As deadly wildfires sweep through California's wine country, fire management experts are blaming their violent speed on the powerful Diablo winds. But the conditions that made the fires so destructive arose from this summer's record-breaking heat—a kind that experts say will continue to fuel fires across much of the West as the planet warms.
The state has seen more than 11,200 fires flare up so far this year, putting it on track to outpace the number that hit the state in 2015, which was the country's worst fire season on record, based on acres burned.
The fires had an especially ripe mix of fuel that made them explosive.
"The long-term drought is over, but there's still the legacy of that drought in terms of stressed forests. And on top of that we had a wet winter, which meant that the grasses and brush grew like crazy this spring," said Daniel Swain, a climate scientist at UCLA.
Then, the state experienced its hottest summer on record, with a record heat wave in late August and September that dried vegetation to a crisp. "California summers are always warm and dry, but this one had a particularly warming and drying effect," Swain said. "And we know there's a long-term trend toward warmer and hotter summers."
Already this year, 8.5 million acres have burned across the United States, not including the ongoing California fires. At least 115,000 acres have burned in the wine country fires, and several thousand more are ablaze in Southern California where the Santa Ana winds are fanning flames.
According to an analysis of NASA satellite data by the World Resources Institute's Global Forest Watch Fires, California has experienced 11,273 fire alerts—where satellites detect the heat signatures of fires—as of September. That number was 10,177 in September of 2015.
"It's following very closely with what happened in 2015," said Susan Minnemeyer, a mapping and data manager at WRI. "While 2017 is not a record year across the U.S., in California it is."
Across the nation, wildfires burned more acres in 2015 than any year in modern record keeping, surpassing 10 million acres for the first time. Despite the high number of fires across the West, it's unlikely that 2017 will catch up to that figure. (This year, however, has broken at least one wildfire-related record: The government has spent more than $2 billion fighting fires, making it the most expensive ever.)