Precipitation variability and the future of water in the West: A multi-catchment analysis

Abstract:

To evaluate the robustness of future projections of surface water, i.e. runoff, across the western United States, it is necessary to first generate an observed baseline of historical hydrology. A particular gap in current understanding is the relationship between precipitation variability, surface runoff generation, and the water-energy balance. In this study we construct a historical hydrological analysis using observations from 232 undisturbed HUC08 catchments and 25 large basins across the western US. We use this framework to evaluate the realism of CMIP6 portrayals of historical climate with a focus on key signatures, such as runoff efficiency, aridity, and precipitation variability. Both the models and observations are analyzed within a Budyko framework that quantifies the climatological relationships among these indicators. The interaction between precipitation variability and runoff efficiency is then further assessed on both intra- and inter-annual time scales. We demonstrate significant regional differences in the relationship between warm season precipitation variability and runoff efficiency, which has important implications for understanding of how climate variability and change will contribute to future surface water availability.