COS 254-3 - Simulating climate change impacts on basin scale water yield across the CONUS

Abstract: Forests are important sources of clean water supply in the U.S. However, climate change is projected to bring warmer temperatures and shifts in the precipitation regime, which can directly alter water yield in forested basins across the conterminous USA (CONUS). Additionally, changing climate can drive shifts in types and abundance of vegetation, which are important drivers of hydrologic processes within watersheds. Prior work using the well-validated Water Supply Stress Index (WaSSI) water balance model has documented the potential for climate change and forest thinning to interact to alter water yield. In this work, we integrate output from a dynamic global vegetation model (DGVM) with WaSSI to explore how shifts in vegetation driven by climate change can alter water yield across CONUS at the United States Geological Survey 8-digit Hydrologic Unit Code (HUC) scale. We ran MC2 DGVM to simulate changes in vegetation across CONUS under RCP4.5 and RCP8.5 climate change scenarios. We extracted future projections of vegetation shifts and LAI from the DGVM output and input into WaSSI to obtain future projections of water yield for each HUC8 watershed to year 2100. We document the spatial patterns of hydrological responses in different regions and the complex interplay between vegetation shift, ET and water yield. The results are integrated within a large ensemble of global climate models for quantifying uncertainty of future watershed US water supply and identifying likely vulnerable watersheds under a changing climate.