Environment & Science

Higher temperatures are suppressing Sierra snowpack, study says

A view from the summit of Brokeoff Mountain in the Lassen National Forest.
A view from the summit of Brokeoff Mountain in the Lassen National Forest.
Miguel Vieira via Creative Commons

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Higher temperatures caused by climate change could keep the Sierra snowpack low for the foreseeable future, according to a new study from UCLA and Oregon State University.

Scientists have long known that snowpack levels can rise and fall depending on how much rain we get, but this study says that what happened with the snowpack in 2015 may have been a portent of the future.

Last year California did get some precipitation, but snowpack levels were still low because of warmer temperatures, said UCLA geographer and study co-author Dennis Lettenmaier.

That led Lettenmaier and his colleagues to surmise that rain may no longer be the main factor influencing the size of the snowpack. We may have entered a new reality in the Sierras, he said, where rising temperatures have begun to undermine snow levels.

"This pronounced signature of warming, it’s almost like a tipping point," said Lettenmaier, "where the temperature shifts into a dominant control from a secondary control on the snowpacks."

In other words, the snowpack might not return to its historic levels because it’s generally too warm to snow at the same rate now, even during wet weather.

We still should be able to turn on our taps and get water, for a number of reasons. Rainwater will help fill the reservoirs, and California water officials have a number of projects in the works – from capturing stormwater to pumping treated wastewater back into the water table.

But Lettenmaier said farmers, particularly in the Central Valley, could be in serious trouble, since they use the vast majority of the water that comes from the snowpack.

"Something takes a hit," he said. "And frankly it most likely will be agriculture. That's where the pressure point is.”"

The study, published Monday in the journal Geophysical Research Letters, also found that in 2015:

• More than 80 percent of the 454 study sites measured in California, Oregon and Washington experienced record-low snowpacks.

• California had one of the lowest snowpack levels on record, at 90 percent below average.

• At about one-fourth of the study sites, the value on April 1 was zero for the first time ever, essentially indicating that there was no snow left.