A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of combustible vegetation.
Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire (in Australia), desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire. Some natural forest ecosystems Fire ecology. Modern forest management often engages in prescribed burns to mitigate fire risk and promote natural forest cycles. However, controlled burns can turn into wildfires by mistake.Wildfires can be classified by cause of ignition, physical properties, combustible material present, and the effect of weather on the fire. Wildfire severity results from a combination of factors such as available fuels, physical setting, and weather.Graham, et al., 12, 36 National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, 4–6. Climatic cycles with wet periods that create substantial fuels, followed by drought and heat, often precede severe wildfires. These cycles have been intensified by climate change,Parmesan, C., M.D. Morecroft, Y. Trisurat, R. Adrian, G.Z. Anshari, A. Arneth, Q. Gao, P. Gonzalez, R. Harris, J. Price, N. Stevens, and G.H. Talukdarr, 2022: Chapter 2: Terrestrial and Freshwater Ecosystems and Their Services . In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
Wildfires are a common type of Natural disaster in some regions, including Siberia (Russia); California, Washington, Oregon, Texas, Florida (United States); British Columbia (Canada); and Australia. Areas with Mediterranean climates or in the taiga biome are particularly susceptible. Wildfires can severely impact humans and their settlements. Effects include for example the direct health impacts of smoke and fire, as well as destruction of property (especially in wildland–urban interfaces), and economic losses. There is also the potential for contamination of water and soil.
At a global level, human practices have made the impacts of wildfire worse, with a doubling in land area burned by wildfires compared to natural levels. Humans have impacted wildfire through climate change (e.g. more intense and ), land-use change, and wildfire suppression. The carbon released from wildfires can add to carbon dioxide concentrations in the atmosphere and thus contribute to the greenhouse effect. This creates a climate change feedback.
Naturally occurring wildfires can have beneficial effects on those that have evolved with fire.
In fact, many plant species depend on the effects of fire for growth and reproduction.
In middle latitudes, the most common human causes of wildfires are equipment generating sparks (chainsaws, grinders, mowers, etc.), overhead power lines, and arson.
Arson may account for over 20% of human caused fires. However, in the 2019–20 Australian bushfire season "an independent study found online Internet bot and trolls exaggerating the role of arson in the fires." In the 2023 Canadian wildfires false claims of arson gained traction on social media; however, arson is generally not a main cause of wildfires in Canada. In California, generally 6–10% of wildfires annually are arson.
Coal seam fires burn in the thousands around the world, such as those in Burning Mountain, New South Wales; Centralia, Pennsylvania; and several coal-sustained fires in China. They can also flare up unexpectedly and ignite nearby flammable material.
Dense forests usually provide more shade, resulting in lower ambient temperatures and greater humidity, and are therefore less susceptible to wildfires.Graham, et al., 12. 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. National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, 3. Plants continuously lose water by evapotranspiration, but water loss is usually balanced by water absorbed from the soil, humidity, or rain. When this balance is not maintained, often as a consequence of , plants dry out and are therefore more flammable.
A wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the transition between unburned and burned material. Glossary of Wildland Fire Terminology, 74. As the front approaches, the fire heats both the surrounding air and woody material through convection and thermal radiation. First, wood is dried as water is vaporized at a temperature of . Next, the pyrolysis of wood at releases flammable gases. Finally, wood can smolder at or, when heated sufficiently, ignite at .de Sousa Costa and Sandberg, 229–230. Even before the flames of a wildfire arrive at a particular location, heat transfer from the wildfire front warms the air to , 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 flashover or torching: the drying of tree canopies and their subsequent ignition from below.Graham, et al., 10–11.
Wildfires have a rapid ''forward rate of spread'' (FROS) when burning through dense uninterrupted fuels. They can move as fast as in forests and in grasslands.Billing, 5–6 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''.Graham, ''et al''., 12 They may also spread by ''jumping'' or ''spotting'' as winds and vertical [[convection]] columns carry ''firebrands'' (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as [[firebreak]]s.Graham, ''et al''., 16. Torching and fires in tree canopies encourage spotting, and dry ground fuels around a wildfire are especially vulnerable to ignition from firebrands.Graham, ''et al''., 9, 16. 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 from the fire front.(2010). 9780980740820, Victorian Bushfires Royal Commission, Australia. ISBN 9780980740820
Especially large wildfires may affect air currents in their immediate vicinities by the stack effect: air rises as it is heated, and large wildfires create powerful that will advection new, cooler air from surrounding areas in . National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, 4. Great vertical differences in temperature and humidity encourage pyrocumulus clouds, strong winds, and with the force of tornadoes at speeds of more than .Graham, et al., 16–17.Olson, et al., 2 Rapid rates of spread, prolific crowning or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions. Glossary of Wildland Fire Terminology, 69.
