Rising temperatures will reduce the peak snowpack in the Cascades slopes east of Eugene, Ore. by more than fifty percent, according to a climate study Oregon State University researchers published Thursday.
Climate models from the Intergovernmental Panel on Climate Change predict temperatures in the Pacific Northwest will rise about 3.6 degrees by the mid-century. That projected increase matters in the western Cascades, where a few degrees is often the difference between a snowy day and a rainy day.
Oregon State University Researcher Eric Sproles developed a sensitive model to predict how that temperature increase will affect the McKenzie River, which starts near Mount Washington and is a major tributary of the Willamette.
Sproles says the McKenzie River serves as a good representative example of a Cascades watershed, and that the river had a good historic record he could use to refine climate modes: 21 years of past data on snowpack, temperatures, and water levels.
Sproles found that climate change won’t affect the total amount of precipitation much. But it will reduce the snowpack that feeds the river in the spring and summer by 56 percent.
“The loss of snowpack is going to be 2.5 times bigger than the largest reservoirs that are in the basin right now,” he says.
Researchers with the University of Washington’s Climate Impact Group have modeled similar changes in the snowpack in the Washington cascades, with implications for rivers like the Columbia and Yakima.
Lara Whitely Binder, an outreach specialist with the Climate Impact Group, says numerous studies have predicted reductions in snowpack at moderate elevations, decreased summer flows in snowpack dominated river basins on the west side, and changes in the timing of peak flows in Northwest rivers.
“There’s a consistent story line emerging from these studies. It increases the robustness of the science,” she says. “For people working in the central Oregon area, it’s always helpful to have a study that relates to the watershed you’re working in.”
More than 200,000 people, including Eugene residents, depend on the McKenzie for drinking water, according to the McKenzie River Watershed Council.
The Willamette tributary also supports agriculture and salmon runs.
Sproles says he hopes his study can be used as a tool to help plan for the future:
“This is not a doom and gloom story; it’s more of a cautionary tale. We do not live in a precipitation limited environment by any means. The shifts in precipitation will be expressed in streamflow, but we’re fortunate. We have water. But we might have to change our decisions in how we use that water, especially the timing.”
OPB | Feb. 22, 2017