Storms erase chunk of state’s snow-water deficit

Think of the snow that falls each winter in the Sierra Nevada as something like a paycheck for California’s water supply. The mountain snow melts and flows into downstream reservoirs, helping pay the “bills” for the state’s agricultural, urban and environmental water supply needs through the hot, dry summer and fall.

A drought, then, like the historic one that has gripped California for five-plus years and provided little mountain snowfall, is a lot like getting laid off.

“We were basically unemployed for five years when it come came to our (water) income,” said Noah Molotch, director of the Center for Water Earth Science & Technology at the University of Colorado, Boulder.

A surprisingly strong start to California’s winter has put its water supply back to work — and a substantial amount back in the bank, Molotch said Monday.

Molotch led research that found that the storms known as atmospheric rivers that pummeled California from late December to late January appear to have recouped by more than a third the water deficit associated with lower-than-average snowpack during the drought years.

Using NASA satellite readings and state snow-sensor data, Molotch estimated the two largest storms in a three-week stretch dumped enough Sierra snow to supply the state with roughly 17.5 million acre-feet of water. That’s nearly four times the capacity of Shasta Lake, the state’s largest reservoir.

Compared to pre-drought years, the amount of snow that fell in that span represents more than 120 percent of the typical annual snow accumulation for the Sierra, Molotch said.

While 2017 is off to a promising start, California continues to face an overall water deficit of nearly 36.5 million acre-feet because of the cumulative effects of the drought, largely related to depletion of the state’s groundwater supplies. Molotch said that during the drought some regions have been drawing more than 80 percent of their water supplies from the ground.

“We’ve drawn heavily out of our savings, and it’s going to take us more than one wet winter to recover that savings,” Molotch said.

That wet weather should continue this week, with another storm system expected to roll into the Sacramento region Wednesday. The National Weather Service said light precipitation will start Wednesday night, become more widespread Thursday and linger through Saturday.

The Sierra could receive up to 2 feet of snow along mountain passes. In the Central Valley, the weather service warns of wind gusts of up to 40 mph on Thursday. Sacramento, which received 9.85 inches of rain in January, could see another 2 inches by the time the storm passes.