Predicting the Hydrologic Response of the Columbia River System to Climate Change
Wednesday, 17 December 2014: 5:15 PM
The Columbia River, located in the northwestern United States with headwaters in Canada (Pacific Northwest), is intensely managed for hydropower generation, irrigation, flood control, ecosystem services (particularly salmonids), navigation, and recreation. Effects of anthropogenic climate change already manifest themselves in the Pacific Northwest through reduced winter snow accumulation at lower elevations and earlier spring melt. As the climate warms, the Columbia River, whose flow regime is heavily dependent on seasonal snow melt, is likely to experience significant changes in the timing of its seasonal hydrograph and possibly in total flow volume. We report on a new study co-funded by the Bonneville Power Administration to update and enhance an existing climate change streamflow data set developed by the University of Washington Climate Impacts Group in 2009-2010. Our new study is based on the RCP4.5 and RCP8.5 climate projections from the Coupled Model Intercomparison Project Version 5 (CMIP5). In contrast to earlier studies, we are using a suite of three hydrologic models, the Variable Infiltration Capacity (VIC) model, the Unified Land Model and the Precipitation Runoff Modeling System, each implemented at 1/16 degree (~6 km) over the Pacific Northwest. In addition, we will use multiple statistical downscaling methods based on the output from a subset of 10 CMIP5 global climate models (GCMs). The use of multiple hydrologic models, downscaling methods and GCMs is motivated by the need to assess the impact of methodological choices in the modeling process on projected changes in Columbia River flows. We discuss the implementation of the three hydrologic models as well as our development of a glacier model for VIC, which is intended to better represent the effects of climate change on streamflows from the Columbia River headwaters region. Finally, we report on our application of a new auto-calibration method that uses an inverse routing scheme to develop spatially-distributed runoff fields from naturalized flows at gauge locations. This allows us to calibrate the hydrologic models at the level of the individual grid cell rather than sub-basin.