MOUNT VERNON, Wash. – As glaciers in the North Cascades and other areas of the Pacific Northwest continue to melt, the streams they typically replenish during the summer will get less water in August and September in coming decades.
A study recently published in Water Resources Research, a journal of the American Geophysical Union, underscores this issue in the Skagit River watershed and other areas of the Cascade and Olympic mountains.
The study found that with a decline in snowpack accumulation and summer melt from some glaciers, some areas in the region could see 80 percent lower summer streamflows by the end of the century, according to a news release.
Snow and ice accumulates in the North Cascades and other mountainous areas each winter and melts a bit each summer. That annual cycle provides water used for drinking, irrigation and hydroelectric power generation in the state.
That water is also critical for salmon, which rely on cold, clean streams for survival.
Christopher Frans, lead author of the study, said less glacier melt in the Skagit River watershed over time will impact dams, salmon, communities that use the river as a water source and farms that rely on the river for irrigation.
“With a warming climate, there are likely to be significant changes to streamflow volumes and timing due to changes in snow and ice in the upper basin,” he said. “Losses of glacier melt and its contribution during the low-flow season will impact the systems that have historically relied on this consistent source of streamflow.”
The new study uses a model to evaluate how decreasing snowpack and shrinking glaciers could impact stream flows in the region through 2099.
The model showed that summer melt from some lower elevation glaciers is already declining, and summer melt from some higher elevation glaciers is expected to begin declining by 2050, according to the study.
The study focused on six stream basins in the Pacific Northwest, including for the Cascade River, Thunder Creek, Stehekin River, Nisqually River, Hoh River and Hood River.
Thunder Creek, which flows into Diablo Lake, and Cascade, which flows into the Cascade River, are within the Skagit River watershed.
The model showed that since 1960, those basins have received a significant amount of glacial melt in September. During that month, an average of 15 percent of the Cascade River and 28 percent of Thunder Creek is from glacial melt, Frans said.
The model also showed that glaciers – including in the Thunder Creek basin – could nearly disappear by 2100 if greenhouse gas emissions are not curbed.
Thunder Creek and the Cascade River were selected for the study largely because they are home to some of the most heavily monitored glaciers in the region, Frans said.
In the Thunder Creek basin, National Park Service geologist Jon Riedel documents the accumulation and melt of ice at North Klawatti Glacier each year. In the Cascade River basin, the U.S. Geological Survey monitors the South Cascade glacier.
The data from those glaciers and others studied by Riedel in the Olympics and at Mount Rainier helped to ensure the model used for Frans’ study accurately represented changes in the glaciers.
“By and large his model reproduced reality, which is the first step to looking into the future,” Riedel said.
Riedel, who was also a co-author of the study, said when it comes to the Cascade River and Thunder Creek basins, they’re two of five major glacier valleys in the greater Skagit River watershed.
What the model showed for the Cascade River and Thunder Creek basins – and the Pacific Northwest region as a whole – does not bode well for the Skagit River watershed and those who rely on it for water.
“Our summer water resources in Skagit Valley will continue to be impacted as the glaciers recede,” Riedel said. “It (the Skagit River watershed) will go from one of the most glaciated basins in the lower 48 to one of diminished streamflow in September. That’s important to us.”
Glaciers throughout the Pacific Northwest have been shrinking since the 1980s due to warming temperatures, according to the study. Those in the North Cascades are about half the size they were a century ago.
Changes in glacial melt combined with changes in how much precipitation falls as snow and rain have already resulted in an overall decrease in stream flows throughout the region, according to the study.
Riedel documented that in the Skagit River basin in a previous study, published in 2016 based on his work for the National Park Service and USGS data.
“Water resources are already being taxed,” he said. “We’re losing water as the glaciers melt.”
Riedel said the new study paves the way for more research using the model Frans created.
NASA and Seattle City Light provided funding for the study.