So far this year, Southern California has spared massive wildfires that devastated areas of Northern California, but the days of the region’s reckoning are coming.
“Wildfire season really comes to a head in Southern California in October,” said Dan Keon, a climate researcher at the Scripps Institution of Oceanography. “A lot of other areas in California are more summer-focused.”
The severity of the region’s drought, Santa Ana winds, and the potential for a La Nia system that could limit fall and winter rainfall are conspiring to increase Southern California’s wildfire risk next month, Cian said Monday, Said during a dry webinar on Sept. 27. The online gathering was hosted by the National Integrated Drought Information System, which is led by NOAA, the National Oceanic and Atmospheric Administration.
Sian said that in Southern California, 93% of acres burned from 1948 to 2018 occurred before the season’s first rain of an inch or more. And the average date of that first rain is November 10.
At the same time, the dominant season of hot, dry, fierce Santa Ana winds begins in October and lasts through February.
“All the biggest (southern California) fires are wind-driven, including in Santa Anas,” Sian said.
“If we don’t get rain, and we get Santa Anas, we’re at more risk.”
The western United States is in its second year of drought. Most of California, 88%, is experiencing extreme or exceptional drought, and parts of the Sierra Nevada and northern California are experiencing the worst drought on record, said UC Merced climate researcher John Abatzoglu.
Last winter was California’s third driest since 1895, and the past 90 days have been the warmest in at least 125 years. The two conditions are related.
“You get dry soil and you get high temperatures,” Abatzoglu said.
While forest fires have scorched slightly less area across the state than last year’s record-breaking fires, the trend of more fires and more severe fires continues. Six of the seven fires burning the most land in California have occurred in the past two years and the second largest fire on record – the Dixie fire – began in July and is still burning. Two other still-burning wildfires have burned more than 200,000 acres, while a third stood at 198,000 acres as of Monday.
Noting Southern California’s vulnerability, Abatzoglu said that thanks to warmer-than-normal waters in the North Pacific, 70% to 80% of the La Nia system is formed.
“La Nia usually translates to dry years in the southwest,” he said. “We’re looking at back-to-back La Nia years.”
Drought is also affecting water supply. While Southern California’s reservoirs are in good condition so far, officials have called for water use to be reduced in preparation for the prospect of another winter with less rain. However, most Northern California reservoirs are “substantially low,” according to Abtzoglu.
The biggest early drought impact on water supplies is the reduction of surface runoff from storms, which requires water agencies to tap into more groundwater. In a typical year, groundwater accounts for 40% of the water supply, according to Steven Springhorn of the California Department of Water Resources.
But this rises to 60% during droughts – and with that effect there is less water available to recharge groundwater, which is being felt.
Of the 305,000 wells monitored by Springhorn’s department, more than 700 are dry. Springhorn said 64% of the 3,200 monitored wells are below normal levels — including several at historic lows.
The ultimate solution, of course, is more rain.
“We are hoping for the best, but planning for the worst,” he said.