Wildfires

What is wildfire?

Wildfires are unplanned fires that occur in wildlands such as forest, rangelands or grasslands. They can occur naturally (ignited by lightning), or be caused by human activities such as campfires, faulty power lines, and burning crop residues. Other than those ignition sources, wildfires also need fuels and the proper meteorological condition to start and spread.

Fuels refer to anything that can burn, trees, bushes, grasses, fallen leaves. The availability of fuel is determined in large part by management practices and ecosystem processes and . For example, deforestation leaves behind slash, which are highly inflammable. Expansion of fire-resistant invasive annual grasses is one of the dominant factor in largely increasing the number, frequency, and severity of rangeland wildfires in the Northwest.

Meteorological conditions, specifically high temperature, low humidity, and wind play a significant role in triggering and sustaining a fire.

• Low Humidity: Low humidity levels dry out vegetation, making it more susceptible to ignition and promoting the rapid spread of fires.
• High Temperatures: Hot temperatures contribute to the drying of vegetation, creating favorable conditions for fires.
• Wind: Wind can carry embers over long distances, accelerate the spread of flames, and make firefighting efforts more challenging.

Wildfires under climate change

Wildfire activities have significantly increased in the past decades in Alaska and the western United States. Statistics show that the number of large fire occurrences, fire extent, fire severity, and fire season length have all increased since 1980. These changes are closely related to climate change both directly and indirectly.

Climate change drives increase in fire activity directly by inducing higher temperatures, reduced winter snowpack, earlier snowmelt, decreased summer precipitation, and increased evaporation. These conditions creates a more favorable condition for the start and spread of wildfires.

Indirectly, climate change drives those changes in wildfire by changing the ecosystems. For example, climate change degrades forest, creates conditions that favor the expansion of fire-resistant invasive species, and promotes beetle outbreaks that have killed millions of acres of trees and resulted in more flammable fuels.

As climate change continues, we can expect wildfire activity to increase, with rising temperatures and persistent droughts affecting wildland ecosystems​.

Impacts of wildfire

Wildfires have significant impacts on environment, human health, and infrastructure. (Drought has extensive impacts across multiple sectors, affecting ecosystems, agriculture, water resources, energy production, commerce, public health, and infrastructure stability.)

• Public Health Wildfire smoke, which contains various air pollutants, poses a major public health risk, primarily due to particulate matter (PM2.5). Inhalation of smoke and this fine particulate matter produced by wildfires causes respiratory issues. These issues can range from irritation of the respiratory system (nose, mouth, throat, and lungs) to serious problems like bronchitis or asthma. The lack of oxygen from inhaling smoke, humans can experience serious cardiovascular issues, including heart attack or heart failure, because of wildfires.
• Ecosystem and Biodiversity Wildfires will likely change the forests composition. Frequent fires can hinder the regeneration of certain tree species, allowing shrubs and grasses to dominate for extended periods. Frequent fire will also likely reduce the abundance of shade-tolerant species and gradually lead to forests dominated by fire-resistant species, such as Douglas-fir and western larch, instead of fire-susceptible species like western hemlock and subalpine fir. Additionally, increase in fire frequency will also likely result in more young forests as older, late-successional forests burn. Frequent fires will likely replace native plants by invasive annual grassland as invasive grasses produce many seeds and can reestablish more quickly after a wildfire. All these changes will change the number and composition of animal species that depend on forests or grasslands as their habitat, which, in turn, may affect the cultural values, as well as the experience of hunters, anglers, and recreationalists.

• Livestock: Wildfires impact livestock by disrupting grazing rotations, stocking rates, and rangeland management. They directly damage grazing land, often leading to the closure of public grazing allotments for several years to allow for restoration. This forces ranchers and rangeland managers to find alternative, often costly and time-consuming, sources of summer forage. Additionally, wildfires promote the expansion of invasive annual grasses, which outcompete native grasses that provide late-season forage, further reducing the availability of palatable forage for livestock.
• Water resources Wildfires can contaminate water quality and impact water supply within watersheds.They bring more sediments, eroded soil, ashes and debris from fires, as well as heavy metals and toxins into nearby water sources. These substances pollute the water and make it unsafe for human or animal consumption, as well as disrupt or destroy aquatic life. Additionally, decreased vegetation increases runoff, reduces groundwater recharge, and diminishes overall water availability.
• Buildings and other key infrastructures Though started in the wildland, wildfires can easily spread and cause large damages to both residential and industrial infrastructures. For example, the Camp Fire occurred in Northern California in November 2018 destroyed more than 18,000 structures, including nearly 14,000 homes, and significant damage to critical infrastructure such as power lines, roads, and communication networks. Roads and highways can also be impacted by the heat, flames, and falling debris and became impassable.
• Power and Energy Wildfires severely impact the power and energy sector by damaging or destroying energy infrastructure, such as power lines, power plants, transformers, and substations. They also disrupt operations through Public Safety Power Shutoffs. While these shutdowns effectively reduce the likelihood of ignition, they are extremely costly. For example, a study by a scholar at the Stanford Woods Institute for the Environment estimated that the PSPS in October 2019 cost California’s economy up to $2.5 billion.

Wildfire Data

Historical data

U.S. Wildfires:

The annual Incident Management Situation Report by The National Interagency Coordination Center provides comprehensive statistics on various aspects from 1983 to the present, including burned areas, number of human-caused and lightning-caused fires, detailed suppression and mobilization cost. The following statistics are explicitly extracted and provided:

• US total burned areas and number of fires
• US total suppression cost
• Number of lightning-caused fires by geographic area
• Number of human-caused fires by geographic area
• Combined wildfire datasets for the US and certain territories 1878-2019

MTBS multi-agency project maintains a database of wildfire occurrence and burned areas by state.

