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California’s snowpack, aided by atmospheric rivers, could help drought

A coat of fresh snow is seen on a mountain in South Lake Tahoe, Calif., the morning after a winter storm pelted the region with a large amount of snow on Jan. 1. (Stephen Lam/AP)
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At Andrew Schwartz’s office, California’s parade of atmospheric rivers swamped the basement and lab, drenching equipment in inches of water. The power has gone out repeatedly, sometimes for more than two days straight.

But none of that has dimmed the joy of watching snow pile up so high that it has engulfed the second-story windows at his remote outpost high in the Sierra Nevada mountains, where he studies California snowpack and what it means for the drought-parched state’s water supply. By snowshoe, he has trudged through mounds of white more than 9 feet deep as he takes measurements at the UC Berkeley Central Sierra Snow Laboratory, a collection of buildings and monitoring equipment along the Donner Pass. On New Year’s Eve, he went sledding.

“It’s kind of been heaven watching it fall,” said Schwartz, the lab’s lead scientist and manager.

The dumping of snow in the Sierra Nevada over the past two weeks has come as a great relief to those who monitor mountain snowpack, a crucial source of water that fills the state’s reservoirs and will determine how long California must endure its relentless drought. While researchers caution that even this abundance of accumulation — which has reached about 15 feet in some parts of the mountains — could still be wiped out by exceptionally hot or dry conditions later in the year, the buildup of snowpack is ahead of schedule and amounts to good news for the state’s battered reservoirs.

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The Sierra Nevada snowpack across California has reached 226 percent of normal for this time of year, according to the state Department of Water Resources. During the prior winter, California was also hit by big December storms that led to early snow accumulation totals far above average, only to endure the driest three-month start to the year in state history, leading to the third consecutive year of drought. The more important moment of assessment comes on April 1, what Schwartz called the “golden date” for snow measurement, because that has traditionally been around when snowpacks are deepest and an important data point in modeling the year’s coming water supply.

The current snowpack has even surpassed the April 1 average, at 102 percent of normal, Schwartz noted.

“We didn’t even come close to that last year,” he said. “If we’re above that [April 1 average], typically it means that we’re going to be in a good water year, we can potentially look at coming out of the drought.”

The battering ram of storms that hit the California coast has meant catastrophe in many parts of the state, with extensive flooding, mass evacuations, power outages, downed trees, breeched levees, mudslides, and the deaths of at least 18 people. The whiplash of extremes brought by climate change — from too little water to too much — has brought a new round of costly destruction to residents more accustomed to the ravages of smoke, fire and dry wells.

California’s paradox: Confronting too little water, and too much

The storm that hit the California coast on Wednesday was the seventh in a series of nine expected storms moving in from the Pacific Ocean since Christmas. Over the past week, some areas, such the Santa Barbara region, have received up to 15 inches of rain in one day.

The abundant precipitation has already boosted California reservoir levels, although the largest ones — Lake Shasta and Lake Oroville — remain less than half full and below averages. Across the state, reservoirs are currently at 84 percent of average, Molly White, water operations manager for the State Water Project, told a briefing for reporters Wednesday.

“Unfortunately, they still have a lot of road to go until they get back to average,” Michael Anderson, the state climatologist with the Department of Water Resources, said at the briefing, referring to Shasta and Oroville. “The good news is they’re off historic lows. The challenge is that they still have a lot of recovery to make before they would be back to normal operating conditions.”

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The recent storms have not had much impact on the Colorado River Basin, another important source of water for California. That region is also enduring a historic drought and facing dramatic cuts in water usage as levels in major reservoirs Lake Powell and Lake Mead have fallen to dangerous levels. The atmospheric rivers — narrow but intense filaments of deep tropical moisture stretching thousands of miles across the Pacific — that have drenched the California coast and mountains haven’t had the same impact further inland. Snowpacks in the Upper Colorado River Basin states — Colorado, New Mexico, Utah and Wyoming — are above average for this time of year, although not as high as California.

But the past two years have also seen relatively bountiful snows in the Rockies, only to have runoff levels far lower than average. That’s because hotter temperatures in recent decades have dried out soils, hastened melting, increased evaporation and lengthened growing seasons, so vegetation consumes more water before it can reach the reservoirs, said Katrina Bennett, a hydrologist at Los Alamos National Laboratory who studies the relationship between snowpack and water supply in the Colorado River region.

“Even with these very high years, we’re still seeing aridity across the basin, and that’s largely due to the fact that we still have this background of higher temperatures,” she said. “If we did have very, very high years, several years in a row, we might see some correction in the reservoir systems.”

“It’s really almost too early for us to say, ‘Yes, this is going to help us.’ I think we have to see how the rest of the year really plays out in terms of the weather system and climate impacts,” Bennett added.

During this wave of storms in California, the freezing elevation has been around 5,000 feet. Schwartz noted that some of the deepest snowpacks after these recent storms are in the southern Sierra Nevada.

“The great thing is, that’s where they’ve needed the moisture the most, realistically,” he said. “It’s statewide, but the areas that have needed it the most in Southern California are the ones getting the most now.”

On Wednesday morning, the flakes had tapered off at Schwartz’s mountain field station, but more storms were headed his way in coming days.

“We’re in a really favorable spot,” he said.

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