Unprecedented drought, heat mark start of fire season for Southern California

So far this year, Southern California has been spared the massive wildfires devastating swaths of Northern California, but the region’s days of reckoning are approaching.

“The wildfire season really comes to a head in Southern California in October,” said Dan Cayan, a climate researcher at Scripps Institution of Oceanography. “A lot of other areas in California are more summer-centric.”

The severity of the region’s drought, Santa Ana winds, and the likelihood of a La Nina system that could limit fall and winter rain, are conspiring to heighten the risk of Southern California wildfires next month, said Cayan during a drought webinar Monday, Sept. 27. The online gathering was hosted by the National Integrate Drought Information System, which is led by NOAA, the National Oceanic and Atmospheric Administration.

In Southern California, 93% of the acres burned from 1948 to 2018 occurred before the season’s first rainfall of a third of an inch or more, Cayan said. And the median date for that first rain is Nov. 10.

At the same time, the prime season for hot, dry, fierce Santa Ana winds begins in October and lasts through February.

“All of the very largest (Southern California) fires are wind driven, involving Santa Anas,” Cayan said.

“If we don’t get rains, and we do get Santa Anas, we get more risk.”

Records broken

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 John  Abatzoglou, a UC Merced climate researcher.

Last winter was California’s third driest since 1895, and the past 90 days have been the hottest in at least 125 years. The two conditions are related.

“You get drier soils and you get higher temperatures,” Abatzoglou said.

While wildfires have scorched slightly less acreage statewide than last year’s record-breaking blazes, the trend of more fires, and more extreme fires, continues. Of the seven fires to burn the most land in California, six have come in the last two years and the second largest blaze on record — the Dixie fire — started in July and is still burning. Two other still burning wildfires have torched more than 200,000 acres, while a third was at 198,000 acres as of Monday.

With attention turning to Southern California’s vulnerability, Abatzoglou said there’s a 70% to 80% chance of a La Nina system forming, thanks to cooler-than-usual waters in the Pacific.

“La Nina usually translates to dry years in the Southwest,” he said. “We’re looking at back-to-back La Nina years.”

Water supplies

The drought is also having an impact on water supplies. While Southern California’s reservoirs are in good shape so far, officials have called for reducing water usage in preparation for the possibility of another winter with little rain. Most Northern California reservoirs, however, are “quite low,” acccording to Abatzoglou.

The biggest initial drought impact on water supplies is the lack of surface runoff from storms, requiring water agencies to tap into more groundwater. In a normal year, groundwater accounts for 40% of water supplies, according to Steven Springhorn of the California Department of Water Resources.

But that increases to 60% during droughts — and that impact, along with less water available to recharge groundwater basins, is being felt.

Of the 305,000 wells monitored by Springhorn’s department, more than 700 are dry. Of 3,200 monitoring wells, 64% are at below normal levels — including many at historic lows, Springhorn said.

The ultimate solution, of course, is more rain.

“We’re hoping for the best but planning for the worst,” he said.