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California Epic Drought Leads to Lowest Snowpack in 500 Years

Climate

The snowpack for the state of California—a critical source of drinking water for the state—hit its lowest level in the last 500 years, according to a study published yesterday in Nature. When the snowpack was measured in April—historically the high point for the season's snowpack—it was just 6 percent of average for the past century.

Now, thanks to this latest study, we know that the snowpack hasn't been this low in at least five centuries. The study used tree-ring data from centuries-old blue oaks to provide historical context for this year's extremely low snowpack. The paper is the first of its kind in describing temperature and precipitation levels in the Sierra Nevada "that extends centuries before researchers started measuring snow levels each year," says The New York Times.

The latest findings reveal the 2015 snowpack was far below normal for the last 500 years. Photo credit: Laboratory of Tree-Ring Research, University of Arizona

“The 2015 snowpack in the Sierra Nevada is unprecedented,” Valerie Trouet, one of the authors of the study, told The Times. “We expected it to be bad, but we certainly didn’t expect it to be the worst in the past 500 years.”

Last winter was the hottest on record for California, so the little precipitation the state received often fell as rain and not snow. This has grave implications for the state's water supply because snowmelt provides one-third of the state's drinking water and is also critical for fighting the state's increasing wildfires. California is in the midst of a four-year drought that has produced devastating wildfires like the Valley Fire in Northern California, which is happening right now. This past spring, NASA scientist Jay Famiglietti warned that Californians only have one year of water left in the state's reservoirs.

Over the last few years, winter precipitation has been far below normal, sending the state into a deep drought. Photo credit: Climate Central

“The scope of this is profound,” Thomas Painter, a snow hydrologist with NASA’s Airborne Snow Observatory, told The Times. “This has been a very bad drought, and being able to understand the context of it is extraordinarily important.”

To determine snowpack levels that far back, researchers combined two data sets of blue oak tree rings. "The first set provided historical precipitation levels from more than 1,500 blue oaks from 33 sites in California’s Central Valley," explains The Times. "The team compared part of that data from the years 1930 to 1980 with actual snowpack measurements and found that both findings matched. Using this correlation, the team combined the precipitation data with a second data set of tree rings that looked at winter temperatures from 1500 to 1980." Based on the 500-year record, researchers estimated the odds of such a low snowpack happening more than once over that time period were less than five percent.

Satellite images show the Sierra snowpack in 2015 compared to 2010. Photo credit: NASA / MODIS

While the April 1 assessment finally goaded state officials into action with Gov. Jerry Brown issuing the state's first-ever mandatory water restrictions, many scientists saw this coming. Peter Gleick, president and co-founder of the water policy-focused Pacific Institute began investigating the impacts of climate change on California's water supply 30 years ago.

“It’s shocking in a historical context because we’ve never seen this bad of a snowpack. It was not shocking in the sense that we sort of knew this was coming, and we just didn’t know when,” Gleick told Climate Central. “This is the new unpleasant reality” for Western water, not just California.

And don't expect the strong El Niño to "solve the drought" as warmer Pacific Ocean waters are expected to bring lots of precipitation to California this winter. Even if the state receives the much-needed rainfall, the storms might not produce a larger snowpack. If temperatures remain above-average as expected, much of that precipitation could fall as rain and not snow even at higher elevations—just as they did this past winter. Furthermore, Kirsten James at Ceres explains that because of climate change and poor water management, El Niño—not even a Monster El Niño—can't save California from its epic drought.

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The last time San Francisco did not record a drop of rain in February was in 1864 as the Civil War raged.

"This hasn't happened in 150 years or more," said Daniel Swain, a climate scientist at UCLA's Institute of the Environment and Sustainability to The Guardian. "There have even been a couple [of] wildfires – which is definitely not something you typically hear about in the middle of winter."

While the Pacific Northwest has flooded from heavy rains, the southern part of the West Coast has seen one storm after another pass by. Last week, the U.S. Drought Monitor said more Californians are in drought conditions than at any time during 2019, as The Weather Channel reported.

On Thursday, the U.S. Drought Monitor said nearly 60 percent of the state was abnormally dry, up from 46 percent just last week, according to The Mercury News in San Jose.

The dry winter has included areas that have seen devastating fires recently, including Sonoma, Napa, Lake and Mendocino counties. If the dry conditions continue, those areas will once again have dangerously high fire conditions, according to The Mercury News.

"Given what we've seen so far this year and the forecast for the next few weeks, I do think it's pretty likely we'll end up in some degree of drought by this summer," said Swain, as The Mercury News reported.

Another alarming sign of an impending drought is the decreased snowpack in the Sierra Nevada Mountain range. The National Weather Service posted to Twitter a side-by-side comparison of snowpack from February 2019 and from this year, illustrating the puny snowpack this year. The snow accumulated in the Sierra Nevadas provides water to roughly 30 percent of the state, according to NBC Los Angeles.

Right now, the snowpack is at 53 percent of its normal volume after two warm and dry months to start the year. It is a remarkable decline, considering that the snowpack started 2020 at 90 percent of its historical average, as The Guardian reported.

"Those numbers are going to continue to go down," said Swain. "I would guess that the 1 March number is going to be less than 50 percent."

The National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center forecast that the drier-than-average conditions may last through April.

NOAA said Northern California will continue deeper into drought through the end of April, citing that the "persistent high pressure over the North Pacific Ocean is expected to continue, diverting storm systems to the north and south and away from California and parts of the Southwest," as The Weather Channel reported.

As the climate crisis escalates and the world continues to heat up, California should expect to see water drawn out of its ecosystem, making the state warmer and drier. Increased heat will lead to further loss of snow, both as less falls and as more of it melts quickly, according to The Guardian.

"We aren't going to necessarily see less rain, it's just that that rain goes less far. That's a future where the flood risk extends, with bigger wetter storms in a warming world," said Swain, as The Guardian reported.

The Guardian noted that while California's reservoirs are currently near capacity, the more immediate impact of the warm, dry winter will be how it raises the fire danger as trees and grasslands dry out.

"The plants and the forests don't benefit from the water storage reservoirs," said Swain, as The Mercury News reported. "If conditions remain very dry heading into summer, the landscape and vegetation is definitely going to feel it this year. From a wildfire perspective, the dry years do tend to be the bad fire years, especially in Northern California."

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