Here is a lengthy and interesting piece in the LA Times :
The California Department of Forestry and Fire Protection did not respond to repeated interview requests for this story. But the widespread shut-offs underscore the huge — and often overlooked — role that human-related ignitions play in California wildfire.
It doesn’t matter how dry the vegetation, how fierce the winds or how high the temperature; if there is no ignition, there is no wildfire.
Outside of the Sierra Nevada and the state’s northernmost tier, there is little lightning, nature’s ignition source.
That means that, in much of California, more than 90% of the wildfires are started by people or their equipment. In coastal counties from Sonoma to San Diego, almost all the starts are human related.
In 2018, the worst wildfire year in the state’s record, 1.8 million acres burned in California. Lightning torched only 117,107 acres, according to federal statistics.
Of the known causes of the state’s 20 most destructive wildfires, all are human-related. Half were started by power line or electrical problems, including the two most devastating, the Camp fire, which incinerated 18,804 buildings, and the 2017 Tubbs fire, which killed 22 people and destroyed 5,636 structures.
Other causes of the top destructive blazes include sparks from driving a trailer on the rim of a flat tire (the 2018 Carr fire in Shasta County); a hunter’s small signal fires (the 2003 Cedar fire in San Diego County); and arson (the 2003 Old fire in San Bernardino County).
Human starts aren’t just a California problem. Researchers who analyzed two decades of U.S. records found that, from 1992 to 2012, human activity was responsible for 84% of the wildfires and 44% of the area burned nationally.
The scientists also concluded that people have dramatically expanded the fire season — extending it by far more than a warming climate — because they start fires virtually year-round.
“We’ve forgotten the importance of human ignitions in the mix of this,” said Jennifer Balch, lead author of the 2017 paper, which was published in the Proceedings of the National Academy of Sciences.
“I’m not saying that climate change is not important,” added Balch, who directs the Earth Lab at the University of Colorado-Boulder.
“I’m saying we have a confluence of climate change setting the stage for warmer and drier conditions — and people are providing the ignitions for those large blazes,” she explained. “The convergence and timing is really unfortunate.”
The one hopeful aspect, she said, is that “we can actually do something about it.”
Clearly something is going on,” said Keeley, who offered two possible explanations: The state’s power distribution infrastructure is aging, and the electrical grid has expanded as development pushes farther into wildlands.
Widespread power shutdowns have not been in play long enough to ascertain if they are effective, he said.
Still, Keeley said the 2019 fire season challenges the notion that the horrific wildfire toll of recent years is the “new normal” wrought by climate change.
“People have to recognize there is a lot of serendipity. It has to be the match-up of a number of things” to create catastrophic fires, he added.
One critical match-up is timing.
It is not the number of ignitions that drives wildfire destruction. There were 8,315 fires in California in 2019 — a couple of hundred more than in the devastating 2018 season, according to the National Interagency Fire Center.
It is the conditions under which ignitions occur that matter the most. If it’s a red flag day with single-digit humidity and howling Santa Ana or Diablo winds, chances are greater that a few sparks can quickly explode into a freeway-hopping conflagration that sets entire communities ablaze.