The Response of the Stillaguamish Watershed to Projected Climate Change

Archived video of this presentation.

The Stillaguamish Watershed is typical of many watersheds in the Puget Sound region—it has high relief that maintains a winter snowpack above about 1000 meters in elevation. Historically, accumulated snow in the watershed melts out by late spring or early summer, sustaining streamflows and serving as a cool-water buffer for salmon habitat.  Modeling of projected warming climates in the Stillaguamish basin indicates that warmer winter temperatures will produce more rain than snow causing snowlines to retreat to higher elevations and an overall decline in basin winter snowpack. The transition to a rain-dominated basin results in a projected 25% increase in winter peak flows, increasing the risk to lowland infrastructure and salmon restoration efforts. A reduced snowpack also results in lower spring and summer streamflows and an increase in stream-water temperatures, which stresses salmon—further threatening their recovery as a species.