Climate change is expected to alter temperature and precipitation regimes across the globe and have varying effects on localized hydrological processes. For Silver Bow Creek (SBC), a headwater to the Clark Fork River in western Montana, the magnitude, duration, and frequency of spring runoff and summer base flow are dependent on the processes of snow accumulation and melt. Headwater hydrology and mountain streams will likely experience earlier snowmelt, increased spring flows, and decreased summer flows due to climate change.

A process-based hydrological model the Soil and Water Assessment Tool (SWAT) was used to evaluate the effects of climate change on SBC spring runoff and summer base flows. SWAT is a continuous simulation model that allows the user to predict surface water discharge, sediment loading, and stream nutrient content from user specified meteorological forcing functions. The SBC model was developed using 1/3 arc second DEM, SSURGO soil database, Montana land cover framework, and observed climatic data and was calibrated between the years 2008-2009 and validated between the years 2010-2011 to daily USGS flow data. Projected future downscaled climate change from CMIP5 emission scenarios RCP 2.6, 4.5, 6.0, and 8.5 were used as temperature and precipitation for the modeling period. A calibrated and validated baseline model was used for comparison against the four CMIP5 scenarios. Results were then used to make qualitative inferences about changes in surface water quality due to climate change. Model simulations indicate the timing of spring melt off to be earlier, the duration shorter, and volume to be less than the baseline scenario. One of the limitations to this study was the inability to satisfactorily calibrate and validate daily values.