Global fires:

• The statistics portal by Global Wildfire Information System (GWIS) offers the number of fires, burned area, as well as their seasonal trend by country. Its Country Profile provides detailed information of numbers of fires, burned area, emission etc. by landcover class for all countries for years 2002-2023. Our World in Data visualizes some of these statistics in chart.
• Global Fire Emissions Database (GFED v4) provides global estimates of monthly burned area, monthly emissions and fractional contributions of different fire types. Data is at 0.25-degree resolution and is available from June 1995 through 2016.
• Fire danger indices at 0.25-degree produced by the European Forest Fire Information System (EFFIS). This data provides complete historical reconstruction of meteorological conditions favorable to the start, spread, and sustainability of fire.

Real-time Monitoring

• Active fires (MODIS and VIIRS)
• Burnt Areas (MODIS and VIIRS NRT)
• Real-time Hot Dry Windy Index (HDWI; an indicator of wildfire spread)

Near-term (1-7 days ahead) forecast

• Monthly and seasonal forecast of temperature and precipitation by regions

• Fire danger forecast 1 day aheadby GWIS.
• US 7-day fire potential forecastproduced by a fire potential model by NICC
• US 7-day fire danger (including fire potential index, large fire probability, fire spread probability) forecast by USGS, produced by feeding satellite observations and weather forecast into a fuel model

Forecast at the monthly to seasonal scale

• US seasonal fire outlookby NICC
• FuelCast provides monthly fuel and fire forecasts during the growing season to help users stay up to date on fire danger. It is updated monthly during the growing season.

Future projection for one year ahead and beyond

• Great Basin Rangeland Fire Probability Map represents the relative probability of large (> 1,000 acres) rangeland fire given an ignition in a given year. Maps are updated yearly.
• CMIP6 is currently the leading state-of-the-art resource for future climate projections. The data can be downloaded from http://esgf-node.llnl.gov/search/cmip6/. Navigating the data portal and finding the necessary variables can be challenging, so we provide some guidance below:

Filter with Facets	Value	Explanation
Classifications --> Realm	"land"	land component of CMIP6 model
Classifications --> Variable ID	"burntFractionAll"	burnt area fraction
Identifiers --> Experiment ID	"esm-hist" or "hist"	historical simulation
	"esm-piControl" or "piControl"	pre-industrial simulation
	"SSP119"	1.5 degree Paris Agreement goal
	"SSP126"	sustainable pathway
	"SSP245"	middle of the road
	"SSP585"	fossil fuel-rich development
Resolutions --> Nominal Resolution	choose your desired option from the available selections after applying the above filters.

• Note that the resolution of CMIP6 simulations (coarser than 100 km for most models) is usually too coarse for climate risk analysis and other downstream applications, the downscaled CMIP data using regional climate modeling by Coordinated Regional Climate Downscaling Experiment (CORDEX) is also available. The CORDEX-CMIP5 data for North America can be accessed here: https://na-cordex.org/index.html. The whole dataset can be accessed here: https://cordex.org/data-access/cordex-cmip5-data/bias-adjusted-rcm-data/. Note that no direct wildfire indicators are provided in the CORDEX data. Users will need to calculate these indicators using the available variables.
• Higher-resolution (25 km) CMIP6-like simulations (HighResMIP) is also available for some models. They can be accessed here. Note that same as CORDEX, HighResMIP data has no direct wildfire indicators.
• The North American Regional Climate Change Assessment Program also provides future projection simulations https://www.narccap.ucar.edu/data/access.html.

Fire risk data

• Spatial datasets of probabilistic wildfire risk components for the United States (270m) (3rd Edition)by USDA
• Fire hazard severity zone of California by FEMA
• Projected forest fire danger (2071-2100; RCP 4.5) in Europe by European Environment Agency

Other resources:

• National Interagency Fire Center (NIFC) provides comprehensive information on wildfire management and coordination among various agencies in the United States, including useful maps of the historical and current fires.
• U.S. Forest Service (USFS) offers extensive resources on wildfire prevention, suppression, and research, including detailed reports and data.
• Fire Information for Resource Management System (FIRMS) by National Aeronautics and Space Administration (NASA) uses satellite data to provide near real-time active fire data and tools for monitoring wildfires globally.
• National Oceanic and Atmospheric Administration (NOAA) Wildfire offers information on wildfire weather, satellite imagery, and forecasting tools to support wildfire management and research.
• Global Wildfire Information System (GWIS): A joint initiative by the European Commission and partners providing global wildfire information, including risk assessments, historical data, and monitoring tools.
  • Wildfire management in Latin American and Caribbean by GWIS
  • Pan-Europe wildfire risk assessment by EFFIS
• The Rangeland Analysis Platform is an online tool that visualizes and analyzes vegetation data (including annual forb and grass coverage) for the United States, including the Northwest.

Scientific literatures using their own datasets

Literature	Dataset introduction	Data link
Garroussi et al. 2024	Fire weather index calculated using CMIP 6 data	LINK
Sheehan et al. 2015	Fire variables such as burned area, fire interval simulated by a dynamic vegetation model
Abatzoglou and Brown et al. 2011	Energy Release Component and Fire Danger Index produced by statistical downscaling methods