The speed and ferocity of the wildfires raging through Northern California's wine country have caught many residents off guard and left state officials scrambling to contain the flames.
But for fire researchers, these devastating blazes are part of a much larger pattern unfolding across the Western United States. So far this year, fires in the U.S. have consumed more than 8.5 million acres — an area bigger than the state of Maryland.
"We're definitely pushing one of the largest fire years this decade," says Jennifer Balch, a fire ecologist at the University of Colorado, Boulder.
The cause is hot, dry conditions nationwide. Heat records have been broken this year in California, Oregon and Montana. Globally, 2017 is among the hottest years on record, thanks in part to human-induced climate change.
Wildfires are natural phenomena, and linking any one fire to climate change is difficult if not impossible. Nevertheless, "there is a link between a warmer, drier climate and wildfires," Balch says. For example, today's fire season is three months longer than it was in the 1970s, she says. Annually, there are far more large fires nationwide than there used to be.
"It doesn't take a rocket scientist to figure out that forests burn when it's warm and dry, and we've seen more of those years recently," says John Abatzoglou of the University of Idaho.
This year has been "pretty impressive," he says. "I'm in Northern Idaho, and we had smoke coming from British Columbia and Oregon and California."
In the case of the wine country blazes in Napa and Sonoma, Abatzoglou says a sequence of events set up the wildfires. A wet spring caused the hills to grow thick with grasses and shrubs. That foliage then died and dried out over the hottest summer in California history.
Then came unusually strong fall winds, which were not climate-related. The winds caused small fires to grow extremely quickly. "Everybody from firefighters down to homeowners has commented on just how incredibly fast the fires were moving," says Max Moritz, a researcher at the University of California, Santa Barbara. "That's really a wind-related phenomenon."
There are things that can be done to reduce the fire threat. Earlier this year, Interior Secretary Ryan Zinke issued a call for more aggressive actions to suppress fires. He encouraged land managers nationwide to clear potential fuel sources, such as dead trees, and expand the clearings along roads to create stronger firebreaks.
But Balch and others say these actions are only part of the solution. As fires become more common — and humans build farther into natural landscapes prone to fire — more must be done to protect communities.
California has been leading the way in developing regulations to protect against fires, Moritz says. The state fire agency, Cal Fire, has produced fire hazard maps. In high-risk zones, there are building requirements such as fire-resistant roofs and window screens that can block embers from floating into a home.
But Moritz points out that the hazard maps exclude urban areas. There, local municipalities have their own building codes, which can be less stringent than Cal Fire's.
He says that more urban areas might need to incorporate fire planning into their communities. That could mean building homes differently or improving evacuation and shelter options for residents. "Almost annually, we're seeing large, large numbers of homes being lost in big fire events," Moritz says. "Maybe we need to update our perspective."
Balch says that while the big picture of drought and climate provides some answers about the situation in Napa, the details of individual fires matter. That's why after the latest wildfires in California burn out, she and other researchers will begin to study exactly what happened.
"There are lots of really important questions that we as a scientific community have to answer," she says. "Particularly when homes are burned and people's lives are threatened or lost."