Evaluation of the NWS Distributed Hydrologic Model over the Trinity River Basin in Texas

Distributed hydrologic models are a promising tool for producing streamflow and other hydrologic information at high spatial resolution. In ongoing research at the University of Texas at Arlington, the Research Distributed Hydrologic Model (RDHM) developed by the National Weather Service (NWS) Hydrology Laboratory (HL) is being used to model sub-basins within the Trinity River Basin that extends from North Texas to the upper Texas Gulf Coast for a 16 year period from 1996 to 2011. The purpose is to evaluate simulation of streamflow, runoff and soil moisture at hourly time steps on a 4x4 km2 grid scale to explore possible hydrologic and water resources applications. RDHM uses the heat transfer version of the Sacramento soil moisture accounting model (SAC-HT) to simulate rainfall-runoff and the kinematic-wave hillslope and channel routing models for routing streamflow. For this project, the SAC-HT model was forced using hourly multi-sensor (radar, rain gauge, satellite) precipitation estimates produced by the NWS West Gulf River Forecast Center (WGRFC) that began in 1996. A priori parameters for the rainfall-runoff and routing models were derived from physical properties of soil and land-use data and stream channel cross-section data, respectively. Modeling results were evaluated using observed hourly streamflow data from 28 locations (10 unregulated, 18 regulated) within the basin and soil moisture data from one Soil Climate Analysis Network (SCAN) station. For unregulated locations, the quality of streamflow simulations was event-based and assessed in terms of amplitude and phase. However, streamflow simulations for the regulated locations were examined at larger temporal scales where the effects of regulation could be considered negligible. Finally, model-simulated water balance results over different spatiotemporal scales of aggregation were analyzed for potential utility to support various water resources applications.