Cooperative Institute for Research in Environmental Sciences
Sunday, June 3, 2018

Cranking Up the Volume on Wildfire

CIRES-led team uncovers series of wildfire triggers that culminated in the big burn of 2017

Fire burning foliage.
The Thomas fire burned >113,000 hectares from early December 2017 to late January 2018, making it the largest fire in California’s modern history.

Western wildfire seasons are worse when it’s dry and fuel-rich, and the chances of ignition are high—and all three factors were pushed to their limits last year, triggering one of the largest and costliest U.S. wildfire seasons in recent decades, according to a new paper. Climate change likely helped exacerbate fuels and dryness, the paper found, and people’s behavior contributed the sparks.

“Last year we saw a pile on of extreme events across large portions of the western U.S., the wettest winter, the hottest summer, and the driest fall—all helping to promote wildfires,” said Jennifer Balch, director of CIRES/CU Boulder’s Earth Lab and lead author on the study published today in Fire with INSTAAR, Columbia University, and University of Idaho coauthors.

The 2017 wildfire season cost the United States more than $18 billion in damages. That year, 71,000 wildfires scorched 10 million acres of land—destroying 12,000 homes, evacuating 200,000 people and claiming 66 lives. For comparison, 2016 saw only 5.4 million acres burned.

The research team sought to pinpoint the precursors that led to these fires, to support decision makers considering policies that might prevent or minimize future fire disasters. The study found that the three major “switches” affecting fire—fuel, aridity, and ignition—were either flipped on or kept on longer than expected last year.

It started with a wet winter. Increased precipitation early in 2017 fed the growth of fine grasses across the western United States—grasses that would later serve as fuel for fire. Summer and fall then swept in a wave of dry, arid conditions, baking the dense fields of grasses into dehydrated kindling.

With the fuel growth and aridity switches flipped on, the scene was set for the third switch: ignition. Nearly 90 percent of total wildfires last year were caused by people; previous work by Balch and her team has illuminated just how extensively humans exacerbate wildfire. Human activity triples the length of the average fire season.

Computer climate models project an increased risk of extreme wet winters in California, the paper notes, and a decrease in summer precipitation across the entire West Coast. Those models also tend to project a delay in the onset of fall rain and snow.

"We expect to see more fire seasons like we saw last year, and thus it is becoming increasingly critical that we strengthen our wildfire prediction and warning systems, support suppression and recovery efforts, and develop sustained policies that help us coexist with fire," said Megan Cattau, Earth Lab researcher and a coauthor on the study.

Although naturally occurring climate variability influences environmental conditions that affect the wildfire season, that variation is superimposed on an anthropogenically warmer world, so climate change is magnifying the effects of heat and precipitation extremes, Balch says.

The authors conclude by noting many ways that policy makers have already taken action to build better and burn better in the face of increasingly flammable landscapes; and they urge continued attention to policies that address the challenge of wildfire. 

“The 2018 wildfire season is already underway and here at home in the southern Rockies fuels are very dry,” said Balch. “It is forecasted that June will be a busy month in terms of wildfires due to severe drought and low snowpack.”


Headshot of Katie Weeman

Katie Weeman

Past Employee

Recent News