Fire risk: Calif. snowpack at lowest level in 500 years

The snowpack in California’s Sierra Nevada 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, in its fourth year, and raises the prospect of more water shortages that could impact agriculture and hydroelectric power production, and exacerbate wildfires.

“Our study really points to the extreme character of the 2014-15 winter,” said study lead author Valerie Trouet of the University of Arizona’s Laboratory of Tree-Ring Research.

Where there is usually about 5 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, Trouet said.

“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 data sets, they could see how much snow fell each winter.

The trees aren’t harmed by the testing, as the scientists 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 said man-made global warming is making the drought in California more severe.