wildfire models are often used to predict and compare the benefits of different fuel treatments on future wildfire spread, but their accuracy is low.

Wildfire itself is reportedly "the most effective treatment for reducing a fire's rate of spread, fireline intensity, flame length, and heat per unit of area" according to Jan van Wagtendonk, a biologist at the Yellowstone Field Station.

Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a be maintained by clearing flammable materials within a prescribed distance from the structure. Communities in the also maintain s 5 to 10 m wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather. Continued residential development in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism. The ecological benefits of fire are often overridden by the economic and safety benefits of protecting structures and human life.

Detection
Fast and effective detection is a key factor in wildfire fighting. Early detection efforts were focused on early response, accurate results in both daytime and nighttime, and the ability to prioritize fire danger. s were used in the United States in the early 20th century and fires were reported using telephones, s, and s. Aerial and land photography using s were used in the 1950s until was developed for fire detection in the 1960s. However, information analysis and delivery was often delayed by limitations in communication technology. Early satellite-derived fire analyses were hand-drawn on maps at a remote site and sent via overnight mail to the. During the, a data station was established in , permitting the delivery of satellite-based fire information in approximately four hours.

Currently, public hotlines, s in towers, and ground and aerial patrols can be used as a means of early detection of forest fires. However, accurate human observation may be limited by, time of day, time of year, and geographic location. Electronic systems have gained popularity in recent years as a possible resolution to human operator error. A government report on a recent trial of three automated camera fire detection systems in Australia did, however, conclude "...detection by the camera systems was slower and less reliable than by a trained human observer". These systems may be semi- or fully automated and employ systems based on the risk area and degree of human presence, as suggested by data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via (GPS) into a collective whole for near-realtime use by wireless.

A small, high risk area that features thick vegetation, a strong human presence, or is close to a critical urban area can be monitored using a local. Detection systems may include s that act as automated weather systems: detecting temperature, humidity, and smoke. These may be battery-powered, solar-powered, or tree-rechargeable: able to recharge their battery systems using the small electrical currents in plant material. Larger, medium-risk areas can be monitored by scanning towers that incorporate fixed cameras and sensors to detect smoke or additional factors such as the infrared signature of carbon dioxide produced by fires. Additional capabilities such as, brightness detection, and color change detection may also be incorporated into sensor arrays.

Satellite and aerial monitoring through the use of planes, helicopter, or UAVs can provide a wider view and may be sufficient to monitor very large, low risk areas. These more sophisticated systems employ GPS and aircraft-mounted infrared or high-resolution visible cameras to identify and target wildfires. Satellite-mounted sensors such as 's and 's Along-Track Scanning Radiometer can measure infrared radiation emitted by fires, identifying hot spots greater than 39 C. The 's  combines remote-sensing data from satellite sources such as  (GOES),  (MODIS), and  (AVHRR) for detection of fire and smoke plume locations. However, satellite detection is prone to offset errors, anywhere from 2 to 3 km for MODIS and AVHRR data and up to 12 km for GOES data. Satellites in geostationary orbits may become disabled, and satellites in polar orbits are often limited by their short window of observation time. Cloud cover and image resolution may also limit the effectiveness of satellite imagery.

In 2015 a new fire detection tool is in operation at the (USDA)  (USFS) which uses data from the  (NPP) satellite to detect smaller fires in more detail than previous space-based products. The high-resolution data is used with a computer model to predict how a fire will change direction based on weather and land conditions. The active fire detection product using data from Suomi NPP's (VIIRS) increases the resolution of fire observations to 1,230 feet (375 meters). Previous NASA satellite data products available since the early 2000s observed fires at 3,280 foot (1 kilometer) resolution. The data is one of the intelligence tools used by the USFS and Department of Interior agencies across the United States to guide resource allocation and strategic fire management decisions. The enhanced VIIRS fire product enables detection every 12 hours or less of much smaller fires and provides more detail and consistent tracking of fire lines during long duration wildfires – capabilities critical for early warning systems and support of routine mapping of fire progression. Active fire locations are available to users within minutes from the satellite overpass through data processing facilities at the USFS Remote Sensing Applications Center, which uses technologies developed by the NASA Goddard Space Flight Center Direct Readout Laboratory in Greenbelt, Maryland. The model uses data on weather conditions and the land surrounding an active fire to predict 12–18 hours in advance whether a blaze will shift direction. The state of Colorado decided to incorporate the weather-fire model in its firefighting efforts beginning with the 2016 fire season.

