High temperatures blamed for record low snowpack in 2015 on U.S. west coast

A new study blames high temperatures, not the low precipitation characteristic of past "snow drought" years, for the record low snowpack levels last year in the western-most region of the continental United States.

More than 80 percent of the snow measurement sites in the region, comprised of California, Oregon, Washington, western Nevada and western Idaho, experienced record low snowpack levels that were a result of much warmer-than-average temperatures in 2015, said Philip Mote, lead author of the study published on Monday in the journal Geophysical Research Letters.

While most of the previous records were set in 1977, when there just wasn't enough moisture to generate snow, the study suggests that greenhouse gases were a major contributor to the high temperatures, which doesn't bode well for the future.

California has been in a drought since 2011 and this multi-year period of low precipitation, by some measures, is the state's most severe in 500 years. In 2015, higher temperatures combined with low precipitation, leading to one of its lowest snowpack levels on record.

Oregon and Washington experienced much higher-than-average temperatures during the 2014-15 winter but were not as dry overall as California. Oregon was 6.5 degrees Fahrenheit warmer than average during that period.

While a total of 454 sites in the western United States, or 81 percent of the total sites, recorded record-low snowpack levels that year, the April 1 value for 111 of the sites was zero for the first time ever, essentially indicating that there was no snow left; the overall snowpack level on April 1 in California and Oregon was 90 percent below average.

"The 2015 snowpack season was an extreme year," said Mote, director of the Oregon Climate Change Research Institute at Oregon State University (OSU). "But because of the increasing influence of greenhouse gases, years like this may become commonplace over the next few decades."

Impacts of the snow drought in California, Oregon and Washington led the governors of those states to order reductions in water use and saw many ski areas, particularly those in lower elevations, struggle.

"The story of 2015 was really the exceptional warmth," said Dennis Lettenmaier, professor of geography at the University of California, Los Angeles, and co-author of the study.

"Historically, droughts in the West have mostly been associated with dry winters, and only secondarily with warmth. But 2015 was different. The primary driver of the record low snowpacks was the warm winter, especially in California, but in Oregon and Washington as well." Endit