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The first indication of next year’s water supply from the Sacramento-San Joaquin River Delta is in. And it’s slightly worse than expected.

The state Department of Water Resources expects next year to export from the delta about 25 percent of the water requested by water suppliers. (They wanted 4 million acre feet; they’ll get 1 million. An acre foot is enough water to supply two homes for one year.)

The state has made that projection as what it calls an “initial allocation” — the worst-case scenario for exports from the delta, a major source of San Diego’s drinking water.

It’s the lowest initial allocation since 2003, and includes the uncertainties stemming from a federal judge’s court-ordered reduction in exports from the delta. Fresno-based U.S. District Judge Oliver Wanger earlier this year ordered a reduction in the amount of water pulled out of the delta next year, to reduce pumping when delta smelt, a tiny endangered fish, is likely to be nearby.

But the allocation is updated monthly and could increase, depending on how much precipitation falls across the Sierra Nevada this winter.

“The greatest uncertainty is December through February,” said Ken Weinberg, director of water resources at the San Diego County Water Authority. “Those are the months that make or break the [Sacramento-San Joaquin River Delta].”

Weinberg said the authority had expected the initial allocation, which is largely influenced by fall precipitation, to be slightly higher — just less than 30 percent. The full impact of the judge’s decision on the water supply won’t be known until the state begins surveying the winter snowfall in the Sierras.

The final verdict about the severity of any water shortage will be known by the end of April, Weinberg said.


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