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El Niño Has Helped Fill California’s Biggest Reservoir

Californians, say hello to an old friend. After four years of drought, the state’s largest reservoir is again a reservoir instead of a mudpit.

Lake Shasta, located in the northern half of the state, was down to just 29 percent of normal storage capacity as recently as December. But one of the strongest El Niño’s on record has helped steer rain to the reservoir as well as much of the rest of northern California. The result is a sight not seen in quite some time: Lake Shasta is at 109 percent of its historical capacity for this time of year, the first time that’s happened in three years.

Satellite images show Lake Shasta in April 16, 2015 (left) vs. March 29, 2016 (right). The images show the reservoir at the end of California's rainy season.
Credit: NASA Earth Observatory

You can see the progress of this rainy season thanks to Landsat images put together by NASA’s Earth Observatory.

The rest of California, however, hasn’t been quite as lucky. The end of March marks the tail end of California’s rainy season and even optimists would struggle to call the this year an overall success.

El Niño helped steer enough rain and snow to the the northern part of California to help cut into the multi-year drought that’s plagued the state. Southern California hasn’t received nearly as much precipitation and more than a third of the state is still in the most dire category of drought. Dry conditions have started to creep back into the southeast corner of the state.

 A comparison of drought in California at the start and end of the rainy season. The map pin notes where Lake Shasta is located.
Credit: U.S. Drought Monitor

Southern California needs up to 12 inches of additional precipitation to shake the drought. There is likely to be a blast of rain and snow next week, but the odds of ameliorating the drought completely at this point are slim to none.

If you needed a reminder that not all El Niño impacts are a given, this winter has certainly provided it. The southern tier of the U.S. from California to Florida has increased odds of more rain during El Niño years. Yet this winter, El Niño appears to have forsaken the western portion of that region.

In addition to dry conditions persisting in southern California, Arizona and New Mexico have been put on dry ice. This March was New Mexico’s driest March on record and Arizona’s ninth-driest so at least southern Californians have some neighbors to commiserate with.

There could be other factors beyond El Niño at play driving the drought in California and other regions of the western U.S. Recent research shows that California’s wet seasons have become hotter and drier since 1949. Whether it’s due to climate change (and if the trend continues) remains to be seen, but as Daniel Swain, author of the research, told Climate Central last week, “We need to be considering the extremes in addition to changes in the mean.”

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