A new SUMMA and MizuRoute hydrologic modeling resource for US water applications

Abstract:

Water-related applications and decision making from the short-range to the climate scale commonly rely on hydrologic modeling that must provide both strategic information over large domains as well as high quality information at local watershed scales. We present a major new capability for process-oriented hydrologic modeling, analysis and prediction that has been developed over the last five years in a collaboration between NCAR, federal water agencies, and several academic institutions. This implementation of the SUMMA hydrologic modeling framework and MizuRoute channel routing model now comprises a 50-year, 3-hour timestep retrospective simulation with a real-time extension suitable for drought monitoring, climate sensitivity studies, and streamflow prediction applications. SUMMA is applied at the watershed scale (USGS HUC12, extended into Canada and Mexico) with reach routing on the MERIT-Hydro channel network, with an initial focus on the western US. The efficient, intermediate-complexity simulations are driven by an ensemble of meteorological forcings, yielding rare insights on simulation uncertainty and providing avenues for ensemble data assimilation. Targeted parameter optimization workflows have yielded high-quality results in a wide range of watersheds as well as at the basin scale. The simulations support both short-range to seasonal ensemble forecasting (with potential to yield actionable information for reservoir system operations and management), as well as long-term hydrologic projections that can inform water security analyses, planning and policy. We describe the components of this modeling resource, including the latest status of the models, the forcing and parameter estimation methods, and also highlight key outcomes from state and federal water agency projects that leverage the modeling resource. We also share insights gained from research toward the next generation of this modeling capability, which is progressing in a measured fashion toward pragmatic sub-watershed discretization to increasingly resolve spatial variability in hydrologic phenomena, including extremes.