California's Sierra Nevada snowpack falls to 500-year low, worse than expected
The Sierra Nevada snowpack, which is a critical water source for California, has fallen to a 500-year low, much worse than experts had estimated, which will cause further alarm for an area that is already suffering from four years of drought.  California relies on almost all of its precipitation in the winter months, as come April, when the snow melts, the water flows into streams and reservoirs to prepare for the warm months ahead.  The snow accumulation in the mountains, however, was only 5% of what is normal, which will inflate the risks of wildfires, dry up wells, instigate water rationing and affect agriculture.
Doyle Rice

USA TODAY

The snowpack in California’s Sierra Nevada mountains this year has fallen to its lowest level in at least the past 500 years, according to a study published Monday in Nature Climate Change, a peer-reviewed British journal.

The finding underscores the severe drought afflicting the state, now in its fourth year, and raises the prospect of more water shortages that could impact agriculture and hydroelectric power production, and exacerbate wildfires.

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"Our study really points to the extreme character of the 2014-15 winter," said study lead author Valerie Trouet of the Univeristy of Arizona's Laboratory of Tree-Ring Research.

Where there is usually about five feet of snow, there was bare ground at the snow survey site in the Sierra on April 1.

"This is not just unprecedented over 80 years — it's unprecedented over 500 years," she said.

The Sierra Nevada snowpack plays a critical role in replenishing the state’s water reservoirs and provides 30% of the state's water supply, according to the study.

Though actual snowpack measurements have been taken in California over the past few decades, climate scientists need to use other methods, known as proxies, to determine weather patterns for previous centuries.

By looking at the rings of more than 1,500 trees in California and other trees across the West, scientists can tell how much snow fell for each winter over the past five centuries, according to Trouet.

"Trees are remarkable ... they are the best recorder of past climate," she said. Trees like water, she said, so wide rings signify a wet winter while narrow rings show it was a dry winter.

Trouet used one species of tree — the blue oak — to determine precipitation, and a variety of other species to determine temperature. By cross-referencing the two data sets, they could see how much snow fell each winter.

The trees aren't harmed by the testing, as the scientists just bore holes in the tree and pull out a chunk to look at the rings.

"We should be prepared for this type of snow drought to occur much more frequently because of rising temperatures," Trouet said. She added that man-made global warming is making the drought in California more severe.

"This new study reinforces our understanding of the severity and extreme nature of the current drought," said research scientist Jeffrey Deems of the National Snow and Ice Data Center in Colorado, who was not part of the study.

"Furthermore, the new reconstructed paleohydrology indicates that the climate system has produced droughts similar to (or even more intense than) the current one in the past," Deems said. "Recent and projected trends toward warmer and drier conditions should therefore be of great concern," he added.