Green trees and low shrubs in the middle of a forest burn in a fire. The fire burns primarily in the center of the image with a few smaller fires seen in the background and around the edges of the image. The entire image is viewed through a haze of smoke.
Wildfire burns trees and shrubs in the 2013 Rim Fire in Yosemite National Park. Credit: Jon Keeley/USGS, Public Domain

Throughout the 2000s, fires increased in number, size, and frequency across the contiguous United States compared with the previous 2 decades, new research has shown. Extreme fires increased primarily in the western and Great Plains regions, while moderate and small fires worsened across the entire country. These fire pattern changes, which threaten human and ecosystem health, are attributed to a combination of climate change impacts and human expansion into new and burnable land.

“Every year we spend billions of dollars fighting fires, and we lose homes, infrastructures, and lives.”

“Every year we spend billions of dollars fighting fires, and we lose homes, infrastructures, and lives,” said Virginia Iglesias, a climate scientist at the University of Colorado Boulder’s Earth Lab and lead author of the new study. “And then there’s smoke, which affects the well-being of millions of people. Because the impacts of fires are increasing, there’s this idea that fires are also getting worse.” Recent work has shown that development along the wildland-urban interface is exposing more people to natural hazards and contributing to the increases in loss, “and now we wanted to tell the other side of the story. We wanted to test whether, in addition to an increase in exposure due to development, fires were also getting worse.”

Bigger Fires and More of Them

The researchers analyzed more than 28,000 fires that took place from 1984 to 2018 across the contiguous United States. They gathered data from the Monitoring Trends in Burn Severity data set, which combines Landsat data with federal and state fire reports. They split the data into two time periods, 1984–1999 and 2005–2018, and into West, Great Plains, and East regions to examine how fire size and frequency have shifted over time in different parts of the country.

“We found that all regions see more fires since 2005 than in the past,” Iglesias said. “In the West and East, there are twice as many fires as before, and in the Great Plains there are 4 times as many fires as before. We saw that fires doubled in size in the West and increased by 150% in the Great Plains.”

Two maps of the contiguous United States show the spatial distribution of fires during a past time interval (left) and a more recent time interval (right). In the past, there were many smaller fires concentrated in the western, southwestern, and Gulf Coast states, with a few extreme fires dotted mostly around the Pacific Northwest and along the Atlantic Coast. More recently, small fires have become more frequent in the western United States, Great Plains, along Appalachia, and along the Atlantic Coast. Extreme fires have also become more frequent but only in the western and central United States.
These maps show the spatial distribution of fires in the United States in 1984–1999 and 2005–2018. Small yellow dots represent small fires, large orange dots represent fires considered large by 1984–1999 standards, and large red dots represent fires considered large by 2005–2018 standards. Credit: Iglesias et al., 2022,, CC BY-NC 4.0

The team found that in recent years, the total land area burned increased fourfold in the West and more than sevenfold in the Great Plains. In the East, fires didn’t change significantly in size or in total area burned. These results were published in Science Advances on 16 March.

“We know that the social side is getting worse because of development. We’re exposing more [land],” Iglesias said. “Now we’re showing that the physical side, the hazard itself, is also changing.”

Peter Teensma, a senior policy and science adviser with the U.S. Department of the Interior’s Office of Wildland Fire, said in a statement to Eos, “The study was a more detailed statistical and geospatial analysis of wildfires…than our office has conducted, but the results are generally consistent with our observations.” Teensma added that research like this helps provide a sound scientific basis for the Interior department’s wildland fire management strategy and that ongoing climate and fire research will provide further scientific footing and direction for wildfire management.

Cascading Consequences

Although some ecosystems benefit from periodic wildfires, much of the new land that has burned or is likely to burn in the future includes ecosystems that have not adapted to frequent fires and are not as quick to recover. Some research already has shown that “reestablishment is compromised in some areas after a fire because climate has already changed, so seedlings can’t survive,” Iglesias said. A slow-to-recover burnt landscape might lead to polluted water sources, erosion or landslides, and health impacts from airborne ash. “The effects of fires cascade down the ecosystem, make it all the way to our societies, and can have very unexpected consequences,” Iglesias added.

Despite repeated calls for climate mitigation and better fire prevention, none of these trends is likely to abate in the future without significant action.

The researchers suggested that the new fire patterns in the early 2000s are likely due to changes in three underlying factors: drought, ignitions, and fuel. Changes in all three can be traced back to humans. Anthropogenic climate change has increased the severity, extent, and duration of droughts in the United States over recent years, turning more and more land arid and at risk of catching fire. Too, recent studies have revealed that humans ignite 84% of fires in the United States through accident, neglect, or arson. And cities increasingly are developing outward into undeveloped, high-fire-risk land, bringing the primary ignition source (people) into contact with new burnable fuel. Despite repeated calls for climate mitigation and better fire prevention, none of these trends is likely to abate in the future without significant action, Iglesias speculated.

Teensma said the federal government “is working to adapt to the trends this study identified, including large wildfires occurring across geographic areas, wildfires recurring more frequently than the natural fire regime would support, and the impact of nonnative species on changing wildfire patterns.” Those changes include transitioning to a year-round wildland fire workforce to address the increasing demand posed by the new fire patterns.

Teensma added that the Infrastructure Investment and Jobs Act, which was signed into law in November 2021, will provide a historic increase in wildland fire management funding that will expand the Interior department’s efforts to reduce wildfire risk, restore ecosystems, prepare for and respond to harmful wildfires, and support postfire recovery, including in communities that historically have been overlooked.

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Citation: Cartier, K. M. S. (2022), U.S. fires quadrupled in size, tripled in frequency in 20 yearsEos, 103, Published on 08 April 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
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