In 2014, an international campaign was organized in South Africa's Kruger National Park to validate fire detection products including the new VIIRS active fire data. In advance of that campaign, the Meraka Institute of the Council for Scientific and Industrial Research in Pretoria, South Africa, an early adopter of the VIIRS 375m fire product, put it to use during several large wildfires in Kruger.

The demand for timely, high-quality fire information has increased in recent years. Wildfires in the United States burn an average of 7 million acres of land each year. For the last 10 years, the USFS and Department of Interior have spent a combined average of about $2–4 billion annually on wildfire suppression.

Suppression
Wildfire suppression depends on the technologies available in the area in which the wildfire occurs. In less developed nations the techniques used can be as simple as throwing sand or beating the fire with sticks or palm fronds. In more advanced nations, the suppression methods vary due to increased technological capacity. can be used to encourage snow fall, while s and water can be dropped onto fires by s,, and. Complete fire suppression is no longer an expectation, but the majority of wildfires are often extinguished before they grow out of control. While more than 99% of the 10,000 new wildfires each year are contained, escaped wildfires under extreme weather conditions are difficult to suppress without a change in the weather. Wildfires in Canada and the US burn an average of 54500 km2 per year.

Above all, fighting wildfires can become deadly. A wildfire's burning front may also change direction unexpectedly and jump across fire breaks. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire, which can make fires particularly dangerous. For example, during the 1949 in, USA, thirteen s died when they lost their communication links, became disoriented, and were overtaken by the fire. In the Australian, at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.

Costs of wildfire suppression
In California, the U.S. Forest Service spends about $200 million per year to suppress 98% of wildfires and up to $1 billion to suppress the other 2% of fires that escape initial attack and become large.

Wildland firefighting safety
Wildland fire fighters face several life-threatening hazards including, , and , as well as the risk of other injuries such as s,  and , , and even. Between 2000–2016, more than 350 wildland firefighters died on-duty.

Especially in hot weather condition, fires present the risk of heat stress, which can entail feeling heat, fatigue, weakness, vertigo, headache, or nausea. Heat stress can progress into heat strain, which entails physiological changes such as increased heart rate and core body temperature. This can lead to heat-related illnesses, such as heat rash, cramps, exhaustion or. Various factors can contribute to the risks posed by heat stress, including strenuous work, personal risk factors such as age and, dehydration, sleep deprivation, and burdensome. Rest, cool water, and occasional breaks are crucial to mitigating the effects of heat stress.

Smoke, ash, and debris can also pose serious respiratory hazards to wildland fire fighters. The smoke and dust from wildfires can contain gases such as, and , as well as  such as  and. To reduce smoke exposure, wildfire fighting crews should, whenever possible, rotate firefighters through areas of heavy smoke, avoid downwind firefighting, use equipment rather than people in holding areas, and minimize mop-up. Camps and command posts should also be located upwind of wildfires. Protective clothing and equipment can also help minimize exposure to smoke and ash.

Firefighters are also at risk of cardiac events including strokes and heart attacks. Fire fighters should maintain good physical fitness. Fitness programs, medical screening and examination programs which include stress tests can minimize the risks of firefighting cardiac problems. Other injury hazards wildland fire fighters face include slips, trips and falls, burns, scrapes and cuts from tools and equipment, being struck by trees, vehicles, or other objects, plant hazards such as thorns and poison ivy, snake and animal bites, vehicle crashes, electrocution from power lines or lightning storms, and unstable building structures.