Weather conditions are raising the risks of wildfires. But the total area burnt by wildfires has decreased. This is mostly because savanna has been converted to Croplands, so there are fewer trees to burn.
Climate variability including , , and El Niño, and regional weather patterns, such as high-pressure ridges, can increase the risk and alter the behavior of wildfires dramatically.McKenzie, et al., 893 Years of high precipitation can produce rapid vegetation growth, which when followed by warmer periods can encourage more widespread fires and longer fire seasons.Graham, et al., 2 High temperatures dry out the fuel loads and make them more flammable, increasing tree mortality and posing significant risks to global forest health. Since the mid-1980s, in the Western US, 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. A 2019 study indicates that the increase in California fires may be partially attributable to human-induced climate change.
In the summer of 1974–1975 (southern hemisphere), Australia suffered its worst recorded wildfire, when 15% of Australia's land mass suffered "extensive fire damage". Fires that summer burned up an estimated . In Australia, the annual number of hot days (above ) and very hot days (above ) has increased significantly in many areas of the country since 1950. The country has always had bushfires but in 2019, the extent and ferocity of these fires increased dramatically. As Smoke From Bushfires Chokes Sydney, Australian Prime Minister Dodges on Climate Change , Time 21 November 2019. For the first time catastrophic bushfire conditions were declared for Greater Sydney. New South Wales and Queensland declared a state of emergency but fires were also burning in South Australia and Western Australia. The facts about bushfires and climate change , Climate Council, 13 November 2019
In 2019, extreme heat and dryness caused massive wildfires in Siberia, Alaska, Canary Islands, Australia, and in the Amazon rainforest. 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.
As of August 2020, the wildfires in that year were 13% worse than in 2019 due primarily to climate change, deforestation and agricultural burning. The Amazon rainforest's existence is threatened by fires. Record-breaking wildfires in 2021 occurred in Turkey, Greece and Russia, thought to be linked to climate change. are linked to fire-season severity.]]
Wildfires release large amounts of carbon dioxide, black and brown carbon particles, and ozone precursors such as volatile organic compounds and NOx into the atmosphere. These emissions affect radiation, clouds, and climate on regional and even global scales. Wildfires also emit substantial amounts of semi-volatile organic species that can partition from the gas phase to form secondary organic aerosol (SOA) over hours to days after emission. In addition, the formation of the other pollutants as the air is transported can lead to harmful exposures for populations in regions far away from the wildfires. While direct emissions of harmful pollutants can affect first responders and residents, wildfire smoke can also be transported over long distances and impact air quality across local, regional, and global scales., United States, in 2013. The Rim Fire burned more than of forest.]]The health effects of wildfire smoke, such as worsening cardiovascular and respiratory conditions, extend beyond immediate exposure, contributing to nearly 16,000 annual deaths, a number expected to rise to 30,000 by 2050. The economic impact is also significant, with projected costs reaching $240 billion annually by 2050, surpassing other climate-related damages.
Over the past century, wildfires have accounted for 20–25% of global carbon emissions, the remainder from human activities. Global carbon emissions from wildfires through August 2020 equaled the average annual emissions of the European Union. In 2020, the carbon released by California's wildfires was significantly larger than the state's other carbon emissions.
Forest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigatonnes (0.89 and 2.83 billion ) of CO2 into the atmosphere, which is between 13–40% of the annual global carbon dioxide emissions from burning fossil fuels.
In June and July 2019, fires in the Arctic emitted more than 140 megatons of carbon dioxide, according to an analysis by CAMS. To put that into perspective this amounts to the same amount of carbon emitted by 36 million cars in a year. The recent wildfires and their massive CO2 emissions mean that it will be important to take them into consideration when implementing measures for reaching greenhouse gas reduction targets accorded with the Paris climate agreement. Due to the complex oxidative chemistry occurring during the transport of wildfire smoke in the atmosphere, the toxicity of emissions was indicated to increase over time.
Atmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15%. The Amazon is estimated to hold around 90 billion tons of carbon. As of 2019, the earth's atmosphere has 415 parts per million of carbon, and the destruction of the Amazon would add about 38 parts per million.
Some research has shown wildfire smoke can have a cooling effect.
Research in 2007 stated that black carbon in snow changed temperature three times more than atmospheric carbon dioxide. As much as 94 percent of Arctic warming may be caused by dark carbon on snow that initiates melting. The dark carbon comes from fossil fuels burning, wood and other biofuels, and forest fires. Melting can occur even at low concentrations of dark carbon (below five parts per billion).
