As temperatures climb across the West and as a sprawling Bay Area expands development into increasingly rural reaches, Northern California is becoming more akin to Southern California, where warm weather and people staking trophy homes along far-flung cliffs and canyons have set the stage for chronic burning, fire experts say.
“I can’t imagine how there isn’t going to be more of this in the future,” said Hugh Safford, an ecologist for the U.S. Forest Service’s Pacific Southwest Region. “It’s shocking what’s happened, but it really isn’t necessarily all that surprising.”
In the past few years, the north state’s coastal mountains have witnessed several devastating burns, much in line with what the southern coast has long endured. In 2015, the Valley Fire that spread into Lake, Sonoma and Napa counties destroyed nearly 1,300 homes and killed four people, and the following year a blaze wiped out the heart of the Lake County town of Lower Lake.
The most destructive of this week’s wildfires are within an hour’s drive south of Lower Lake, but they swept into areas much more populated, such as the north edge of Santa Rosa, intensifying the impact.
“That part of the state over the past four years ... has had an endless series of unrelenting fires,” Safford said. “It’s typical of the coast ranges, when you get to Santa Barbara and south, which are dry and hence more flammable. But this is really a new thing here. I think that Lake County may be the next frontier of Southern California as it moves north.”
While fall has always been the most perilous season for Northern California wildfires, as offshore winds pick up and the trees and shrubs reach their driest points after the warm summer months, a number of the underlying forces have changed in the past decade or two.
The most obvious is temperature, which has risen globally as a result of human-induced greenhouse gas emissions. This summer marked California’s hottest in recorded history. San Francisco reached an all-time high of 106 degrees in September, continuing a trajectory that’s put the Bay Area more on par with balmier Southern California.
The milder weather means that vegetation is dryer and more combustible and that the fire season runs longer, perhaps eventually becoming a year-round affair as it is in Southern California.
“As long as you have stuff to burn, warming temperatures increase the likelihood that stuff is going to burn,” said Park Williams, a bioclimatologist and research professor at Columbia University’s Lamont-Doherty Earth Observatory in New York. “Climate is certainly driving the trends that we’re seeing in fire across the West.”
A study published last year by Williams suggests that as much as half the burning of forest land in Western states since the 1980s is due to global warming.
Research also shows that extremes of weather both wet and dry — another product of climate change — are pushing more powerful blazes. Climate experts point with alarm to the way this year’s extraordinarily rainy winter in California, which created a bumper crop of brush and grass, gave way swiftly to record heat that dried out the wildlands and provided copious fuel to burn.
“This is the recipe for bigger fires,” Williams said. “Most models agree that the frequency of extremely wet years will increase, and that happens at the same time that all models show things getting warmer.”
The same models explain the deadly string of hurricanes that battered parts of the U.S. and the Caribbean over the past few months. And they may explain recent landslides and drought in Africa, and threatening tsunamis in Central America.
West Coast scientists are also investigating whether the warming planet is intensifying the hot offshore winds that have driven this week’s Wine Country fires, commonly called Diablo winds.
At the same time, researchers are looking into whether climate change is tied to warmer evening temperatures, which have allowed fires like the ones in Napa and Sonoma counties to burn overnight rather than begin to cool. The worst damage in Sonoma County occurred between midnight and dawn on Monday.
While climate has created a playing field more conducive to furious and frequent fires, the root cause of the burns remains, almost exclusively, human failing. Northern California’s coastal mountains don’t see much lightning, and before the hills were settled, fire was relatively uncommon here. Today, there’s no shortage of ignition sources, whether downed power lines, automobile tailpipes or cigarette butts.
“People want to live out in the woods, and this is always a real and present danger,” said Safford of the Forest Service. “These fires should probably be a wake-up call to think more about human habitation and how we deal with that.”
The growth of fires will likely put increasing pressure on state and federal firefighting budgets. Just three months into the current fiscal year, the California Department of Forestry and Fire Protection had spent $258 million of its roughly $430 million annual emergency fund — and that was before the Wine Country fires broke out.
“This week’s fires alone are going to chew up quite a bit of what is left,” said Cal Fire spokeswoman Lynne Tolmachoff. “And we’re not done with fire season. We don’t have any precipitation showing up in our forecasts. And then there’s the fires in May and June next year.”
While it’s still early in the budget year, Cal Fire’s outlay is nearly on pace with the record $547 million expended in 2015-16, an amount that required the state to tap other funding streams as well as federal aid. The amount of emergency money spent annually by Cal Fire in the past five years is more than double what it was a decade ago.
Through Sunday, before wide swaths of Northern California turned into a disaster zone, wildfires had blackened about 850,000 acres across the state, nearly 70 percent above the five-year average for the date.
Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander
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