Recent storms hint at extremes to come

“We’re nowhere near the kinds of events that we think are possible in a warming climate.” Daniel Swain, researcher at UCLA and the Nature Conservancy

The atmospheric rivers that pummeled California are a far cry from what a series of extreme storms could potentially bring, climate scientist Daniel Swain said at a legislative hearing on Wednesday that explored the impacts of the recent storm sequence.

“We’re nowhere near the kinds of events that we think are possible in a warming climate,” said Swain, a researcher at UCLA and the Nature Conservancy.

Climate change is increasing the odds that severe storms, like what Californians encountered, will happen more frequently. A warmer atmosphere can hold onto more water, which can translate to stronger storms and heavier downpours.

“There’s about a two in three chance of seeing an event that is about 20 or 30% larger than what we just experienced over the next forty years or so,” Swain said, noting that there is still uncertainty with the numbers. The risk is an upgrade from a 50-50 chance that Swain and colleagues reported previously.

Such an event would be comparable to the Great Flood of 1862, where weeks of storms pounded the state — far worse than the downpours that began on Dec. 26.

“A modern recurrence of an 1862-level flood could in 2022 dollars end up being close to a trillion — trillion with a ‘T’ — dollar disaster,” Swain said.

One way to ease the impacts of atmospheric rivers is to improve forecasts.

Researchers at the Scripps Institution of Oceanography are leading efforts to use reconnaissance flights to probe atmospheric rivers as they occur. By dropping scientific instruments — about the size of a soda can — through atmospheric rivers, flights collect details that improve weather forecasts.

The forecast for an atmospheric river event that ultimately drenched Santa Barbara County benefited dramatically from such an update.

“Until about three or four days ahead, it was aiming at the Russian River area of Northern California,” said Scripps atmospheric scientist Marty Ralph. “Then after some of our missions out offshore, the forecast shifted southward instead.”

Swain also recommended thinking about disaster preparations holistically. That means thinking of droughts and floods as related events and co-managing the risks, rather than responding to each separately.

“One thing that is becoming clear is that the historical paradigm that’s used, and management practices that we’ve been using, aren’t going to cut it in the 21st century,” Swain said.