A low-to-no snow future and its impacts on #water resources in the western United States — Nature.com #snowpack #ActOnClimate

Westwide SNOTEL basin-filled map December 4, 2021 via the NRCS.

Click this link for web access to the paper.

From The Washington Post (Diana Leonard):

A new study provides a glimpse into the future of Western U.S. snow and the picture is far from rosy: In about 35 to 60 years, mountainous states are projected to be nearly snowless for years at a time if greenhouse gas emissions continue unchecked and climate change does not slow.

Due to rising temperatures, the region has already lost 20 percent of its snowpack since the 1950s. That’s enough water to fill Lake Mead, the nation’s largest human-made reservoir. It stands to lose another half, and possibly more, later this century, from the Rockies to the Sierra Nevada and into the Cascades of the Pacific Northwest, according to a literature synthesis conducted in the study leveraging dozens of peer-reviewed climate model projections.

The current snow situation in the West offers a preview of what the future may hold. Snow water equivalent, or the liquid water from snowpack, is much lower than normal in much of the Western United States. Snow cover across the nation is only at 6 percent — the lowest since records began in 2003.

Decades ahead, the “potential for persistent low-to-no snow to disrupt the [Western U.S.] water system is substantial, potentially even catastrophic,” the study’s authors write…

Published in Nature Reviews Earth and Environment in October, the paper provides an overview of how Western snowpack has changed and what it will look like over the course of this century.

In addition to the 20 percent loss, snowpack is peaking and melting off earlier in the year and is expected to continue on that track. Atmospheric rivers are also warming and dropping more rain than snow, which increases flood risk.
The demands of a warmer atmosphere are already translating into water stress. Although this past year was not a “low snow” year for California, much less snowmelt made it to reservoirs because of an unusually warm spring.

From Denver Water (Kim Unger):

Snowpack: Here today, gone tomorrow?: A recent study finds that climate change means less water from melting snow. So what are we doing about it?

Denver Water employees stationed in Winter Park take measurements of snowpack in 2014. Photo credit: Denver Water.

Denver Water’s extensive reservoir system helps us monitor water supplies, even as a new climate change study warns of a shrinking snowpack.

A 2015 study from the Earth Institute at Columbia University found that the snowpack in the Northern Hemisphere has a 67% risk of declining — greatly reducing the amount of drinking water available from that source.

The study focused on river basins that rely on snowpack and are not adequately replenished by rainwater. The study identified the Colorado River basin among those at high risk for greatly reduced snowpack in the future, when demand for water will outpace availability. The river provides water to seven states, including Colorado.

As worrisome as that sounds, the study doesn’t provide a complete picture of how climate change may affect Denver’s water supplies, said Laurna Kaatz, Denver Water’s climate adaptation program manager.

She isn’t raising any alarm bells.

“This study is a big-picture look at how sensitive systems are to different conditions,” Kaatz said. “It’s not a deep examination into the full range of possible climate changes Colorado could experience in the future.” Nor does it dive into how water managers in Colorado are contending with those potential changes.

“We have to consider all of the local variables in our planning,” she said.

Those variables include population growth, how efficiently customers use water, environmental and ecosystem needs, and local climate and weather patterns.

Denver Water’s supply is mostly from snowpack. The snowpack — the total amount of ice and snow on the ground — fluctuates from year to year. In warm, dry years, it can be gone by mid-summer; in wet years it can last through the next winter season.

“Our region experiences huge fluctuations — or variability — in weather and climate conditions,” Kaatz said. “Fluctuations, especially in precipitation, mean that the rivers and streams that supply our water are also highly variable. This is why reservoirs are so important in Colorado. Colorado’s high peaks protect the snow for months out of the year, and our strong reservoir system protects our water supply against seasonal and annual variability.”

Making sure water is available when customers need it requires careful management of how water flows in and out of reservoirs. Kaatz explained, that when the snowpack melts, we capture what we need and store it for future use. In years of drought, reservoir levels go down, and customers need to be even more conscious of water use.

Denver Water works with the scientific community to stay up-to-date on the latest models and trends because we live in such a variable climate.

“As the climate continues to warm, we do anticipate that snowpack will not live as long into the summer and fall months, especially in warm, dry summer and fall seasons, and that variability will increase,” Kaatz said. “At Denver Water, we plan for the long-term and look at the many different challenges we could be up against in the future, including climate change.”

While the study gives a potential glimpse into our water future, the full story is really told in how well Coloradans have embraced water conservation. Water use by Denver Water customers between January and May 2021 represented the lowest usage for those months since 1968.

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