Early season snowmelt could bring the West summer water scarcity: study

Climate change is expediting spring snowmelt and replacing snow with rainfall in the Mountain West — making an already arid region increasingly at risk of summer water scarcity, a new study has found.

From 1950 to 2013, the amount of water stored in snowpack plunged in more than 25 percent of the mountainous areas of the Western North America, according to the study, published on Monday in Nature Communications Earth & Environment.

This decline has occurred in part because more snow is melting during winter and spring, blurring the boundaries between seasons, per the study.

“On average and in every mountainous region that we looked at, snow melt is occurring closer in time to when it fell,” lead author Kate Hale, who conducted the research as a University of Colorado Boulder graduate student, said in a statement.

“The timing of water availability is shifting toward earlier in the springtime, with less snow melt and water availability later in the summertime,” added Hale, who is now a postdoctoral associate at the University of Vermont.

The Western U.S. and Canada rely on snow for most of their water — meaning that the Rocky Mountains, the Sierra Nevadas and other mountain ranges have essentially served as “water towers” for this region, according to the authors.

By storing water throughout the winter, the mountains provide water, via snowmelt, in spring and summer, the researchers stated.

State and regional water managers use a metric known as snow water equivalent — the amount of water contained in snow — every April 1 to forecast water availability for that year, Hale explained.

But Hale and her colleagues felt that having just the April 1 snapshot was insufficient, as it doesn’t demonstrate whether snow slowly accumulated over the previous six months or if it fell in one lump sum just days prior to the measurement.

To broaden their understanding, the researchers used two publicly available data sources to develop a new measurement called the “snow storage index.”

This index incorporates both the timing and the amount of snowfall, as well as snowmelt, before and after April 1, according to the study.

“The snow storage index allows us to look at snow water storage, not just in the context of how much is there at any given time, but the duration of that storage on the ground,” senior author Noah Molotch, an associate professor of geography at the University of Colorado Boulder, said in a statement.

High scores on the snow storage index — a number as close to 1.0 as possible — occurred in places where snowfall is very seasonal, such as in the Cascades, the researchers found.

But in Colorado’s Rocky Mountains, the scores were lower — between 0 and 0.5 — indicating that snow both accumulates and melts throughout the colder half of the year, according to the study.

The good news, however, is that because the Rockies and Colorado’s Front Range are already used to enduring an alternating pattern of snowfall and snowmelt during winter and spring, the region might adapt easier to shifts in snowpack storage, the authors noted.

Nonetheless, they warned that the mountain regions of the West Coast, which are highly dependent on snowpack meltwater in spring and summer, could endure “a painful adjustment.”

“The snowpack is eroding and disappearing before our eyes,” Molotch said.

That’s going to present challenges in terms of managing the infrastructure that’s allowed the Western United States to flourish over the last 100 years,” he added.

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