Limiting global warming now can preserve a precious freshwater resource

Newswise – Snow-capped mountains aren’t just majestic – they’re vital to a delicate ecosystem that’s been around for tens of thousands of years. Mountain water runoff and snowmelt flow into streams, rivers, lakes and oceans – and today around a quarter of the world depends on these natural “water towers” to replenish downstream reservoirs and underground aquifers for city water supply, agricultural irrigation and ecosystem support.

But this precious freshwater resource is in danger of disappearing. The planet is now about 1.1 degrees Celsius (1.9 degrees Fahrenheit) warmer than pre-industrial levels, and mountain snowpacks are decreasing. Last year, a study co-led by Alan Rhoades and Erica Siirila-Woodburn, earth and environmental science researchers at Lawrence Berkeley National Laboratory (Berkeley Lab), found that if global warming continues under the high emissions scenario, winters with little or no snowfall will become common in the western US mountain ranges in the next 35 to 60 years.

Now in a recent Natural climate change study, a research team led by Rhoades found that if global warming reaches about 2.5 degrees Celsius above pre-industrial levels, mountain ranges in the mid-latitudes of the south, the Andean region of Chile in particular, will face low to zero future snow between the years 2046 and 2051 – 20 years earlier than mid-northern latitude mountain ranges such as the Sierra Nevada or the Rocky Mountains. (Light to no snow occurs when the annual maximum of water stored as snow is in the lower 30% of historical conditions for a decade or more.) The researchers also found that light to no snow conditions would appear in southern mid-latitudes at one-third the warming relative to northern mid-latitudes.

“These findings are quite shocking. We assumed that both regions of the southern and northern hemispheres would react similarly to climate change and that the Andes would be more resilient given their high altitude,” said Alan Rhoades, a hydroclimatology researcher in Berkeley Lab’s Earth and Environmental Sciences and lead author of the new study. “It shows that not all degrees of warming have the same effect in one region as in another.”

In another major finding, researchers learned that such a low-to-no snowfall future coincides with about 10% less runoff from mountains in both hemispheres, in both wet and dry years.

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

Such a decrease in runoff would be particularly devastating for agricultural regions already parched by multi-year droughts.

The current drought in California is entering its fourth year. According to the US Drought Monitor, more than 94% of the state is experiencing severe, extreme, or exceptional drought.. Dwindling groundwater supplies and municipal wells across the state are having a severe impact on the San Joaquin Valley, the agricultural heartland of the state.

And Chile – which exports around 30% of its fresh fruit production each year, much of which is shipped to the United States – is in the midst of a crisis. historic 13-year drought.

Save snow and fresh water by limiting greenhouse gas emissions

But the new study also suggests that little to no snow in mid-latitude northern and southern mountain ranges can be avoided if global warming is limited to essentially 2.5 degrees Celsius (4.5 degrees Fahrenheit), the researchers said. researchers.

“Preventing a future of little or no snow in the northern or southern hemisphere depends on keeping global warming to no more than 2.5 degrees Celsius,” Rhoades said.

Their analysis is based on Earth system models that simulate the different components of climate, such as the atmosphere and land surface, to identify how mountain water cycles could continue to change during the 21st century, and what levels of warming could result in a widespread and persistent future of little to no snowfall in the Cordillera America – a range of mountain ranges spanning the western “backbone” of North America, America Central and South America.

The researchers used Berkeley Lab computing resources National Energy Research Computing Center (NERSC) process and analyze data collected by climatologists around the world through the Ministry of Energy CASCADE (Calibrated and systematic characterization, attribution and detection of extremes) project. (Post-analysis data from the study is available to the NERSC research community.)

The conditions closest to what Rhoades and his team considered “episodic light to no snow” conditions occurred in California between 2012 and 2016. The light snow and dry conditions in those years demonstrated the vulnerability of our water supply and, in part, led to the death of the California Sustainable Groundwater Management Actnew approaches to water and agricultural management practices and mandatory water shut-offs, Rhoades said

Persistent low-to-none snowfall (10 consecutive years) has yet to happen, but Rhoades said water managers are already considering such a future. “They are collaborating with scientists to come up with proactive rather than reactive water resource management strategies for worst-case scenarios if we cannot mitigate greenhouse gas emissions to avoid certain levels of warming. But the best strategy would be to prevent further warming by reducing greenhouse gas emissions,” he said.

For future studies, Rhoades plans to continue to examine and run new Earth system model simulations at even higher resolution “to give more spatial context of when and where snow loss might occur.” and what’s causing it,” he said, and studying how each degree of warming could alter other key factors of the mountain water cycle, such as landing location and intensity. of atmospheric riversand responses of mountain ecosystems.

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

Rhoades is optimistic, citing research from another study led by the Berkeley lab that found it is possible to achieve net zero carbon dioxide emissions from energy and industry by 2050. rebuilding America’s energy infrastructure to run primarily on renewable energy.

“It just requires the will and the initiative to invest financial resources at the level of urgency demanded by climate change, which means we need to start doing it today,” he said.

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

The work was supported by the DOE Office of Science and the DOE Office of Biological and Environmental Research.

NERSC is a user facility of the DOE Office of Science at the Berkeley Laboratory.

Founded in 1931 on the belief that the greatest scientific challenges are best met by teams, Lawrence Berkeley National Laboratory and its scientists have been awarded 16 Nobel Prizes. Today, Berkeley Lab researchers 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 facilities of the laboratory for their own scientific discovery. Berkeley Lab is a multi-program national laboratory, operated by the University of California for the US Department of Energy’s Office of Science.

The DOE’s Office of Science is the largest supporter of basic physical science research 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.

Teresa H. Sadler