How much will heavy rains ease California’s drought?

As the biggest rainstorm in years slams into California, some are wondering how much it will mitigate California’s epic drought.

The rain will definitely help. But by any measure, the drought is far from over.

The storm is expected to dump 2 to 8 inches of rain in the San Francisco area and 2 to 5 inches in parts of Southern California through Saturday.

As The Times’ Matt Stevens reported, the National Oceanic and Atmospheric Administration says 18 to 21 more inches of rain over six months would do the trick for most of the state.


That’s a tall order since the state’s average rainfall for the year is about 23 inches. The latest storm dumped only about 1.5 inches in downtown L.A. but more than three inches in wetter parts of Northern California that feed the State Water Project.

Measuring drought recovery is a tricky business. And two key agencies — NOAA and the California Department of Water Resources — do it in significantly different ways.

State water resource officials said this week that it would take 150% of the average rainfall for California to recover from the current drought. The DWR measures rainfall at eight stations in the northern Sierra because water from those areas feeds the State Water Project. The water project, in turn, delivers water to farmland in the Central Valley and urban Southern California through a vast network of reservoirs and canals.

An average of 50 inches of rain fell at those stations annually between 1922 and 1998. Using that average, officials said 75 inches of rain would need to fall in those Northern California spots by the end of the year to end the drought.

Since Oct. 1, only about 11 inches of rain has fallen at those eight stations.

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