“For the last century we fought fire, and we did pretty well at it across all of the Western United States,” Dr. Williams said. “And every time we fought a fire successfully, that means that a bunch of stuff that would have burned didn’t burn. And so over the last hundred years we’ve had an accumulation of plants in a lot of areas.
“And so in a lot of California now when fires start, those fires are burning through places that have a lot more plants to burn than they would have if we had been allowing fires to burn for the last hundred years.”
In recent years, the United States Forest Service has been trying to rectify the previous practice through the use of prescribed or “controlled” burns.
The Santa Ana winds
The second stage of this year’s fire season is yet to come.
Each fall, strong gusts known as the Santa Ana winds bring dry air from the Great Basin area of the West into Southern California, said Fengpeng Sun, an assistant professor in the department of geosciences at the University of Missouri-Kansas City.
Dr. Sun is a co-author of a 2015 study that suggests that California has two distinct fire seasons. One, which runs from June through September and is driven by a combination of warmer and drier weather, is the Western fire season that most people think of. Those wildfires tend to be more inland, in higher-elevation forests.
But Dr. Sun and his co-authors also identified a second fire season that runs from October through April and is driven by the Santa Ana winds. Those fires tend to spread three times faster and burn closer to urban areas, and they were responsible for 80 percent of the economic losses over two decades beginning in 1990.
It’s not just that the Santa Ana winds dry out vegetation; they also move embers around, spreading fires.
Which brings us back to climate change.
Ultimately, determining the links between any individual fire and climate change takes time, and analysis from the evolving discipline of attribution science. But the effects of the greenhouse gases humans produce underlie everything that occurs in the atmosphere, and the tendency of climate change to make dry places more dry over time is a warning to the West of a fiery future.
This article originally appeared in 2018. It was updated in August 2020.