New study says climate change behind drop in Northern Hemisphere snowpack
Glacier peaks A view of glacier-clad peaks in Washington’s North Cascades. (Bill Lucia/Washington State Standard)
New scientific research shows that human-caused climate change is putting the most densely populated areas of the Northern Hemisphere, including the American West, at risk of losing vast portions of their water supply because of decreasing snowpack.
Published in the journal Nature, the report led by two Dartmouth College researchers found climate change-driven snowpack trends in half of the 169 river basins in the Northern Hemisphere, 31 of which they said they could “confidently attribute to human influence.”
“Together, our findings portend serious water-availability challenges in basins where snowmelt runoff constitutes a major component of the water supply portfolio,” the researchers wrote in their conclusion. “Improving our understanding of where and how climate change has and will affect snow water resources is vital to informing the difficult water resource management decisions that a less snowy future will require.”
The researchers built a model that analyzed observations and models of snowpack, temperature, precipitation, and runoff data from 1981 through 2020, then used the uncertainties from the models and observations to try to cut through temperature and precipitation variations and account for regional differences to see how a warmer planet would affect snowpack and runoff in the future.
Those models, they wrote, allowed them to produce more than 12,000 estimates of the effects of human-caused climate change on March snowpack across the Northern Hemisphere.
The researchers said that better understanding the unknowns in analyzing snowpack, and how human-cause climate change is affecting the snowpack in general, can lead to better climate models and also better policymaking for governments and water managers who will have to deal with the effects of the reduced runoff in the future.
“It means that water managers who rely on snowmelt can’t wait for all the observations to agree on snow loss before they prepare for permanent changes to water supplies. By then, it’s too late,” Dartmouth’s Justin Makin, the senior author of the paper and an associate professor of geography, said in a statement. “Once a basin has fallen off that cliff, it’s no longer about managing a short-term emergency until the next big snow. Instead, they will be adapting to permanent changes to water availability.”
One of the keys in being able to account for uncertainties and still make predictions, according to the paper, was identifying -8 degrees Celsius, or 17.6 degrees Fahrenheit, as the average winter temperature where snowpack can start to decrease rapidly with minimal air temperature increases.
The authors found that below that temperature threshold, warmer temperatures have little effect on snowpack. But for each 1 degree Celsius that temperatures go above the threshold, accelerated losses in snowpack result.
Those regions below the temperature threshold are generally along or north of 60 degrees latitude, in the northern reaches of Alaska, Canada and Asia. But they account for about 80% of March snowpack in the Northern Hemisphere, according to the paper.
However, the researchers wrote, the remaining 20% of the snowpack primarily sits just above the temperature threshold, making it prone to what the researchers called a “snow-loss cliff,” where each degree of warming, on average, during the winter, will have a broader effect on the snowpack and water retention.
“Such a relationship suggests that further warming and thus additional time spent beyond this −8 °C threshold will homogenize snow trends towards more consistent declines, portending widespread and accelerating snow losses for many basins over the coming decades,” the paper says.
That 20% area of the hemisphere that is just on the edge of the “cliff” also happens to include about 80% of the people that live in the Northern Hemisphere, according to the paper.
“As such, further warming is likely to have rapidly emerging impacts on snow water resources in the mid-latitude basins where people reside and place competing demands on fresh water,” the researchers wrote.
The researchers said their models both uncovered human-caused snow-water equivalent declines in some areas where observations had shown increases during the past 40 years, like the Columbia River basin, but also signs that steep decreases could be in store for other parts of the West.
The paper said the Upper Mississippi River basin, which starts in Montana, could see a 30% decline in spring runoff, and the Columbia River basin could see a 33% decline. Those two basins are home to 90 million people, according to the paper. The researchers found the Colorado River basin, home to 14 million people, could see a runoff decline of 42%.
The declining snowpack and runoff would in turn affect several facets of the economy, from winter recreation, which brings in millions to Western states each year, to agriculture, water recreation, and land management.
“We’ll likely see further consolidation of skiing into large, well-resourced resorts at the expense of small and medium-sized ski areas that have such crucial local economic and cultural values,” Mankin said in a statement from Dartmouth. “This will just accelerate, making the business model inviable.”
This article first appeared in the Daily Montanan, which, like the Oregon Capital Chronicle, is part of States Newsroom, a network of news bureaus supported by grants and a coalition of donors as a 501c(3) public charity. Daily Montanan maintains editorial independence. Contact Editor Darrell Ehrlick for questions: [email protected]. Follow Daily Montanan on Facebook and Twitter.
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