California Faces ‘Gloomy’ Water-Supply Year

March 1, 2013 05:32 AM
California Faces ‘Gloomy’ Water-Supply Year

Third 2013 snow survey shows continuing dry conditions in the state.

Source: California Dept. of Water Resources

California snow surveyors confirmed Thursday that water content in the mountain snowpack is well below normal for the date.

The snowpack hasn’t actually lost much water content since the season’s first survey on Jan. 2, when it was 134% of normal for that date, but it hasn’t continued to build as winter has deepened because of the continuing warm weather that set in after the storms of late November and early December. In other words, the snowpack has not kept pace with the calendar.

As a result, the Feb. 28 snowpack water content is only 66% of average for this time of year, and only 57% of the average April 1 reading, when the snowpack normally is at its peak before beginning to melt into the state’s streams, reservoirs and aquifers.

The snowpack – often called California’s "frozen reservoir "– normally provides about a third of the water for California’s farms and communities.

With no precipitation in the forecast, the Northern California region whose storms fill key reservoirs that supply water to farms and millions of Californians is headed toward the driest January-February on record (since 1920). This is the normally rain-rich, mountainous area from Shasta Lake in the north to the American River basin in the south, where a scant 2.2" of rain has fallen since December, 13% of average. The next driest January-February was in 1991, with 4" of precipitation.

Forecasters note there could be a weather turnaround in March, but it is unlikely late-season storms will make up the water supply deficit.

"Near-record dry weather combined with pumping restrictions to protect Delta smelt are making this a gloomy water supply year," said Department of Water Resources (DWR) Director Mark Cowin. "This scenario is exactly why we need an alternative water conveyance system as proposed in the Bay Delta Conservation Plan to both protect fish species and give California a reliable water supply."

Electronic readings indicate that water content in the northern mountains is 70% of normal for the date, and 62% of the April 1 seasonal average. Electronic readings for the central Sierra show 67% of normal water content for the date and 58% of the April 1 average. The numbers for the southern Sierra are 60% of average for the date and 51% of the April 1, full-season average.

DWR and cooperating agencies conduct manual snow surveys around the first of the month from January through May. The manual measurements supplement and check the accuracy of the real-time electronic readings from sensors up and down the state.

DWR currently estimates that it will be able to deliver 40% of the slightly more than 4 million acre-feet of State Water Project (SWP) water requested for this calendar year by the 29 public agencies that supply more than 25 million people and nearly a million acres of irrigated farmland. The delivery estimate may change to reflect changing conditions.

The final allocation of State Water Project water in calendar year 2012 was 65% of requested deliveries. The initial delivery estimate for calendar year 2011 was only 25% of requested SWP water. However, as winter took hold, a near-record snowpack and heavy rains resulted in deliveries of 80% of requests in 2011. The final allocation was 50% in 2010, 40% in 2009, 35% in 2008, and 60% in 2007. The last 100% allocation -- difficult to achieve even in wet years because of pumping restrictions to protect Delta fish -- was in 2006.

Despite the dwindling snowpack, most key storage reservoirs are above or near historic levels for the date thanks to November and December storms. An exception is San Luis Reservoir, a critical offstream reservoir south of the Sacramento-San Joaquin Delta that is only at 69% of its historic level for the date. San Luis normally is filled by pumping from the Delta, but today is only 60% full because of the Delta smelt pumping restrictions.

Electronic snowpack readings may be found here
Electronic reservoir level readings are available here.

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