Wildfire prevention programs around the world may employ techniques such as wildland fire use (WFU) and prescribed or . 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. Other objectives can include maintenance of healthy forests, rangelands, and wetlands, and support of ecosystem diversity.
Strategies for wildfire prevention, detection, control and suppression have varied over the years. One common and inexpensive technique to reduce the risk of uncontrolled wildfires is : intentionally igniting smaller less-intense fires to minimize the amount of flammable material available for a potential wildfire. Interagency Strategy for the Implementation of the Federal Wildland Fire Policy, entire text National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management, entire text Vegetation may be burned periodically to limit the accumulation of plants and other debris that may serve as fuel, while also maintaining high species diversity. Fire. The Australian Experience, 5–6.Graham, et al., 15. While other people claim that controlled burns and a policy of allowing some wildfires to burn is the cheapest method and an ecologically appropriate policy for many forests, they tend not to take into account the economic value of resources that are consumed by the fire, especially merchantable timber. Some studies conclude that while fuels may also be removed by logging, such thinning treatments may not be effective at reducing fire severity under extreme weather conditions.
Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure. Communities in the Philippines also maintain wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather.Karki, 14. 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.
Public hotlines, 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 asthenopia, 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. These systems may be semi- or fully automated and employ systems based on the risk area and degree of human presence, as suggested by GIS data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via Global Positioning System (GPS) into a collective whole for near-realtime use by wireless Incident Command Centers.
The Department of Natural Resources signed a contract with PanoAI for the installation of 360 degree 'rapid detection' cameras around the Pacific northwest, which are mounted on cell towers and are capable of continuous monitoring of a radius. Additionally, Sensaio Tech, based in Brazil and Toronto, has released a sensor device that continuously monitors 14 different variables common in forests, ranging from soil temperature to salinity. This information is connected live back to clients through dashboard visualizations, while mobile notifications are provided regarding dangerous levels.
In 2015 a new fire detection tool is in operation at the U.S. Department of Agriculture (USDA) Forest Service (USFS) which uses data from the Suomi NPP (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.
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 375 m fire product, put it to use during several large wildfires in Kruger.
Since 2021 NASA has provided active fire locations in near real-time via the Fire Information for Resource Management System (FIRMS).
The increased prevalence of wildfires has led to proposals deploy technologies based on artificial intelligence for early detection, prevention, and prediction of wildfires.
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 Mann Gulch fire in Montana, United States, thirteen died when they lost their communication links, became disoriented, and were overtaken by the fire. In the Australian February 2009 Victorian bushfires, at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.
Especially in hot weather conditions, 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 heat stroke. Various factors can contribute to the risks posed by heat stress, including strenuous work, personal risk factors such as age and Physical fitness, dehydration, sleep deprivation, and burdensome personal protective equipment. 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 for wildland firefighters. The smoke and dust from wildfires can contain gases such as carbon monoxide, sulfur dioxide and formaldehyde, as well as particulates such as Wood ash and silica. 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. Firefighters 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 firefighters face include slips, trips, 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.
Typical fire retardants contain the same agents as fertilizers. Fire retardants 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.
Wildfires can affect local atmospheric pollution, and release carbon in the form of carbon dioxide. Wildfire emissions contain fine particulate matter which can cause cardiovascular and respiratory problems. Increased fire byproducts in the troposphere can increase ozone concentrations beyond safe levels.
High-severity wildfire creates complex early seral forest habitat (also called "snag forest habitat"), which often has higher species richness and diversity than unburned old forest.
Although some ecosystems rely on naturally occurring fires to regulate growth, some ecosystems suffer 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 ordinarily fire-dependent areas has upset natural cycles, damaged native plant communities, and encouraged the growth of non-native weeds. Interagency Strategy for the Implementation of the Federal Wildland Fire Policy, 3, 37.Graham, et al., 3. Invasive species, such as Lygodium microphyllum and Bromus tectorum, 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 positive feedback loop that increases fire frequency and further alters native vegetation communities.
In the Amazon rainforest, drought, logging, cattle ranching practices, and slash-and-burn agriculture damage fire-resistant forests and promote the growth of flammable brush, creating a cycle that encourages more burning.Nepstad, 4, 8–11 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 2030.Nepstad, 4 Wildfires generate ash, reduce the availability of organic nutrients, and cause an increase in water runoff, eroding other nutrients and creating flash flood conditions. A 2003 wildfire in the North Yorkshire Moors burned off of Ericaceae and the underlying peat layers. Afterwards, wind erosion stripped the ash and the exposed soil, revealing archaeological remains dating 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.
