STANFORD -- Stanford researchers who studied trends in the atmospheric circulation patterns that affect California's rainfall have found that conditions linked to the hot, dry weather during our latest drought have become more frequent in recent years, according to research published Friday.
That means that while this year's El Niño-driven storms may have brought temporary relief to the Golden State's parched soil and depleted reservoirs, Californians can expect more frequent droughts in the decades to come, said the study published by Science Advances.
March 12, 2016: The backyard of a home on the Sacramento River in Sacramento, Calif.
March 12, 2016: The backyard of a home on the Sacramento River in Sacramento, Calif. (Sue Morrow/Sacramento Bee via AP) )
It's a finding obscured by focusing solely on the state's precipitation, which has remained mostly steady over time. California is trending toward more extreme weather, bringing new challenges for managing our water supply. Even with an increased chance of drought, the weather patterns that trigger exceptionally wet weather also are persisting.
The researchers examined the "Ridiculously Resilient Ridge" -- a persistent area of high atmospheric pressure sitting over the north Pacific Ocean. The ridge can divert the path of storms destined for the west coast, like a boulder in a stream forces water to move around it.
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"We have a pretty narrow rainy season -- really only a handful of months to see all of our annual precipitation," says Daniel Swain, a Stanford University researcher on the study. This ridge can seriously throw off the year's rainfall total if it sits off the coast at the wrong time of year, Swain said, which has been the case during the past few drought-stricken years.
Swain's analysis found that the atmospheric conditions that lead to ridging have become more common since 1949 -- and that those triggering wet weather might also be increasing.
But California's reservoir system, which relies heavily on the Sierra Nevada snowpack to gradually replenish, wasn't set up to handle such careening conditions.
"While we can certainly fill up reservoirs with rain, that isn't going to last California in the long run," says Swain. "There's a lot of water stored in California reservoirs, but there's a lot more stored in the Sierra Nevada snowpack."Even if enough rain and snow fall over a period of several years, year-to-year inconsistency makes it challenging to manage. Steady precipitation year to year means the Sierra Nevada snowpack remains relatively constant. The melting snow provides a consistent trickle of water over the dry summer months, and wet winters build it back up again.
Prolonged drought wears that snowpack down, leaving less to melt each year. And with the warmer temperatures that often accompany severe drought, the snow melts away earlier in the spring.
Then when a deluge does come, says Swain, much of it runs into the ocean instead of the reservoirs.
The new study is part of a larger body of recent evidence predicting a shift toward extremes for California, according to Noah Diffenbaugh, a Stanford University climatologist who headed the study.
"It's clear that California is now in a different climate than the climate we had a century ago when water rights were designed, and a different climate than we had half a century ago when California's water reservoirs were built," says Diffenbaugh.
As the climate continues to change, Californians will have no choice but to adapt, said Jay Lund, a water expert at UC Davis.
"I think this is just another demonstration that California is a dry place and we have to learn to live with it for the most part," Lund said. But that can be done, he added.
"All the studies seem to indicate that if we manage the water we have well," Lund said, "California will still be a prosperous place in the future, even with more severe drought."
Contact Laurel Hamers at 408-920-5022. Follow her at Twitter.com/Arboreal_Laurel.