The Pacific Northwest’s mountainous snow, kept frozen in high elevations, was thought to be resilient to bursts of warmth in the springtime. But this durability may be weakening, threatening a key source of the region’s water supply, according to a study released last week.
Researchers in Washington State University’s School of the Environment intended to assess how the 2021 heat dome influenced snowpack. Instead, the study revealed an alarming warming trend that began well before the extreme event, said lead author Luke Gilbert Reyes, a doctoral student at WSU Vancouver.
“This is relatively new and underappreciated,” he said. “Hopefully, it can be a more fruitful line of research … in the future.”
Washington’s reservoirs and natural waterways rely on snowmelt through the summer. Less snowmelt and runoff have a wide-reaching domino effect, thwarting healthy freshwater habitats, agriculture and recreation, according to the National Oceanic and Atmospheric Administration’s Climate Prediction Center.
In late June 2021, the Pacific Northwest was engulfed in a rare heat dome — a pocket of trapped hot ocean air — that pushed temperatures to a record-breaking 122 degrees. (Vancouver reached an all-time high of 115 degrees June 28, 2021, at Pearson Field.)
To review the heat dome’s effect on snowmelt, Reyes and co-author Marc Kramer used a modeling and data system that tracks snow cover, depth and snow water equivalents at multiple stations throughout the region. Unexpectedly, data sets showed that snowpack in the Olympic and Cascade Mountains had significantly melted by the time the heat dome arrived.
A series of heat waves, ranging between 7.2 and 12.6 degrees above normal, drifted across the region through April and early June in 2021, causing high-elevation snow to melt. However, early warming trends began decades ago, suggesting heat waves are becoming more frequent and intense, Reyes said.
When looking at data between 1940 and 2021, researchers found the number of springtime heat waves doubled since the mid-1990s.
Climate change impacts on snowpack have historically been based on April 1 snow levels and average monthly temperatures. This skews averages, as data might show single-degree temperature changes but don’t accurately relay the “profound” impact a few days of intense heat have on snow, Reyes said.
Both the heat dome and heat waves in 2021 melted snowpack three weeks earlier than expected. That same year, La Niña brought above average snowpack to the Pacific Northwest. But this cover, which would normally last into August, disappeared by late June.
The coming year doesn’t provide much cooling relief for snowpack, either.
“We have a coming El Niño year and next year, and there may be some amplification effects,” Kramer said in a WSU Insider release. “If we have less snow to begin with, the snowpack is going to be all that much more vulnerable to these heat anomalies earlier in the season.”
El Niño is a deviation from normal weather patterns, blanketing the northern United States and Canada in dry and warm conditions, while the southern U.S. experiences wetter weather. The weather pattern will likely result in decreased runoff and summer water availability, Kramer said.
Although a series of atmospheric rivers in early December improved most of the Pacific Northwest’s drought conditions, snowpack remains below average in most basins, said Nick Siler, Oregon’s assistant climatologist. El Niño’s warm conditions only worsen the situation.
“There’s an elevated risk of snow drought independent of what happens to precipitation,” he said during a Monday climate outlook webinar hosted by the National Integrated Drought Information System, the Northwest Climate Hub and the Oregon Climate Change Research Institute.
