The snow that blanketed the Sierra Nevada Mountains in California last winter, and that was supposed to serve as an essential source of fresh water for the drought-stricken state, was at its lowest levels in the last 500 years, according to a new study.
The paper, published on Monday in the journal Nature Climate Change, used tree-ring data from centuries-old blue oaks to provide historical context for the mountain range’s diminished snowfall. As of April 1, the snowpack levels were just 5 percent of their 50-year historical average.
The paper is the first to create a model that describes temperature and precipitation levels on the Sierra Nevada that extends centuries before researchers started measuring snow levels each year.
“The 2015 snowpack in the Sierra Nevada is unprecedented,” said Valerie Trouet, one of the authors of the study and a paleoclimatologist at the University of Arizona. “We expected it to be bad, but we certainly didn’t expect it to be the worst in the past 500 years.”
Snowmelt from the Sierra Nevada fills reservoirs that provide a third of all of the drinking water for the state of California, as well as water to fight wildfires and to generate electricity.
“The scope of this is profound,” said Thomas Painter, a snow hydrologist with NASA’s Airborne Snow Observatory. He said that models like the one developed in the study suggested a dry future for California in years beyond the current drought. “This has been a very bad drought, and being able to understand the context of it is extraordinarily important.”
To determine snowpack levels from 500 years ago, the team 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 the Central Valley. 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 then combined the precipitation data with a second data set of tree rings that looked at winter temperatures from 1500 to 1980.
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SOURCE: NY Times, Nicholas St. Fleur