Manage water resources in a snow-free or low-snow future

New analysis from Berkeley Lab reveals that if greenhouse gas emissions continue under the high emissions scenario, winters with little or no snow will become a regular occurrence in the western United States by 35 to 60 years. (Credit: Melissa Kopka / iStock)

Snow coats in the mountains around the world are declining, and if the planet continues to warm, climate models predict that snowpack could decrease dramatically and possibly even disappear completely over some mountains, including the western United States, over the next year. century. New study by researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) analyzes the likely timeline for a snow-free future, what it will mean for water management, and investment opportunities now that could avoid consequences catastrophic.

Their journal article, “A future without snow and its impacts on water resources in the western United States” published in the journal Nature Reviews Earth and Environment, analyzes previous climate projections and finds that if greenhouse gas emissions continue along the high emissions scenario, winters with little or no snow will become a regular occurrence in the western United States within 35 to 60 years. In addition, the study reassesses long-held assumptions about water management in the United States and emphasizes that scientists and water managers need to collaborate more closely to develop and implement water management strategies. adaptation to climate.

The Sierra Nevada, Rockies, Cascades, and other mountain ranges provide tremendous service by capturing, storing, and releasing water for downstream use. Historically, the timing of snowmelt provides a critical delay in the delivery of water supply in spring and summer, when rainfall is low and water demands are at their peak due to agriculture. The factors causing the decrease in the snowpack are mainly related to the increase in temperature and the change in precipitation characteristics. Warmer temperatures also mean that storms will produce more precipitation and less snowfall, limiting the amount of snow accumulated during the winter.

The research, co-led by authors Erica Siirila-Woodburn and Alan Rhoades of Berkeley Lab’s Earth and Environmental Sciences Space, begins with a review of the literature which distills several hundred scientific studies on snow removal; among these, they identify and analyze 18 studies that had quantitative snowpack projections for the western United States

When will the future arrive with little or no snow?

“A recent study pointed out that there has been a 21% drop in snowpack water storage on April 1 in the western United States since the 1950s, which is equivalent to the storage capacity of Lake Mead. In our review, we found that by mid-century we should expect a comparable decline in snowpack, ”said Rhoades. “By the end of the century, the decline could reach more than 50%, but with a greater margin of uncertainty. “

Many water managers use the somewhat arbitrary date of April 1 to make snowpack observations and make planning decisions. In recent decades, there have been decreases in peak snowpack volume as well as earlier occurrences of the time of the snowpack peak, with the peak occurring about 8 days earlier in the year for each degree Celsius ( 1.8 degrees Fahrenheit) of warming.

Many regions have already experienced very little snowy winters in recent years, such as the Sierras in 2015 where the level of the snowpack on April 1 was 5% of normal, which the authors describe as an “extreme” event. The article defines two other types of light to no snow conditions – “episodic light to no snow”, or when more than half of a mountain basin experiences light to no snow for five consecutive years, and “little or no snow. no snow “, in which this occurs for 10 consecutive years.” Little snow “is defined as when the snowpack (or more precisely, the water equivalent of snow, a measure of the amount of water that will be released when the snowpack melts) is in the 30th percentile or less of the historical peak.

Using these definitions, California could experience episodic light to zero snow as early as the late 2040s and persistent low to zero snowfall into the 2060s according to a high-resolution climate projection. For other parts of the western United States, persistent low to no snow emerges in the 2070s. The authors caution the need for more analysis with a broader set of climate projections to strengthen confidence in the timing of the emergence of light to no snow conditions.

The authors describe the climate projections in their study, writing: “In the mid to late 21st century, a growing fraction of the western United States is affected by snow-water equivalent deficits relative to the historical period. In particular, only 8 to 14% of years are classified as little or no snow over the period 1950-2000, compared to 78 to 94% over 2050-2099. In all regions, an abrupt transition occurs between the middle and the end of the 21st century. “


These computer-generated images show data for the lowest (left) and highest snowpack conditions over a 36-year period. (Use the mouse to move the cursor.) An algorithm generated each point on the map, comparing data from 1982 to 2017 and using the lowest or highest values. Since individual years can result in an abnormal snowpack in one mountain region and not another, these images convey composites of low and high snow conditions regardless of the year of occurrence. (Credit: Images generated by Ben Hatchett and Alan Rhoades / Berkeley Lab, using data from Zeng, X., P. Broxton, and N. Dawson. 2018. Snowpack Change From 1982 to 2016 Over Conterminous United States, Geophysical Research Letters. 45 12940-12947)

Impacts on water resources

The impacts of a future with little or no snow extend beyond simply reducing flow, although this is certainly an important consequence. In the Sierra Nevada, for example, the amount of water in the snowpack on a typical April 1 is nearly double the surface storage of the reservoir in California.

“A snow-free future has huge implications for where and when water is stored in the western United States,” said Siirila-Woodburn. “In addition to the direct impacts on recreation and the like, there are a lot of side effects on natural and managed systems, from a hydrologic perspective. So it’s everything from an increase in the frequency of forest fires to changes in ground and surface water patterns and changes in the type and density of vegetation.

With less snow and more rain, groundwater levels in mountain systems can be affected because snowmelt seeps underground more efficiently than precipitation. In addition, less snow at lower elevations will reduce the overall area of ​​the snowpack stored in the mountains, which could result in less available snowmelt seeping into the ground.

Now for the good news …

The aim of the authors in carrying out this study was to stimulate reflection on coping strategies. “We want society to be proactive in dealing with these changes in the snowpack rather than reactive,” said Rhoades. “Our hope in presenting the synthesis of the light to no snow literature is to be able to understand the problem in a ‘one-stop-shop’ manner. Additionally, we have highlighted new climate adaptation strategies emerging from non-traditional partnerships with universities and water agencies, which will be key parts of a portfolio of adaptation approaches needed to overcome the loss of snow in a warmer world.

One of these partnerships is a project supported by the Ministry of Energy called HyperFACETS, which involves 11 research institutes, including Berkeley Lab, working with water utility managers in California, Colorado, Florida and Pennsylvania.

The paper also discusses potential adaptation strategies, such as a technique known as managed recharge of aquifers, in which excess surface water is stored underground as groundwater for later use. . Another relatively new technique, forecast-based reservoir operations, in which meteorological and hydrological forecasts are used to inform decisions about the retention or release of water from reservoirs, has been recently shown to increase water storage at Lake Mendocino in California by 33%.

These and other techniques hold promise for increasing water supply, but the authors also recommend greater collaboration, both among scientists and within society as a whole, to expand the portfolio of strategies for adaptation to climate.

“We champion the idea of ​​engagement with best scientific practices and of increased collaboration or partnership between researchers and stakeholders. For example, city directors are concerned with flood control; farmers are concerned about water storage; each has its own goals. Even within science, the disciplines are generally siled, ”said Siirila-Woodburn. “If everyone worked together to manage water rather than working independently for their own purposes, there would be more water for everyone. “

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Founded in 1931 on the conviction that the greatest scientific challenges are best met by teams, Lawrence Berkeley National Laboratory and its scientists have received 14 Nobel Prizes. Today, researchers at the Berkeley Lab are developing sustainable energy and environmental solutions, creating useful new materials, pushing the boundaries of computing, and probing the mysteries of life, matter, and the universe. Scientists around the world rely on the laboratory facilities for their own scientific discoveries. Berkeley Lab is a national multi-program laboratory, operated by the University of California for the Office of Science, US Department of Energy.

The DOE’s Office of Science is the largest supporter of basic research in the physical sciences in the United States and works to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

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