Benzene is one of many chemicals that have been found in drinking water systems after wildfires. Benzene can permeate certain plastic pipes and thus require long times to be removed from the water distribution infrastructure. Researchers estimated that, in worst case scenarios, more than 286 days of constant flushing of a contaminated HDPE service line were needed to reduce benzene below safe drinking water limits. Temperature increases caused by fires, including wildfires, can cause plastic water pipes to generate toxic chemicals such as benzene.
Wildfire smoke is composed primarily of carbon dioxide and water vapor. Other common components present in lower concentrations are carbon monoxide, formaldehyde, acrolein, polyaromatic hydrocarbons, and benzene. Small airborne particulates (in solid form or liquid droplets) are also present in smoke and ash debris. 80–90% of wildfire smoke, by mass, is within the fine particle size class of 2.5 micrometers in diameter or smaller.
Carbon dioxide in smoke 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. High levels of heavy metals, including lead, arsenic, cadmium, and copper were found in the ash debris following the 2007 Californian wildfires. A national clean-up campaign was organised in fear of the health effects from exposure. In the devastating California Camp Fire (2018) that killed 85 people, lead levels increased by around 50 times in the hours following the fire at a site nearby (Chico). Zinc concentration also increased significantly in Modesto, away. Heavy metals such as manganese and calcium were found in numerous California fires as well. 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 through inhalation of air pollutants. Indirectly, communities are exposed to wildfire debris that can contaminate soil and water supplies.
The U.S. Environmental Protection Agency (EPA) developed the air quality index (AQI), a public resource that provides national air quality standard concentrations for common air pollutants. The public can use it to determine their exposure to hazardous air pollutants based on visibility range.
Inhalation of smoke from a wildfire can be a health hazard. Wildfire smoke is composed of combustion products i.e. carbon dioxide, carbon monoxide, water vapor, particulate matter, organic chemicals, 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 particle diameter: 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. lmpact on the body upon inhalation varies by size. Coarse PM is filtered by the upper airways and 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 heavier and more toxic materials that lead to short-term effects with stronger impact.
Smaller PM 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 damage the cells and impact cell function. This damage impacts those with respiratory conditions such as asthma where the lung tissues and function are already compromised. Particulates less than 0.1 micrometer are called ultrafine particle (UFP). It is a major component of wildfire smoke. UFP can enter the bloodstream like PM2.5–0.1 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 associated with exposure to fine PM 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.
An observational study of smoke exposure related to the 2007 San Diego wildfires revealed an increase both in healthcare utilization and respiratory diagnoses, especially asthma among the group sampled. Projected climate scenarios of wildfire occurrences predict significant increases in respiratory conditions among young children. PM triggers a series of biological processes including inflammatory immune response, oxidative stress, which are associated with harmful changes in allergic respiratory diseases.
Although some studies demonstrated no significant acute changes in lung function among people with asthma related to PM from wildfires, a possible explanation for these counterintuitive findings is the increased use of Asthma, such as inhalers, in response to elevated levels of smoke among those already diagnosed with asthma.
There is consistent evidence between wildfire smoke and the exacerbation of asthma.
Asthma is one of the most common chronic disease among children in the United States, affecting an estimated 6.2 million children. Research on asthma risk focuses specifically on the risk of air pollution during the gestational period. Several pathophysiology processes are involved in this. Considerable airway development occurs during the 2nd and 3rd trimesters and continues 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. Studies have found significant association between PM2.5, NO2 and development of asthma during childhood despite heterogeneity among studies. Furthermore, maternal exposure to chronic stressors is most likely present in distressed communities, and as this can be correlated with childhood asthma, it may further explain links between early childhood exposure to air pollution, neighborhood poverty, and childhood risk.
Another important and somewhat less obvious health effect of wildfires is psychiatric diseases and disorders. Both adults and children from various countries who were directly and indirectly affected by wildfires were found to demonstrate different mental conditions linked to their experience with the wildfires. These include post-traumatic stress disorder (PTSD), depression, anxiety, and .
The EPA has defined acceptable concentrations of PM 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.
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 2003, 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. 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. 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.
Besides the size of PM, their chemical composition 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 such as solid fuels.
