Californians should expect more dramatic swings between dry and wet years as the climate warms, according to a new study that found it likely that the state will be hit by devastating, widespread flooding in coming decades.
University of California researchers in essence found that the state's highly volatile climate will become more volatile as human-caused climate change tinkers with atmospheric patterns over the eastern Pacific Ocean.
The long-term average of annual precipitation in California won't change much, they predicted.
"Yet despite that, we see a big increase in extremes," said UCLA climate scientist Daniel Swain, lead author of a paper published Monday in the journal Nature Climate Change. "We expect to see more really wet years and also more really dry years."
That means managing the state's complex waterworks will become even more daunting. The threat to aging dams and flood-control networks will increase. The wildfire threat will grow more extreme.
"We really need to be thinking seriously about what we're going to do about these risks," Swain said.
"It's a little bit hard to exaggerate how disastrous a repeat of the 1862 flood would be in California," he added, referring to statewide flooding that followed weeks of storms.
That is "something that will very plausibly happen in the next 40 years," sending floodwater rushing across the Los Angeles basin and other major urban areas, he said.
The study results, based on climate model simulations, are consistent with other research findings, said Daniel Cayan, a climate researcher at Scripps Institution of Oceanography not involved in the study.
"I think they've pushed the envelope forward in elucidating how the extremes on the wet and dry side have increased," he added.
By the end of the century, California will experience a 100 to 200 percent increase in very wet years similar to the 2016-2017 rainy season that broke the state's five-year drought, the scientists found.
The frequency of serial storms on the scale of 1862 will increase 300 to 400 percent. At the same time, the rainy season will shorten as less precipitation falls in the fall and spring.
That will make it harder for dam managers, who on the one hand will have a shorter season to capture water for storage, and on the other will need to maintain reservoir space for greater storm runoff.
"Increasingly wide swings between dry and wet conditions will threaten to upset the already precarious balance between competing flood-control and water-storage imperatives in California," the researchers wrote.
In addition to accentuating the whiplash between dry and wet, global warming is shrinking the state snowpack, which acts as nature's reservoir.
"Climate change is creating a water-storage problem for California," said UCLA atmospheric sciences Prof. Alex Hall, a study co-author. "We need to think more carefully about how we capture water and how we store it."