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    Where did Sierra snow go this spring? Not into California rivers and water supplies

    Massive amounts of water the state was counting on soaked into the ground or evaporated

    California’s severe drought was made worse this year by a shocking surprise.

    Every year, much of the drinking water that flows through the taps of millions of Californians begins in the Sierra Nevada. Snow and rain fall on the vast mountain range during the winter months, and the water moves downhill into streams, rivers and reservoirs in the spring and summer.

    But this year, in a trend that startled water managers, much of that runoff simply vanished.

    State water planners say that 685,000 acre-feet of water that they had forecast as runoff in the Northern Sierra — or 40% more water than the city of Los Angeles uses in a year — failed to arrive. After two years of extreme drought, the ground was so dry that the water soaked in before making it down the mountain. Warmer-than-normal temperatures in April and May also caused significant amounts to evaporate.

    “The snowpack was disappearing and the rivers weren’t rising,” said Sean de Guzman, chief of snow surveys and water supply forecasting for the California Department of Water Resources in Sacramento. “A lot of our forecasts were off.”

    The expected water never made it to reservoirs, which now sit far below historic averages. That lack of runoff is contributing to water shortages in cities and farms across the state.

    “We have 100 years of data saying if you have this much snow, you would expect this much runoff,” de Guzman said. “But that fell apart this year.”

    The snowpack provides nearly a third of California’s water supply for cities and farms, including filling the Hetch Hetchy system and the Sacramento-San Joaquin River Delta that are critical water sources for the Bay Area.

    The Northern Sierra, with the most precipitation, is the most important part.

    In an average year, about 6.3 million acre-feet of runoff comes from the Northern Sierra, according to the Department of Water Resources. This, spring, following two very dry winters, state forecasters predicted 2.3 million would run off. But only 1.6 million arrived. An acre-foot is the amount of water it takes to cover an acre of land one foot deep.

    Put another way, the missing 685,000 acre-feet is 223 billion gallons, or more than twice as much water as every home, business and farm in Santa Clara County uses in a year.

    The Sierra snowpack is gone now. Apart from a few tiny pockets at high elevations, it has melted.

    Earlier in the spring, the situation looked bad, but not terrible.