Back-to-back low-snow years ‘highly likely’ for Idaho in 2050s. What that means

Idahoans rely on snow for skiing, fishing, agriculture and more. But new research predicts that Idaho will get more back-to-back poor snow years, threatening the snow we enjoy and water we need.

“Today’s low-snow years will become the average by the middle of the century,” said John Abatzoglou, an associate professor in geography at the University of Idaho. “We still expect some large snow years, but they will become increasingly rare.”

Using historical data, four researchers, including three from the U of I, simulated snow pack data in 2050-2079 across the Western U.S. under a high greenhouse-gas emission scenario. This is the greenhouse gas emissions scenario Earth is on track for if “business as usual” continues, according to the Intergovernmental Panel on Climate Change.

The simulation predicts that average global temperature will increase almost 9 degrees Fahrenheit.

“We classified a low snow year as the bottom 25% of historic snow pack,” Abatzoglou said in an interview. “Historically low snow years have a 6-7% chance of happening each year. Our data shows a jump to 42% chance each year in mid-century.”

In this 2015 photo, the snow is nearly gone on the Trinity Mountains in the Boise National Forest. With more back-to-back low snow years, the Treasure Valley’s “fourth reservoir” – as farmers call the snowpack – will provide less water. Bureau of Reclamation

One low snow year can hurt ski resorts, wildfire and water availability. Back-to-back low snow years can have more severe effects.

“This matters, because it is like drawing down a bank account without replenishing,” said Adrienne Marshall, postdoctoral fellow at the University of Idaho and lead author of the study. “Those multiple years without replenishing the snow have compounding effects.”

According to Abatzoglou, some of those effects include “detrimental effects for low elevation ski resorts” and ecological implications for wild animals like moose and wolverine that use deep snow to breed and escape predators.

The timing and amount of water in spring runoff is also expected to change.

“We know the amount of Idaho snow is declining,” said Timothy Link, a hydrology professor at the University of Idaho. “But we show there will be variability in the maximum snow pack and variability in the timing of spring runoff too.”

Most Idaho water users like farmers, boaters and anglers depend on reservoir releases, especially during the late summer.

“The Boise River is more sensitive and will be impacted by variable snow pack timing,” Link said.

The South Fork of the Boise River, just below Anderson Ranch Dam, could see more variable water flows by mid-century. Mike Prater mprater@idahostatesman.com

The Bureau of Reclamation is considering raising the Anderson Ranch dam on the south fork of the Boise River by 6 feet, increasing water storage by approximately 29,000 acre feet, in an effort to supply the growing Treasure Valley and adjust for future variable water availability. One acre-foot is about 326,000 gallons (1.2 million liters).

“Most water managers use April 1 as the date of maximum snow pack,” Abatzoglou said. “With climate change, that max date of snow pack will shift earlier in the year. April 1, the magical number that determines water managers’ decisions, will become unreliable.”

The researchers hope their work will help water managers better manage for future variability.

“This is one piece of the picture of how climate change will affect forests and water in Idaho,” Marshall said. “We know future western water will be different.”

Rachel Hager is writing for the Idaho Statesman this summer on a fellowship through the American Association for the Advancement of Science. She is a master’s student in ecology at Utah State University and earned a bachelor’s degree in biology at Bryn Mawr College.