California has seen an uptick in wildfires, from Siskiyou County to San Diego.
Southern California has caught the brunt of the surge. Nearly a dozen fires have, together, consumed more than 26,000 acres of varied terrain in the region over the last week, in remote island chaparral as well as brushy foothills bordering neighborhoods. Six people have been injured and some 45,000 more remain under evacuation orders. At least one home has burned.
This level of activity may seem unusual for May, but experts say that, increasingly, that is no longer the case as climate change rolls back the start date of what’s traditionally been considered the peak fire season.
There are currently five fires of 1,000 acres or more burning in Southern California, which UCLA professor and hydroclimatologist Park Williams described as abnormal for this time of year but not unprecedented according to a dataset of past fires he maintains.
He pointed to a study suggesting that human-caused warming has advanced the onset of the fire season by six to 46 days across most of the state, primarily by drying out vegetation. “So the fact that the fire season is beginning now in Southern California is pretty predictable, given that it’s been really abnormally dry and warm.”
The region hasn’t seen much precipitation since December — the rest of the rainy season was mostly dry outside of some episodic showers, he said. Meanwhile, the Western U.S. as a whole experienced record-breaking heat in January through March, rapidly melting the mountain snowpack, he added.
Most of the fires burning in California right now ignited during an offshore wind event that engulfed much of the state, said Battalion Chief David Acuña of the Department of Forestry and Fire Protection. Although the winds weren’t as fierce as during the Santa Ana events sometimes seen in the fall, they combined with extremely dry fuels to create a dangerous situation, he said.
Swaths of the region are carpeted in grasses that each year grow and then die, creating what Acuña described as a patchwork of layers. “You can kind of imagine that all of Southern California is like a haystack right now, waiting for a single spark,” he said.
Humans are all too often the source of that spark — people start an estimated 95% of wildfires statewide, and in Southern California’s lower-elevation areas, that figure is believed to be even higher. The state’s largest fire of the year, the 16,942-acre Santa Rosa Island fire in Channel Islands National Park, is believed to have been ignited by a shipwrecked mariner who fired off flares to catch the attention of rescuers. The 1,698-acre Sandy fire in Simi Valley, which is responsible for the bulk of the evacuations, may have been started by a tractor driver who hit a rock and generated a spark, police said.
Human ignitions have actually declined significantly in Southern California over the last 30 years, likely because people have learned to be more careful and population increases have fragmented the landscape, Williams said.
Yet the region hasn’t seen a coinciding reduction in the amount of area burned by wildfires or the rate at which people are exposed to fire danger, he said. He attributed this to temperature increases linked to climate change, as well as a decline in precipitation, both of which prime plants to burn. He also noted that people continue to move into fire-prone wildland areas amid a statewide housing shortage.
Across California, 1,521 fires had burned 48,135 acres as of Wednesday, compared with a five-year average of 2,163 fires burning 23,867 acres at this point — significantly fewer fires but more area burned, Acuña pointed out. “What that tells me is, we have a lot more fuel on the ground that is lighting up more quickly and burning faster,” he said. “Combine that with hotter temperatures and more wind, and that’s how these fires are getting so big so fast.”
Climate change played a role in driving the abnormally warm temperatures that helped dry out fuels this spring, though it’s difficult to say to what extent without further research, said climate scientist Alex Hall of UCLA, who has found that global warming accounted for approximately 25% of the extreme vegetation dryness leading up to last year’s Los Angeles firestorms.
“Otherwise, I think the factors that led to this surprising explosion of fire in Southern California were due to a series of events that we’re familiar with from the historical record,” he said. Large fires in the spring typically coincide with an abnormally dry end to the wet season, and gusty winds are also known to raise fire risk, he said.
It’s unclear what the spike in activity portends for the rest of the fire season. Some forecasters are predicting that Northern California will see an above-normal incidence of significant fires due to the dryness of the vegetation, but the picture for Southern California is less clear.
The region typically experiences its most damaging fires when Santa Ana winds blow in the fall, and it’s not yet known how prevalent or strong those will be, or whether winter rains may reach the area first.
Still, Hall said, “because of the dry conditions at the end of the wet season here this year and the warm temperatures, we’re not starting out in a good place.”
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