Firefighter safety zone guidelines
The U.S. Forest Service publishes guidelines for the minimum distance a firefighter should be from a flame.

Fire retardant
Fire retardants are used to slow wildfires by inhibiting combustion. They are aqueous solutions of ammonium phosphates and ammonium sulfates, as well as thickening agents. The decision to apply retardant depends on the magnitude, location and intensity of the wildfire. In certain instances, fire retardant may also be applied as a precautionary fire defense measure.

Typical fire retardants contain the same agents as fertilizers. Fire retardant may also affect water quality through leaching, eutrophication, or misapplication. Fire retardant's effects on drinking water remain inconclusive. Dilution factors, including water body size, rainfall, and water flow rates lessen the concentration and potency of fire retardant. Wildfire debris (ash and sediment) clog rivers and reservoirs increasing the risk for floods and erosion that ultimately slow and/or damage water treatment systems. There is continued concern of fire retardant effects on land, water, wildlife habitats, and watershed quality, additional research is needed. However, on the positive side, fire retardant (specifically its nitrogen and phosphorus components) has been shown to have a fertilizing effect on nutrient-deprived soils and thus creates a temporary increase in vegetation.

Current USDA procedure maintains that the aerial application of fire retardant in the United States must clear waterways by a minimum of 300 feet in order to safeguard effects of retardant runoff. Aerial uses of fire retardant are required to avoid application near waterways and endangered species (plant and animal habitats). After any incident of fire retardant misapplication, the U.S. Forest Service requires reporting and assessment impacts be made in order to determine mitigation, remediation, and/or restrictions on future retardant uses in that area.

Modeling
Wildfire modeling is concerned with of wildfires in order to comprehend and predict fire behavior. Wildfire modeling aims to aid wildfire suppression, increase the safety of firefighters and the public, and minimize damage. Using, wildfire modeling involves the statistical analysis of past fire events to predict spotting risks and front behavior. Various wildfire propagation models have been proposed in the past, including simple ellipses and egg- and fan-shaped models. Early attempts to determine wildfire behavior assumed terrain and vegetation uniformity. However, the exact behavior of a wildfire's front is dependent on a variety of factors, including windspeed and slope steepness. Modern growth models utilize a combination of past ellipsoidal descriptions and to simulate fire growth as a continuously expanding polygon. may also be used to predict the size of large wildfires. However, large fires that exceed suppression capabilities are often regarded as statistical outliers in standard analyses, even though fire policies are more influenced by large wildfires than by small fires.

Human risk and exposure
Wildfire risk is the chance that a wildfire will start in or reach a particular area and the potential loss of human values if it does. Risk is dependent on variable factors such as human activities, weather patterns, availability of wildfire fuels, and the availability or lack of resources to suppress a fire. Wildfires have continually been a threat to human populations. However, human induced geographical and climatic changes are exposing populations more frequently to wildfires and increasing wildfire risk. It is speculated that the increase in wildfires arises from a century of wildfire suppression coupled with the rapid expansion of human developments into fire-prone wildlands. Wildfires are naturally occurring events that aid in promoting forest health. Global warming and climate changes are causing an increase in temperatures and more droughts nationwide which contributes to an increase in wildfire risk.

Airborne hazards
The most noticeable adverse effect of wildfires is the destruction of property. However, the release of hazardous chemicals from the burning of wildland fuels also significantly impacts health in humans.

Wildfire smoke is composed primarily of carbon dioxide and water vapor. Other common smoke components present in lower concentrations are carbon monoxide, formaldehyde, acrolein, polyaromatic hydrocarbons, and benzene. Small particulates suspended in air which come in solid form or in liquid droplets are also present in smoke. 80 -90% of wildfire smoke, by mass, is within the fine particle size class of 2.5 micrometers in diameter or smaller.

Despite carbon dioxide's high concentration in smoke, it poses a low health risk due to its low toxicity. Rather, carbon monoxide and fine particulate matter, particularly 2.5 µm in diameter and smaller, have been identified as the major health threats. Other chemicals are considered to be significant hazards but are found in concentrations that are too low to cause detectable health effects.

