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Photo: Brandy Saturley / Flickr

Skiing in July? It could happen this year, but California’s days of bountiful snow are numbered.

After five years of drought and water restrictions, the state is reeling from its wettest winter in two decades. Moisture-laden storms have turned brown hillsides lush green and state reservoirs are overflowing. There’s so much snow, Mammoth Mountain resort plans to be open for business on Fourth of July weekend.

But whether or not the drought is officially over — Governor Jerry Brown won’t make that call until the Sierra Nevada snowpack is assessed again in April — the state is caught in the crosshairs of climate change.

Apart from the slopes, the Sierra snowpack provides water for agriculture and millions of people via a vast network of dams and reservoirs. According to a UCLA study out today in the Geophysical Research Letters, that system faces serious threats from warming temperatures.

This year, the atmospheric rivers that bring winter storms to the western United States happen to be particularly numerous, leading to much-needed snowpack replenishment. Warm air holds more water, but it also causes precipitation to fall as rain instead of snow.

The phenomenon is one climate change impact that adversely affects the Sierra Nevada snowpack, said Alex Hall, a UCLA climate scientist. Hall and study co-author Neil Berg modeled what California droughts will look like in terms of snowpack loss.

“The cryosphere — frozen parts of the planet — has shown the earliest and largest signs of change,” Hall said. “The Sierra Nevada are the little piece of the cryosphere that sits right here in California.”

The iconic mountain range provides 60 percent of the state’s water. But a frozen resource that gradually melts and recharges reservoirs is particularly vulnerable to a warming climate and droughts that are expected to become increasingly severe. Warming causes a greater share of precipitation to fall as rain, and snow to melt more rapidly.

Besides offering a window into the future, the UCLA study revealed some climate effects that are already being felt. Sierra Nevada snowpack in the 2011-2012 and 2014-2015 winters was 25 percent below what it would have been without human-induced warming. The effect was even worse at elevations below 8,000 feet, where snow cover decreased by up to 43 percent.

“Seeing a reduction of a quarter of the entire snowpack right now — not 20, 30 or 40 years from now — was really surprising. It was almost as if 2015 was the new 2050 in terms of the impacts we were expecting to see,” said Berg.

To accurately simulate the drought-altered Sierra snowpack, researchers combined finely calibrated atmospheric, snow and topography modelling. They cross-referenced their results with satellite information and on-the-ground “snow pillows” — devices that measure snow’s water content. They also simulated pre-industrial era snowpack, to understand how much human-induced climate change is affecting snow loss now.

Hall and Berg’s computer modeled data (left) closely resembles NASA satellite imagery of actual Sierra Nevada snowpack (right).

Hall and Berg’s computer modeled data (left) closely resembles NASA satellite imagery of actual Sierra Nevada snowpack (right).

By the end of the current century, conditions could be even worse. If humans continue emitting greenhouse gases in a business-as-usual scenario, average temperatures in the Sierras are projected to rise up to 10 degrees, causing the snowpack to decrease during drought by a massive 85 percent. There would be almost no snow at altitudes below 8,000 feet. From a water resources perspective, an 85 percent loss would be as if there was no snow in the Sierras at all, Berg said.

Four scenarios for the Sierra Nevada snowpack under drought conditions. The measurement shown is the amount of water contained in the snowpack, averaged over the mountain range.

Four scenarios for the Sierra Nevada snowpack under drought conditions. The measurement shown is the amount of water contained in the snowpack, averaged over the mountain range.

Things don’t look much better if nations follow the United Nations’ Paris climate agreement, which seeks to limit global warming at 1.5/2 degrees Celsius. Even with such mitigations, snowpack during a drought like the one we recently experienced is projected to drop 60 percent by century’s end.

Berg said he found the results sobering. “I feel like I’m living through a walking history book, where we’re seeing these major events unfold right before our eyes.”

An erratic and dwindling snowpack means California needs to rapidly re-configure its water storage systems and management practices, UCLA’s Alex Hall said. “I think there are serious questions about the suitability of the current water storage infrastructure as we go forward.”

Typically, the amount of water accumulated in the snowpack is roughly equivalent to what reservoirs can store. As things heat up and snow melts earlier, “there’ll be a real storage problem and water will have to be let go,” Hall said.

Hall believes the best solution is utilizing groundwater aquifers as a capture and storage mechanism. “The storage potential of groundwater aquifers is enormous, it’s probably ten times larger than the reservoir capacity.”

California doesn’t have the greatest track record with groundwater, which was severely depleted during the drought, particularly for agricultural irrigation.

The state legislature is taking steps to improve the situation, passing the Sustainable Groundwater Regulation Act in 2014 and launching small pilot projects in the Central Valley, where farmers are paid to flood their fields to allow groundwater infiltration and recharge.

But with climate change altering the state’s snowpack in ways scientists believed was decades away, those efforts aren’t enough, Hall said.

“It needs to be on a much larger scale. We’re moving in the right direction, but it’s not nearly enough. We need to scale up these efforts and we need to be starting now.”

This post was originally published UCLA’s Institute of the Environment and Sustainability’s website and has been republished here with permission of the author.

One Response

  1. Excellent piece.

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