How Many Superstorms Will It Take to End California's Drought?

Hint: More than just one.

Damian Dovarganes/AP

Weather officials expect a “storm of the decade” to wallop California Wednesday night with hurricane-force winds and torrential rainfall. While that should be good news for a state starved for water, experts have said that one storm will just not offer enough rain relief.

California has essentially lost "a winter season's worth of rain," due to its three-year drought, said Richard Seager, a climate scientist from Columbia University. The upcoming storm, the National Weather Service projects, will drop between 1 and 4 inches in urban areas and 5 to 8 inches in hilly regions. "It's been quite a while since we've seen something of this magnitude," said Austin Cross, a forecaster with the weather service, to the San Jose Mercury News. Forecasters like him are referring to the weather event as "the strongest storm so far this season and perhaps in several years."

Even with these storm predictions, weather officials say that the state still needs more rainfall, although they disagree on how much. The two central agencies which measure California’s drought recovery, the National Oceanic and Atmospheric Administration (NOAA) and the California Department of Water Resources, use very different methods, according to the Los Angeles Times. NOAA, which calculates rainfall throughout the state, reports that over the course of the next six months, California needs about 18 to 21 more inches of rain in order to bust the drought in Northern and coastal Southern California. In other words more than double the amount of rain that the state has already received all year. Inland areas of Southern California need only 6 to 9 inches. Using the expected rainfall for urban areas, California would need about six to twelve "once in a decade storms."

The other agency, the California Department of Water Resources, measures precipitation fall in the eight water stations that feed water to the State Water Project. The project is the backbone for California’s water system and distributes the resource to farmland and urban areas using reservoirs and canals. The agency reports that California needs 150 percent of its average rainfall in order to recover from the drought, or approximately 75 inches of rain by the end of this year. That would require close to a storm every 3 to 5 days for the next three months, Michael Anderson, a climatologist with the California Department of Water Resources, said to NBC. Though the superstorm may help bring California one of its wettest Decembers in a decade, weather officials agree that much more rain still is needed.