Home Career Limiting global warming can now save a precious freshwater resource — ScienceDaily

Limiting global warming can now save a precious freshwater resource — ScienceDaily


Snow-capped mountains don’t just look majestic – they’re vital to a fragile ecosystem that’s existed for tens of thousands of years. Mountain runoff and snowmelt flow into streams, rivers, lakes, and oceans—and today, about a quarter of the world depends on these natural “water towers” to recharge downstream reservoirs and underground aquifers for urban water supply, agricultural irrigation, and ecosystem support .

But this precious freshwater resource is under threat of extinction. The planet is now about 1.1 degrees Celsius (1.9 degrees Fahrenheit) warmer than pre-industrial levels, and mountain snowpack is shrinking. Last year, a study led by Alan Rhodes and Erika Cyrillo-Woodburn, research scientists in Earth and Environmental Sciences at the Lawrence Berkeley National Laboratory (Berkeley Lab), showed that if global warming continues under a high-emissions scenario, low Snowless winters will become commonplace in the western US mountain ranges in 35-60 years.

Now, in a recent study in Nature Climate Change, a research team led by Rowdes found that if global warming reaches about 2.5 degrees Celsius compared to pre-industrial levels, mountain ranges in the southern mid-latitudes, particularly the Andes region of Chile, will face future from low to no snow between 2046 and 2051 – or 20 years earlier than mountain ranges in the northern mid-latitudes, such as the Sierra Nevada or the Rockies. (Maximum snow or no snow occurs when the annual maximum of water storage in the form of snowpack is in the bottom 30% of historical conditions for a decade or more.) The researchers also found that low to no snow conditions will occur in southern middle latitudes for a third of the warming than in northern middle latitudes.

“These findings are very shocking. We hypothesized that both regions in the southern and northern hemispheres would respond similarly to climate change and that the Andes would be more resilient given their high elevation,” said Alan Rhodes, a hydroclimate researcher at Berkeley Lab. in Earth and Environmental Sciences and lead author of the new study. “This shows that not every degree of warming has the same effect in one region than another.”

In another important finding, the researchers learned that this low-snowfall future coincides with about 10% less mountain runoff in both hemispheres, in wet and dry years.

“If you expect 10% less runoff, that means at least 10% less water is available each year to fill reservoirs during the summer months when agriculture and mountain ecosystems need it most,” Rhodes said.

Such reduced runoff would be particularly devastating to agricultural regions already suffering from years of drought.

California’s current drought is entering its fourth year. More than 94 percent of the state is in severe, extreme or exceptional drought, according to the US Drought Monitor. Statewide depletion of groundwater supplies and municipal wells is severely affecting the San Joaquin Valley, the state’s agricultural heartland.

And Chile, which exports about 30% of its fresh fruit each year, much of it to the United States, is in the midst of a historic 13-year drought.

Saving snow, fresh water by curbing greenhouse gas emissions

But the new study also shows that both the northern and southern mid-latitude mountain ranges could be prevented from experiencing snow if global warming is limited to essentially 2.5 degrees Celsius (4.5 degrees Fahrenheit), researchers say.

Their analysis is based on Earth system models that simulate different climate components, such as the atmosphere and the land surface, to determine how mountain water cycles may continue to change through the 21str century, and what levels of warming could lead to a widespread and sustainable future with little or no snow in the American Cordillera, a chain of mountain ranges spanning the western “ridge” of North America, Central America, and South America.

The researchers used the computing resources of Berkeley Lab’s National Energy Research Computing Center (NERSC) to process and analyze data collected by climate researchers from around the world through the Department of Energy’s CASCADE (Calibrated and Systematic Characterization, Attribution, and Extreme Value Detection). project. (Data after study analysis are available to the NERSC research community.)

The closest that Rhoads and his team came to what Rhodes and his team considered “episodic low-to-no-snow conditions” were in California between 2012 and 2016. The lack of snow and drought in recent years have demonstrated the vulnerability of our water supply and, in part, led to the passage of the California Sustainable Groundwater Management Act, new approaches to water and agricultural management practices, and mandatory water shutoffs, Rhoads said.

Persistent snow (10 years in a row) has ranged from low to no snow, but Rhodes said water managers are already thinking about that future. “They are working with scientists to develop strategies for proactive rather than reactive water management for worst-case scenarios where we cannot reduce greenhouse gas emissions to avoid certain levels of warming. But a better strategy would be to prevent further warming by reducing greenhouse gas emissions,” he said.

For future research, Rhodes plans to continue studying and run even higher-resolution simulations of the new Earth system model “to give more spatial context of when and where snow loss can occur and what’s causing it,” he said, and explore how each The degree of warming may change other key drivers of the mountain-water cycle, such as the location and intensity of atmospheric rivers, as well as the responses of mountain ecosystems.

He also plans to continue working with water managers through the Department of Energy-funded HyperFACETS project to identify ways we can better prepare for a future with little or no snow through new management strategies such as strengthening drought infrastructure and flood and managed aquifer. recharge.

Rhoades is optimistic, citing a Berkeley Lab-led study that found that achieving zero carbon emissions from energy and industry by 2050 could be achieved by retooling the US energy infrastructure to run mostly on renewable energy.

“All it takes is the will and initiative to invest financial resources with the level of urgency that climate change requires, so we need to start doing it today,” he said.

Researchers from the Desert Studies Institute in Reno, Nevada; UC Berkeley; UC Davis; California State University, Long Beach; UC Irvine; National Center for Atmospheric Research; and Pennsylvania State University participated in the study.

The work was supported by the Department of Energy’s Office of Science and the Department of Energy’s Office of Biological and Environmental Research.

NERSC is the Department of Energy’s Office of Science User Facility at Berkeley Lab.

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