The map shows where California wildfires have become most explosive
Climate change has made California’s wildfires more explosive, increasing the number of days with extreme growth by 25%, according to a study by scientists at San Jose State University, UC Berkeley and other California research institutions.
While previous studies have looked at how climate change affects wildfire activity over entire years, the new work provides insight into the daily behavior of fires.
The researchers used machine learning methods to analyze wildfires in California from 2003 to 2020 and identified details about the terrain, weather and fuel types associated with fire growth over 10,000 acres in a single day.
To explain how climate warming affects the extreme growth of fires, the researchers ran machine learning models using temperatures representative of the pre-industrial era — before human activity had significant impacts on global climate — while keeping other weather variables the same.
This map shows how some of the state’s most destructive wildfires are affected by climate change. The 2020 North Complex fires, which destroyed about 2,300 structures and killed 15 people, saw days increase by 40% with explosive growth as a result of climate change. But the 2018 Carr Fire, which destroyed about 1,600 structures and caused eight deaths, saw only a 6% increase.
The 2020 CZU Lightning Complex fires, which destroyed about 1,500 structures and caused one death, had an increased risk of severe growth of 24%.
The authors suggest that these differences stem from the fact that the warmer the atmosphere, the thirstier it is.
“It’s basically better at absorbing moisture from fuel,” said study co-author Patrick Brown, a climate scientist at the Interdisciplinary Wildfire Research Center at San Jose State University, the Breakthrough Institute, and Johns Hopkins University.
The analyzes revealed critical fuel moisture thresholds that lead to intense wildfire activity.
“When (global) warming pushes you from the wet side to the dry side of those (thresholds), it dramatically increases the risk of overgrowth,” Brown said.
For example, the North Complex fires occurred under conditions overlapping critical thresholds, so human-induced global warming tipped the balance. In contrast, the Carr Fire occurred under extremely dry conditions and global warming had little effect on the risk of explosive wildfire growth, which was already high under pre-industrial conditions.
CZU Lightning Complex fires destroy a garage and trailer in Boulder Creek’s Trade Winds neighborhood on August 22, 2020.
Sarah Gobits/Special on 2020The researchers used a similar approach to study how projected temperature increases for a range of greenhouse gas emissions scenarios would affect the extreme growth of wildfires.
While California saw 380 incidents of extreme daily wildfire growth from 2003 to 2020, that number rose to 459 when considering average projected 2081-2100 temperatures under a low-emissions scenario. This number jumped to 786 below temperatures in the very high emissions scenario.
“There is still a lot we can unpack to get a better understanding,” said Mike Flannigan, a professor of wildland fire at Thompson Rivers University, who was not involved in the research but was a reviewer of the study. “But the bottom line here is we’re seeing temperatures rise, we’re seeing more fires, and we’re going to see more fires in the future as temperatures continue to rise.”
Future areas of research could be the influence of other weather factors and human activity on the extreme growth of wildfires, said Janine Baijnath Rodino, UCLA’s director of meteorology and adjunct assistant professor of atmospheric and oceanic sciences, who was not involved in the new work. e-mail.
“This is a great step toward discovering more about how extreme events across California will impact us as our climate changes,” said Baijnath Rodino, of the study.
Researchers are now delving deeper into some of these areas, using a more sophisticated approach to examine how vegetation influences extreme fire growth. Preliminary results suggest that reducing hazardous fuels could offset the impact of climate change on fire danger.
“You have to focus on more direct, realistic solutions in the near term to do anything within the timescale we’re interested in,” such as mechanical thinning and prescribed burning, Brown said.
Reach Jack Lee: jack.lee@sfchronicle.com
