Title: Advancing process based hydrologic models for risk assessments
Presenting Author: Martyn Clark
Organization: NCAR
Co-Author(s): Grey Nearing, Bart Nijssen, Sujay Kumar, Christa Peters-Lidard

Abstract:
Management decisions about our nation's water resources are made against a backdrop of uncertainty. One important source of uncertainty that has so far been neglected in operational settings stems from the hydrologic models that are used in making predictions. This presentation describes the advancement of a new hydrologic modeling tool, SUMMA (the Structure for Unifying Multiple Modeling Alternatives), which provides a systematic and controlled approach to building large ensembles of hydrologic model structures (up to millions of members). By using a common modeling core in SUMMA, the overhead associated with implementing alternative modeling approaches is significantly reduced, a major departure from current "small ensemble" methods. This presentation will describe efforts to embed SUMMA within NASA's Land Information System (LIS), and provide examples of "large ensemble" simulations over continental domains. The outcome from this work is the capability to design ensemble systems with specific properties (i.e., covering all major sources of hydrololgic modeling uncertainty), hence improving the statistical reliability of risk assessments used for water resources planning and management.