“We are predicting this El Niño could be among the strongest El Niños in the historical record dating back to 1950,” said Mike Halpert, deputy director of the National Oceanic and Atmospheric Administration’s Climate Prediction Center in College Park, Maryland.
“It’s very unlikely that things will develop exactly as we’re hoping for,” said Jay Lund, director of the UC Davis Center for Watershed Sciences. “In some areas, the drought might be over, and in some areas it might be worse than others.”
What could go wrong?
First, big storms could develop, but mostly hit Southern California, missing Northern California.
Last month, San Diego and Los Angeles broke records for the wettest July ever, and a highway bridge washed out in a flash flood on Interstate 10 east of Palm Springs, while the Bay Area remained mostly sunny. The disparity is a problem for California’s water supply, because many of the state’s most important reservoirs are in the north, from Shasta to Oroville to Folsom. To fill up, they need lots of water.
“If we get a lot of rain, but it doesn’t get north of Interstate 80, it won’t put as big a dent in the drought,” said Jan Null, a Saratoga meteorologist.
A second pitfall could come if big El Niño storms arrive, but they are too warm to deliver a large Sierra snowpack, or if record warm temperatures like California experienced last spring melt what mountain snow does arrive.
The Sierra snowpack is a giant bank of water in good years, holding roughly a third of the state’s water supply, then releasing it during the spring and summer months as it melts. Torrential warm winter storms will help fill dams, but much of the water could run off to the ocean, particularly if dams are nearing full capacity at the time. And those kinds of storms are more likely to cause flooding and mudslides.
“We want the snowpack for sure,” said California’s state hydrologist, Maurice Roos. “The water comes off in a much more controlled fashion. It does more good to come off gradually. It feeds the mountain streams, it has a longer duration of flow, which is good for fisheries, and it helps recharge the groundwater.”
Another risk: Nobody really knows what will happen if El Niño storms hit the “Ridiculously Resilient Ridge.” That’s the giant mass of dense high pressure off the West Coast that has blocked other storms from drenching California in recent years, largely causing the historic four-year drought. Scientists also don’t know how “the blob,” a huge mass of record-warm ocean water now stretching from California to the Pacific Northwest, might affect storms.
http://www.mercurynews.com/drought/ci_28633768/california-drought-el-nino-keeps-growing-new-report