How much will heavy rains ease California's drought?

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Tom Muneio, 61, of Santa Barbara, center, enjoys a wave in Ventura County, where sets of 8 to 10 feet pounded the coast ahead of rain storms expected late Thursday afternoon. (Rick Loomis / Los Angeles Times)

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Water covers one of several vehicles stranded in Berkeley on Thursday. A powerful storm churned through Northern California, knocking out power to tens of thousands and delaying commuters while soaking the region with much-needed rain. (Noah Berger / Associated Press)

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A major storm approaches the Los Angeles skyline Thursday, bringing with it fears of heavy rainfall, flash floods and debris. (Allen J. Schaben / Los Angeles Times)

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Matthew Hazard cleans snow from his vehicle after several inches fell in Soda Springs, Calif. A severe storm sweeping through Northern California forced drivers without four-wheel drive vehicles to put on chains before crossing over Donner Summit. (Rich Pedroncelli / Associated Press)

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People use kayaks and a canoe to make their way around a flooded parking lot at a shopping center in Healdsburg, Calif. (Eric Risberg / Associated Press)

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Beatrice Clark walks through the floodwaters in Healdsburg, Calif. Sonoma County authorities are recommending hundreds of people evacuate the lowest-lying areas near the Russian River, which is expected to start overflowing. (Christopher Chung /Associated Press)

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A resident of Guerneville, Calif., who parked his car overnight in the Safeway parking lot on Vine Street in Healdsburg, finds it submerged as Foss Creek topped its banks. (Kent Porter / Associated Press)

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An SUV is crushed by a large oak tree during a storm in San Jose. No injuries were reported. (Gary Reyes / Associated Press)

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Vehicles make their way along a snowy eastbound Interstate 80 near Soda Springs, Calif. (Rich Pedroncelli / Associated Press)

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Aidan Perez, left, 12, and Christopher Dow, 11, play with a shopping cart in the flooded parking lot of a shopping center in Healdsburg, Calif. (Eric Risberg / Associated Press)

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A car and shopping cart are submerged in water at a flooded shopping center in Healdsburg, Calif. (Eric Risberg / Associated Press)

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A vineyard is flooded along Highway 101 in Windsor, Calif., as a powerful storm churned through Northern California on Thursday. (Eric Risberg / Associated Press)

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Girls run along a flooded street in Healdsburg, Calif., during a powerful storm. (Eric Risberg / Associated Press)

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A pedestrian walks in the rain next to the San Francisco-Oakland Bay Bridge in San Francisco. (Justin Sullivan / Getty Images)

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Department of Public Works crews clear a tree that came down across a road in Larkspur, Calif. (Justin Sullivan / Getty Images)

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A pedestrian walks in traffic in San Francisco during the storm. (Justin Sullivan / Getty Images)

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Pedestrians walk through the rain in the San Francisco Bay Area. (Justin Sullivan / Getty Images)

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A man rides his bicycle through the flooded intersection in South San Francisco. (Alex Washburn / Associated Press)

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Mark Kunze of San Bruno pushes his stalled vehicle out of the flooded intersection in South San Francisco. Several vehicles stalled in and around the intersection after driving through the deep water. (Alex Washburn / Associated Press)

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Commuter ML Mann struggles in the wind and rain to make her way to catch a ferry to San Francisco from Sausalito, Calif. (Eric Risberg / Associated Press)

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Traffic moves slowly across the Golden Gate Bridge in the high winds and rain Thursday, in this view from Sausalito, Calif. (Eric Risberg / Associated Press)

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A bus passes through a flooded roadway in Mill Valley, Calif. (Eric Risberg / Associated Press)

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A car creates a wave of water while passing through a flooded area in Mill Valley, Calif. (Eric Risberg / Associated Press)

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A man crosses Montgomery Street in San Francisco. The San Francisco Bay Area reached or exceeded normal annual rainfall totals for the first time in years. (Jeff Chiu / Associated Press)

By Los Angeles Times staff

Dec. 11, 2014 11:49 AM PT

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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