Chemically contaminated drinking water, at levels of hazardous waste concern, is a growing problem. In particular, hazardous waste scale chemical contamination of buried water systems was first discovered in the U.S. in 2017, and has since been increasingly documented in Hawaii, Colorado, and Oregon after wildfires. In 2021, Canadian authorities adapted their post-fire public safety investigation approaches in British Columbia to screen for this risk, but have not found it as of 2023. Another challenge is that private drinking wells and the plumbing within a building can also become chemically contaminated and unsafe. Households experience a wide-variety of significant economic and health impacts related to this contaminated water. Evidence-based guidance on how to inspect and test wildfire impacted wells and building water systems was developed for the first time in 2020. In Paradise, California, for example, the 2018 Camp Fire caused more than $150 million dollars worth of damage. This required almost a year of time to decontaminate and repair the municipal drinking water system from wildfire damage.
The source of this contamination was first proposed after the 2018 Camp Fire in California as originating from thermally degraded plastics in water systems, smoke and vapors entering depressurized plumbing, and contaminated water in buildings being sucked into the municipal water system. In 2020, it was first shown that thermal degradation of plastic drinking water materials was one potential contamination source. In 2023, the second theory was confirmed where contamination could be sucked into pipes that lost water pressure.
Other post-fire risks, can increase if other extreme weather follows. For example, wildfires make soil less able to absorb precipitation, so heavy rainfall can result in more severe flooding and damages like .
Between 2001 and 2012, over 200 fatalities occurred among wildland firefighters. In addition to heat and chemical hazards, firefighters are also at risk for electrocution from power lines; injuries from equipment; slips, trips, and falls; injuries from vehicle rollovers; Heat illness; insect bites and stings; stress; and rhabdomyolysis. Wildfires that reach urban environments create additional toxic fumes and carcinogenic particles from burning metals, plastics, electronics, paints, and other common materials.
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".
Direct risks to building residents in fire-prone areas can be moderated through design choices such as choosing fire-resistant vegetation, maintaining landscaping to avoid debris accumulation and to create firebreaks, and by selecting fire-retardant roofing materials. Potential compounding issues with poor air quality and heat during warmer months may be addressed with MERV 11 or higher outdoor air filtration in building ventilation systems, mechanical cooling, and a provision of a refuge area with additional air cleaning and cooling, if needed.
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 progymnosperm forests. Lepidodendron forests dating to the Carboniferous period have charred peaks, evidence of crown fires. In Jurassic gymnosperm forests, there is evidence of high frequency, light surface fires. The increase of fire activity in the late TertiaryHistorically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. The 2009 version of the ICS time chart recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status. is possibly due to the increase of C4-type grasses. As these grasses shifted to more , their high flammability increased fire frequency, promoting grasslands over woodlands.Pausas and Keeley, 595 However, fire-prone habitats may have contributed to the prominence of trees such as those of the genera Eucalyptus, Pinus and Sequoia, which have thick bark to withstand fires and employ pyriscence.Pausas and Keeley, 596 "Redwood Trees" .
Wildfires typically occur during periods of increased temperature and drought. An increase in fire-related debris flow in of northeastern Yellowstone National Park was linked to the period between AD 1050 and 1200, coinciding with the Medieval Warm Period. However, human influence caused an increase in fire frequency. Dendrochronological fire scar data and charcoal layer data in Finland 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.Pitkänen, et al., 15–16 and 27–30 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. University of Oregon Summary, accessed 2 February 2010 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 journal Science, the number of natural and human-caused fires decreased by 24.3% between 1998 and 2015. Researchers explain this as a transition from nomadism to settled lifestyle and intensification of agriculture that lead to a drop in the use of fire for land clearing.
Increases of certain tree species (i.e. conifers) over others (i.e. ) can increase wildfire risk, especially if these trees are also planted in . Some invasive species, moved in by humans (i.e., for the pulp and paper industry) have in some cases also increased the intensity of wildfires. Examples include species such as Eucalyptus in California and gamba grass in Australia.
Wildfire activity has been attributed as a major factor in the development of Ancient Greece. In modern Greece, as in many other regions, it is the most common Natural disaster and figures prominently in the social and economic lives of its people.
In 1937, U.S. President Franklin D. Roosevelt initiated a nationwide fire prevention campaign, highlighting the role of human carelessness in forest fires. Later posters of the program featured Uncle Sam, characters from the Disney movie Bambi, and the official mascot of the U.S. Forest Service, Smokey Bear. The Smokey Bear fire prevention campaign has yielded one of the most popular characters in the United States; for many years there was a living Smokey Bear mascot, and it has been commemorated on postage stamps.
There are also significant indirect or second-order societal impacts from wildfire, such as demands on utilities to prevent power transmission equipment from becoming ignition sources, and the cancelation or nonrenewal of homeowners insurance for residents living in wildfire-prone areas.
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