The degree of wildfire smoke exposure to an individual is dependent on the length, severity, duration, and proximity of the fire. People are exposed directly to smoke via the respiratory tract though inhalation of air pollutants. Indirectly, communities are exposed to wildfire debris that can contaminate soil and water supplies.

The (EPA) developed the  (AQI), a public resource that provides national air quality standard concentrations for common air pollutants. The public can use this index as a tool to determine their exposure to hazardous air pollutants based on visibility range.

Fire ecologist Leda Kobziar found that wildfire smoke distributes microbial life on a global level. She stated, "There are numerous allergens that we’ve found in the smoke. And so it may be that some people who are sensitive to smoke have that sensitivity, not only because of the particulate matter and the smoke, but also because there are some biological organisms in it."

Post-fire risks
After a wildfire, hazards remain. Residents returning to their homes may be at risk from falling fire-weakened trees. Humans and pets may also be harmed by falling into s.

Firefighters
Firefighters are at the greatest risk for acute and chronic health effects resulting from wildfire smoke exposure. Due to firefighters' occupational duties, they are frequently exposed to at a close proximity for longer periods of time. A case study on the exposure of wildfire smoke among wildland firefighters shows that firefighters are exposed to significant levels of carbon monoxide and respiratory irritants above -permissible exposure limits (PEL) and ACGIH threshold limit values (TLV). 5–10% are overexposed. The study obtained exposure concentrations for one wildland firefighter over a 10-hour shift spent holding down a fireline. The firefighter was exposed to a wide range of carbon monoxide and respiratory irritant (combination of particulate matter 3.5 µm and smaller, acrolein, and formaldehyde) levels. Carbon monoxide levels reached up to 160ppm and the TLV irritant index value reached a high of 10. In contrast, the OSHA PEL for carbon monoxide is 30ppm and for the TLV respiratory irritant index, the calculated threshold limit value is 1; any value above 1 exceeds exposure limits.

Between 2001 and 2012, over 200 occurred among wildland firefighters. In addition to heat and chemical hazards, firefighters are also at risk for electrocution from power lines; injuries from equipment; ; injuries from vehicle rollovers; ; ; ; and.

Residents
Residents in communities surrounding wildfires are exposed to lower concentrations of chemicals, but they are at a greater risk for indirect exposure through water or soil contamination. Exposure to residents is greatly dependent on individual susceptibility. Vulnerable persons such as children (ages 0–4), the elderly (ages 65 and older), smokers, and pregnant women are at an increased risk due to their already compromised body systems, even when the exposures are present at low chemical concentrations and for relatively short exposure periods. They are also at risk for future wildfires and may move away to areas they consider less risky.

Wildfires affect large numbers of people in Western Canada and the United States. In California alone more than 350,000 people live in towns and cities in "very high fire hazard severity zones".

Fetal exposure
Additionally, there is evidence of an increase in maternal stress, as documented by researchers M.H. O'Donnell and A.M. Behie, thus affecting birth outcomes. In Australia, studies show that male infants born with drastically higher average birth weights were born in mostly severely fire-affected areas. This is attributed to the fact that maternal signals directly affect fetal growth patterns.

Asthma is one of the most common chronic disease among children in the United States affecting estimated 6.2 million children. A recent area of research on asthma risk focuses specifically on the risk of air pollution during the gestational period. Several pathophysiology processes are involved are in this. In human's considerable airway development occurs during the 2nd and 3rd trimester and continue until 3 years of age. It is hypothesized that exposure to these toxins during this period could have consequential effects as the epithelium of the lungs during this time could have increased permeability to toxins. Exposure to air pollution during parental and pre-natal stage could induce epigenetic changes which are responsible for the development of asthma. Recent Meta-Analyses have found significant association between PM2.5, NO2 and development of asthma during childhood despite heterogeneity among studies. Furthermore, maternal exposure to chronic stressor, which are most like to be present in distressed communities, which is also a relevant co relate of childhood asthma which may further help explain the early childhood exposure to air pollution, neighborhood poverty and childhood risk. Living in distressed neighborhood is not only linked to pollutant source location and exposure but can also be associated with degree of magnitude of chronic individual stress which can in turn alter the allostatic load of the maternal immune system leading to adverse outcomes in children, including increased susceptibility to air pollution and other hazards.

