Early snowmelt in Western Canada and the U.S. mountain ranges is causing drier summers and increasing wildfire risk.
Mountain snowpacks act as a natural reservoir for storing winter precipitation until summer months when downstream water demand is greatest. In the past, snowmelt usually began in late May or early June, thereby helping to sustain water requirements for downstream needs.
However, climate change has been thawing the snowpack much earlier, sometimes as early as March in some regions, and replacing snow with rainfall, according to CTV News Canada.
This early thawing and increased precipitation is making an already arid region increasingly at risk of summer water scarcity, a new study from the University of Colorado Boulder has found.
From 1950 to 2013, the amount of water stored in snowpack plunged in more than 25 percent of the mountainous areas of Western North America, according to the study, published in the journal Nature Communications Earth & Environment.
This is happening – in part – because more snow is melting during winter and spring, blurring the boundaries between seasons, per the study. This means there will be less water available for later in the year when it is needed.
“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, reports The Hill.
“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.
A new metric called the Snow Storage Index (SSI)
States and regional water managers use the “snow water equivalent” on April 1 every year to determine the amount of water contained in snow, enabling them to forecast water availability for the coming year.
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.
So, using two publicly available data sources, they set about creating a Snow Storage Index (SSI), that 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. 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.
The study also found that the mountain ranges along North America’s western 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.
