California’s Coastal Range Fires Are Getting Significantly Worse Every Decade, Experts Say

Sherree Brose has lived in the hills west of Vacaville for a quarter of a century. Last month a lightning sparked fire surrounded her small acreage. That fire, the LNU Lightning Complex, although nearly contained, spans across five counties and has burned over 360,000 acres. 

After she evacuated her home — which was built in 1846 and survived three previous fires — her son-in-law went back in with a water truck as the flames surrounded her property.

“My house is on the other side of that smoke and … he couldn’t save my pump house, but he saved my old shed and house,” the retiree said as she fought through tears. “It was fast and furious. I know that other people in the area, their houses are gone.” 

Large-scale wildfires in the Northern part of the coastal range like the LNU Lightning Complex have been increasing at about 10% per decade since 1984 due to climate trends that make it easy for wildfires to spark. That’s according to a new UC Davis study analyzing the coastal range through satellite imagery from 1984 to 2017.

Yufang Jin, co-leading author of the study and associate professor in the UC Davis Department of Land, Air and Water Resources, said the increases “emphasized the impact of warming temperatures on the severity of burns.”

The researchers found a correlation between drought and acres burned. The 2012-2016 drought about quadrupled the area that burned severely when compared to the 1987-1992 drought, which was cooler. The study area includes coastal foothills and mountains surrounded by Central Valley lowlands to the east from Lake Berryessa stretching north to the Klamath Mountains. 

“The fire size has been increasing significantly — the mean fire size almost doubled if you compare the recent drought period with previous relatively cooler drought —  and the severity of burns also were amplified,” said Jin.

Even though the entire study area is prone to fire, they found that during dry years the northwest and southern parts of the study areas are at risk of high-severity fires — which usually means nearly all the vegetation is killed and loss of nutrients in soil. Their data analysis shows that from 1984 to 2017 about 36% of all fires burned at high severity. That number decreased to 20% during wet years. 

They also found that higher temperatures, like this year’s August heat wave, make fires worse. 

“This trend of increasing temperatures and also the dryness might lead to more intense, higher fire risk,” said lead author Yuhan Huang, a graduate student researcher at UC Davis.

The new research about fire severity in the coastal range is important in light of recent findings that the number of perfect fall days for a wildfire to start — which is when some of the largest fires in the state have ignited in recent history — has jumped from four to 12 since 1979. The increased fire danger is a result of less rain and warmer temperatures.

A group of scientists from Stanford, UCLA and UC Merced conducted the study. Like the UC Davis study, it points to increased fire danger as a result of less rain and warmer temperatures. These additional days result from just a one degree rise in global temperatures, says study co-author and Stanford climate scientist Noah Diffenbaugh.

“Another degree of global warming on top of that, and we can be confident it will increase the occurrence of extreme wildfire weather further,” he said. “The trajectory we've been on will likely lead to greater than three degrees, and potentially four or five degrees.”

With just one degree, California is already experiencing some of the worst wildfires in history. That’s why Jin says it’s important that state, federal and local agencies take fuel management seriously — as well as well reduce greenhouse gas emissions, which warm the atmosphere. 

“We expect future fire risks to continue at the current pace, because a lot of our climate models projections have the same conclusions,”Jin explained. “We'll be seeing a warmer climate in the future.”