Climate Change Impacts Across the Columbia River Basin: What Do 172 Projections Tell Us about Model Uncertainty?

River flows and water storage in the Columbia River Basin (CRB) are intensively managed to optimize hydropower, flood control, irrigation, ecosystem function and recreation. Water management systems in the basin have been designed to accommodate a hydrologic regime dominated by winter snow accumulation and a subsequent snowmelt peak in the spring. Anthropogenic climate change has already begun to cause changes to this hydrologic regime, but the extent of future changes remains uncertain. The uncertainty stems in part from a lack of understanding of the effect of that methodological choices have on future projections.  An improved understanding of that uncertainty will assist regional stakeholders in adapting their management plans. Toward the goal of better understanding the uncertainty in projected changes, we created a dataset encompassing of outputs from ten different global climate models (GCMs) and two different representative concentration pathways (RCPs) downscaled using three distinct methods. We used those outputs to force two different calibrated hydrologic models and used three independently-derived parameter sets for one of the models. Both models were implemented at 1/16^th degree scale (~5 km) across the Pacific Northwest (PNW). The various permutations resulted in a dataset from 1950-2099 comprised of 172 unique simulations. We will share results from this large dataset, first by showing climate impacts on key hydrologic variables such as snow water equivalent, soil moisture and evapotranspiration across the region. We will then investigate the resulting impacts on streamflow at key locations throughout the PNW. We will also address how large-scale simulations can better quantify model uncertainty under a changing climate.