Implications of Changing Climate for Stream Temperature and Fish Growth Potential in Snow-Influenced Watershed

Abstract:

The Snoqualmie River Basin (SRB) is a snow-influenced watershed where snowmelt cools down the summer water temperature. It is also home to Endangered Species Act (ESA) protected salmon and steelhead, and substantial cold-water resident fish populations. Climate projections in the SRB suggest higher air temperature, less snow accumulation, and earlier snowmelt; these changes are expected to reduce summertime streamflow and exacerbate warming in rivers where a warming trend has already been observed. The goal of this study is to provide a process-based understanding of climate change impacts on stream temperature and cold-water habitats, which can be used to develop plausible management scenarios of riparian vegetation and land use to mitigate the impacts. Here, we used an integrated Distributed Hydrology Soil Vegetation Model (DHSVM) with the stream temperature River Basin Model (RBM) to simulate spatiotemporal variability of stream temperature. Further, we improved the integrated model to account for the influence of snowmelt water on stream temperature and thermal habitats. We calibrated the model with observed snow, streamflow, and stream temperature distributed across the basin to ensure that our model can replicate spatiotemporal variability observed in the past. We then projected future stream temperature changes using 10 downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs) under the Representative Concentration Pathway (RCP) 8.5 climate change scenario. Suggestions for natural resource managers with the Tribes and other jurisdictions who need to identify climate-ready management strategies to protect/restore cold-water habitats is also provided.