More than 4400 square kilometres have burned across California in the past 10 days, as firefighters continue to battle some of the state’s worst wildfires, which have left seven people dead, and more than 100,000 evacuated. More than two dozen major fires are still raging, including .
żěè¶ĚĘÓƵs say climate change helped set the stage for the hot and dry conditions that enabled more than 600 fires started by lightning on 15 August to expand so rapidly. Last Friday, the extent of the conflagration doubled in a day. There was then less lightning over the weekend than had been feared, but concerns remain over damage to millennia-old redwood trees. The fires followed a heatwave that caused blackouts, with , the highest temperature ever recorded on Earth, pending verification.
“Exceptionally hot weather over the past two weeks certainly played a proximal role in drying out vegetation to this extreme degree,” says Daniel Swain at the University of California, Los Angeles. But the drying of fuel also started earlier, he notes, with heatwaves in the spring and last winter being very dry in northern California.
Advertisement
There are several unusual aspects to the current fires, even for a region used to intense fire. They expanded dramatically in the absence of the usual driver for large and fast-moving fires in the state: powerful, dry winds.
“That makes the enormous acreage burned in such a short time all the more astonishing, since they’re essentially spreading on accord of their own intensity,” says Swain. The ignition by dry lightning – thunderstorms without rain – is also rare for the region, says Stephen Pyne at Arizona State University.
Researchers say climate change is almost certainly linked to the conditions that have made the fires so severe.
“It’s hard to believe that climate change isn’t contributing,” says Pyne, who points out this is the fourth major fire year in a row, when historically California saw 7 to 12 years between big fire seasons. The main mechanism is hotter temperatures drying out vegetation in and . “It is abundantly clear that climate change is increasing the likelihood and intensity of heatwaves in California,” says Swain.
The vapour-pressure deficit (VPD), the difference between moisture in the air and the amount at which the air becomes saturated with water, is , says Thomas Smith at the London School of Economics. “Higher VPDs ,” he says. The fires have , known as pyroCbs, as well as . There are fears that even fire-resistant redwoods may be killed off, but researchers say it is too early to say how the trees have fared.
Although the California Department of Forestry and Fire Protection has 14,000 people fighting the fires, observers say it is impossible to have enough crew to stop fires this big and dispersed. “California would have to become the fire equivalent of a police state,” says Pyne.
In the short term, reducing the amount of fuel by thinning vegetation and forests is considered a key mitigation against future fires. Authorities last week . With climate change locked in for the next three decades, longer term the answer is to reduce carbon emissions, says Smith.
