Rising summer temperatures could lead to an exponential increase in the number of wildfires and acres burned in the Sierra Nevada in California, researchers have found.
The study, published Wednesday in the journal Science Advances, found that there’s a 19% to 26% jump in wildfire risk for each degree of summer temperature increase in the Sierra Nevada. Given that connection, the number of wildfires in the region could rise by as much as 83% by the 2040s, and the area burned could climb by 92%, according to the study.
Aurora Gutierrez, an environment and climate researcher at the University of California, Irvine, said that as planet-warming fossil fuel emissions rise, the number of fires and charred areas will only worsen.
“Fires are very sensitive to small changes in temperature,” Gutierrez, the lead author on the report, told CNN. “And so there could be a lot of potential risks with that, when we’re talking about climate change and future scenarios in that region.”
The researchers analyzed 441 fires that burned at least 100 acres in the mountain range between 2001 and 2020 to quantify the relationship between fire occurrence and daily temperatures. During that time, most of the fires were sparked from June to September, and a total area of more than 2.5 million acres burned.
The Sierra Nevada is home to the giant sequoias, the largest trees in the world. The past two years of wildfires in California have taken a massive toll on the trees, which can live for thousands of years. The National Park Service estimated 10% to 14% of the world’s giant sequoias — 7,500 to 10,600 trees — were destroyed the Castle Fire in 2020.
The 2021 fire season was similarly devastating: the Caldor and Dixie fires alone torched nearly 1.2 million acres of the Sierra Nevada, according to Cal Fire. Those fires destroyed more than 2,300 structures.
Gutierrez said lightning-sparked wildfires have been historically widespread across the Sierra Nevada, but fire management by Indigenous peoples made it less severe. That balance changed with modern fire suppression policies, land use changes, population growth and warming temperatures.
“The consequences of suppressing fires for so long was that we had a very big overgrowth of fuel, of vegetation in that region,” Gutierrez said.
The research follows previous studies that have often relied on monthly or annual burned area data when considering the impacts of the climate crisis on wildfire trends in the West, Gutierrez said.
Daniel Swain, a climate scientist at UCLA, who was not involved with the study, said the latest research is a vital addition to a growing body of science that links wildfires to climate change.
“The interesting piece here is that the effect of daily summer temperatures on fire appears to be non-linear, meaning that each additional degree of warming has a greater influence than the last,” Swain told CNN. “This is in line with other work suggesting that wildfire size and severity is increasing in a non-linear fashion in response to the increasing ‘vapor pressure deficit’ — a measure of atmospheric ‘thirstiness’ that is directly related to both humidity and temperature.”
Swain says that as a result of this non-linearity, “the climate-fire connection will continue to amplify and accelerate with each additional degree of local warming, which will challenge societal efforts to keep pace with the changing character of wildfire in the 21st century.”
The findings reflect what global scientists concluded in August: That with every fraction of a degree of warming, the effects of the climate crisis around the world from floods to drought are set to worsen.
And after a summer of landscape-altering wildfires, unrelenting drought and deadly heat waves in the Western US, Gutierrez said the region should adapt and prepare for more climate change-fueled disasters in the near term.
“The potential for fires to grow will increase exponentially into the future,” she said. “With climate change, it’s an amplifying cycle. It’s just a matter of considering how we’re going into the future by how we manage the land.”
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