Winter Stream Temperature Response to Shifting Snow Regimes in Forested Headwater Catchments, and Bioenergetic Implications for Cutthroat Trout (Oncorhynchus clarkii)

The majority of research linking stream thermal regimes to fish biology and ecology, and the potential impacts of climatic warming, has focused on summer due to concerns about negative impacts associated with exceedance of thermal tolerances. However, relatively small but persistent changes in winter temperatures could have significant effects on salmonid growth rates. The objective of this study was to use a process-based hydrology/temperature model to explore the effects of climatic warming on headwater stream thermal regimes in the rain-on-snow zone of the Pacific Northwest, and then to use a bioenergetics model to estimate the associated impacts on trout growth. The study focused on East Creek, a forested headwater catchment located in the transient snow zone. Model results suggest that the duration of snow cover is highly sensitive to winter air temperatures, and that reduced snow cover acts together with increased rain temperatures to cause higher winter stream temperature, due to the increased temperature of lateral hillslope discharge to the stream channel. The effects of temperature changes on trout growth were highly sensitive to assumptions about food availability, which represents a major source of uncertainty for making projections about the potential effects of future climate change.