September historical average 1,370,612 acre-feet
September 2015 644,340 acre-feet
September 1977 (dry year) 306,790 acre-feet
September 1983 (wet year) 1,704,972 acre-feet

How dry is California?

By Katie Park
Oct. 13, 2015

California is in the fourth year of its most severe drought on record, facing low precipitation, dwindling mountain snowpack levels and the hottest temperatures in state history. The water supply in the state’s reservoirs has dropped to historic lows, especially in the central part of the state.

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Take a look at Don Pedro, a large reservoir in the San Joaquin River Basin, where the drought is especially severe. Historically, the reservoir would be nearly 70 percent full in the month of September.

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Here’s the water level for Don Pedro in September of this year. It's more than 236 billion gallons lower than average, about the quantity of 358,000 Olympic-sized swimming pools.

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Levels for the reservoir haven’t dipped as low as they did during a dry year in 1977. But the 1976-77 drought lasted only two years, while the current drought is in its fourth year.

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Here's how the reservoir levels compare over the course of a water year, which runs from October 1 through September.

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What does this mean for the Southwest?

The region’s potential for drought has increased due to rising temperatures, sparse precipitation and a record low quantity of melting mountain snow.

Catastrophic wildfires have raged through the western U.S. in one of its worst wildfire seasons ever. More than 9 million acres have burned nationwide this year, the second highest number on record.

Climate scientists estimate that California would need two to three times as much rain as normal to resolve its precipitation debt. In Southern California, that would mean nearly 53 inches of rain.