Evaluation of Potential Climate Change Impacts on Salmonid Populations in the Chehalis River, Washington

The effect of future climate on coho, fall and spring Chinook and steelhead was analyzed in the Chehalis Basin, a rain-driven system with high winter flows and dry, warm summers. Projections call for increased winter rainfall, stronger storms and warmer summer temperatures. To understand the potential impacts of altered climate, the capability of stream habitat to support anadromous salmonids under current conditions was compared to that under low and high alternative conditions consistent with projections of future climate.  A life cycle habitat model, Ecosystem Diagnosis & Treatment (EDT3) evaluated habitat potential by sub-watershed. The alternative conditions were constructed from historical flows and temperatures consistent with projections of increased winter precipitation and warmer summer temperatures.  Habitat potential for all species was severely reduced under the alternative conditions.  Spring Chinook were most impacted and fall Chinook the least impacted. Distribution of salmon across the basin was constricted; less productive sub-populations were eliminated.  With high climate change, habitat potential for spring Chinook was eliminated extirpating the population. Life history diversity was reduced resulting in less-resilient fish populations.  The analysis demonstrated potentially significant implications of climate change for fisheries planning and the utility of habitat models to provide insight into climate change impacts.