Health effects
Wildfire smoke contains particulate matter that may have adverse effects upon the human respiratory system. Evidence of the health effects of wildfire smoke should be relayed to the public so that exposure may be limited. Evidence of health effects can also be used to influence policy to promote positive health outcomes.

Inhalation of smoke from a wildfire can be a health hazard. Wildfire smoke is composed of combustion products i.e., , , , organic chemicals, s and other compounds. The principal health concern is the inhalation of particulate matter and carbon monoxide.

Particulate matter (PM) is a type of air pollution made up of particles of dust and liquid droplets. They are characterized into three categories based on the diameter of the particle: coarse PM, fine PM, and ultrafine PM. Coarse particles are between 2.5 micrometers and 10 micrometers, fine particles measure 0.1 to 2.5 micrometers, and ultrafine particle are less than 0.1 micrometer. Each size can enter the body through inhalation, but the PM impact on the body varies by size. Coarse particles are filtered by the upper airways and these particles can accumulate and cause pulmonary inflammation. This can result in eye and sinus irritation as well as sore throat and coughing. Coarse PM is often composed of materials that are heavier and more toxic that lead to short-term effects with stronger impact.

Smaller particulate moves further into the respiratory system creating issues deep into the lungs and the bloodstream. In asthma patients, PM2.5 causes inflammation but also increases oxidative stress in the epithelial cells. These particulates also cause apoptosis and autophagy in lung epithelial cells. Both processes cause the cells to be damaged and impacts the cell function. This damage impacts those with respiratory conditions such as asthma where the lung tissues and function are already compromised. The third PM type is ultra-fine PM (UFP). UFP can enter the bloodstream like PM2.5 however studies show that it works into the blood much quicker. The inflammation and epithelial damage done by UFP has also shown to be much more severe. PM2.5 is of the largest concern in regards to wildfire. This is particularly hazardous to the very young, elderly and those with chronic conditions such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis and cardiovascular conditions. The illnesses most commonly with exposure to fine particle from wildfire smoke are bronchitis, exacerbation of asthma or COPD, and pneumonia. Symptoms of these complications include wheezing and shortness of breath and cardiovascular symptoms include chest pain, rapid heart rate and fatigue.

Asthma exacerbation
Smoke from wildfires can cause health problems, especially for children and those who already have respiratory problems. Several epidemiological studies have demonstrated a close association between and respiratory allergic diseases such as bronchial.

An observational study of smoke exposure related to the 2007 San Diego wildfires revealed an increase both in healthcare utilization and respiratory diagnoses, especially among the group sampled. Projected climate scenarios of wildfire occurrences predict significant increases in respiratory conditions among young children. triggers a series of biological processes including inflammatory immune response,, which are associated with harmful changes in allergic respiratory diseases.

Although some studies demonstrated no significant acute changes in lung function among people with related to PM from wildfires, a possible explanation for these counterintuitive findings is the increased use of, such as inhalers, in response to elevated levels of smoke among those already diagnosed with. In investigating the association of medication use for obstructive lung disease and wildfire exposure, researchers found increases both in the usage of inhalers and initiation of long-term control as in oral steroids. More specifically, some people with reported higher use of  (inhalers). After two major wildfires in California, researchers found an increase in physician prescriptions for in the years following the wildfires than compared to the year before each occurrence.

There is consistent evidence between wildfire smoke and the exacerbation of asthma.

