It’s not just that wet years bring more water; it’s also how the water is falling. Because temperatures are warmer, a lot more of California’s precipitation has in recent years been falling as rain instead of snow. This is a problem for a few reasons.
Snow acts as a kind of “frozen reservoir” that stores water from one season to another — the snow falls in the winter, then trickles into California’s water supply as it melts. But when precipitation falls more heavily as rain — and when the storms come in quick succession, as they have recently — water isn’t as easily stored and instead becomes destructive.
A 2019 study published in the journal Water Resources Research found that the risk of flood grows as snowfall shifts to rainfall and that floods driven by rain can be much larger than floods driven by snowmelt. When rain falls on snow, the snow melts faster. And when rain pours on cities, little of it is captured for use — and instead washes out to sea.
And so we’re left with this surreal phenomenon of a flood-drenched drought. As the storms pounded California last week, water-management officials were telling people not to go wild with water: “We’re kind of dealing with this extreme flood during an extreme drought, and so we’re, of course, encouraging Californians to continue to conserve water and make conservation a way of life,” one official told The Los Angeles Times.
Water experts say there are ways to mitigate the effects of California’s changing climate on our water supply. Gleick has called for revamping national flood insurance regulations to curtail rebuilding in places that are newly prone to flooding. Leaving some places undeveloped and allowing areas to regularly flood will help recharge California’s groundwater supply, he said.
Capturing storm water is another big opportunity. For years, Los Angeles County has been working on a gigantic effort to collect more rainfall for use. Among other projects, the plan involves creating huge “spreading grounds” — tracts of land where rainwater is allowed to pool and soak into the ground; installing rain barrels and other ways to collect water in apartment buildings and at businesses; and building water-absorbing infrastructure into roadways and sidewalks, like drainage ditches and pavement made out of materials permeable to water. Officials reported collecting 33 billion gallons of water in the recent storms — enough for more than 800,000 people for a year. Expanding such efforts statewide could yield lots of new water.
It’s also clear that California’s agricultural sector has got to use less water. Farming currently accounts for 80 percent of California’s water use. In drought years, lots of the agricultural water is pumped from underground, a practice that experts say cannot be sustained. Farmers can reduce this amount by growing more efficient crops — at the moment too much of our land is used to grow water-hogging crops like alfalfa and almonds — but even so, the agricultural sector will have to get smaller. Farmland will need to be fallowed — at least 500,000 acres, according to researchers at the Public Policy Institute of California.