In terms of snowfall, California's Sierra Nevada snowpack is currently at its lowest level in 500 Years Sierra Nevada Snowpack – a result of the drought that the state has been experiencing since 2012, which doesn't seem to be ending anytime soon, say researchers from the University of Arizona (UA). 

"Our study really points to the extreme character of the 2014-15 winter. This is not just unprecedented over 80 years -- it's unprecedented over 500 years," Valerie Trouet, an associate professor of dendrochronology at the UA Laboratory of Tree-Ring Research, said in a news release. "We should be prepared for this type of snow drought to occur much more frequently because of rising temperatures. Anthropogenic warming is making the drought more severe."

In an attempt to combat the drought, California Gov. Jerry Brown issued a state-wide mandatory water restriction on April 1, this past year. He instructed State Water Resources Control Board to impose a 25 percent reduction on the state's use of local water supply agencies. 

"Today we are standing on dry grass where there should be five feet of snow. This historic drought demands unprecedented action," Gov. Brown said, as he announced the restriction. "Therefore, I'm issuing an executive order mandating substantial water reductions across our state. As Californians, we must pull together and save water in every way possible."

Trouet explains that the drought is a result of reduced snowfall in 2015 and record high temperatures throughout January, February and March in California. "Snow is a natural storage system," she said in a statement. "In a summer-dry climate such as California, it's important that you can store water and access it in the summer when there's no precipitation."

According to the release, roughly 80 percent of California's precipitation happens in the winter. This precipitation is then stored and used during the summer. However, if there isn't enough snowfall to recharge these areas, summers become progressively drier and drier.

For their study of the Sierra Nevada Snowpack, researchers assessed previous studies of tree rings, which reflect the area's annual winter precipitation. From this, they were able to determine snowpack levels for the past 500 years.   

"There have been reconstructions of the drought conditions in California, but no one's looked at the snowpack in particular," Trouet said.

When comparing their findings to a temperature reconstruction created by co-author Eugene R. Wahl, from the the National Oceanic and Atmospheric Administration/National Centers for Environmental Information in Boulder, Colorado, they found that everything lined up. This means that when there was less winter precipitation and temperatures were higher, the snowpack was lower. 

Their findings were recently published in the journal Nature Climate Change.

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