Carbon monoxide danger
Carbon monoxide (CO) is a colorless, odorless gas that can be found at the highest concentration at close proximity to a smoldering fire. For this reason, carbon monoxide inhalation is a serious threat to the health of wildfire firefighters. CO in smoke can be inhaled into the lungs where it is absorbed into the bloodstream and reduces oxygen delivery to the body's vital organs. At high concentrations, it can cause headache, weakness, dizziness, confusion, nausea, disorientation, visual impairment, coma and even death. However, even at lower concentrations, such as those found at wildfires, individuals with cardiovascular disease may experience chest pain and cardiac arrhythmia. A recent study tracking the number and cause of wildfire firefighter deaths from 1990–2006 found that 21.9% of the deaths occurred from heart attacks.

Another important and somewhat less obvious health effect of wildfires is psychiatric diseases and disorders. Both adults and children from countries ranging from the United States and Canada to Greece and Australia who were directly and indirectly affected by wildfires were found by researchers to demonstrate several different mental conditions linked to their experience with the wildfires. These include (PTSD),, anxiety, and s.

In a new twist to wildfire health effects, former uranium mining sites were burned over in the summer of 2012 near North Fork, Idaho. This prompted concern from area residents and Idaho State Department of Environmental Quality officials over the potential spread of radiation in the resultant smoke, since those sites had never been completely cleaned up from radioactive remains.

Epidemiology
The western US has seen an increase in both frequency and intensity of wildfires over the last several decades. This increase has been attributed to the arid climate of the western US and the effects of global warming. An estimated 46 million people were exposed to wildfire smoke from 2004 to 2009 in the Western United States. Evidence has demonstrated that wildfire smoke can increase levels of particulate matter in the atmosphere.

The EPA has defined acceptable concentrations of particulate matter in the air, through the National Ambient Air Quality Standards and monitoring of ambient air quality has been mandated. Due to these monitoring programs and the incidence of several large wildfires near populated areas, epidemiological studies have been conducted and demonstrate an association between human health effects and an increase in fine particulate matter due to wildfire smoke.

The EPA has defined acceptable concentrations of particulate matter in the air. The National Ambient Air Quality Standards are part of the Clean Air Act and provide mandated guidelines for pollutant levels and the monitoring of ambient air quality. In addition to these monitoring programs, the increased incidence of wildfires near populated areas have precipitated several epidemiological studies. Such studies have demonstrated an association between negative human health effects and an increase in fine particulate matter due to wildfire smoke. The size of the particulate matter is significant as smaller particulate matter (fine) is easily inhaled into the human respiratory tract. Often, small particulate matter can be inhaled into deep lung tissue causing respiratory distress, illness, or disease.

An increase in PM smoke emitted from the Hayman fire in Colorado in June 2002, was associated with an increase in respiratory symptoms in patients with COPD. Looking at the wildfires in Southern California in October 2003 in a similar manner, investigators have shown an increase in hospital admissions due to asthma symptoms while being exposed to peak concentrations of PM in smoke. Another epidemiological study found a 7.2% (95% confidence interval: 0.25%, 15%) increase in risk of respiratory related hospital admissions during smoke wave days with high wildfire-specific particulate matter 2.5 compared to matched non-smoke-wave days.

Children participating in the Children's Health Study were also found to have an increase in eye and respiratory symptoms, medication use and physician visits. Recently, it was demonstrated that mothers who were pregnant during the fires gave birth to babies with a slightly reduced average birth weight compared to those who were not exposed to wildfire during birth. Suggesting that pregnant women may also be at greater risk to adverse effects from wildfire. Worldwide it is estimated that 339,000 people die due to the effects of wildfire smoke each year.

While the size of particulate matter is an important consideration for health effects, the chemical composition of particulate matter (PM2.5) from wildfire smoke should also be considered. Antecedent studies have demonstrated that the chemical composition of PM2.5 from wildfire smoke can yield different estimates of human health outcomes as compared to other sources of smoke. Health outcomes for people exposed to wildfire smoke may differ from those exposed to smoke from alternative sources such as solid fuels.