Timothy M. Lahmers1, Christopher L. Castro1, Hoshin V. Gupta1, David J. Gochis2, Aubrey Dugger2, Mike Smith3
1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona
2Research Application Laboratory, National Center for Atmospheric Research, Boulder, Colorado
3Office of Water Prediction Analysis and Predictions Division, NOAA/NWS, Silver Spring, Maryland
The NOAA National Water Model (NWM), which is based on the WRF-Hydro architecture, became operational in the summer of 2016 to produce streamflow forecasts nationwide. In order to improve the physical process representation of NWM/WRF-Hydro, a parameterized channel infiltration function is added to the Muskingum-Cunge channel routing scheme. Representation of transmission losses along streams was previously not supported by WRF-Hydro, even though most channels in the southwest CONUS have a high depth to groundwater, and are consequently a source for recharge throughout the region. The LSM, routing grid, baseflow bucket model, and channel parameters of the modified version of NWM/WRF-Hydro are calibrated using spatial regularization in selected basins in the Southwest CONUS. WRF-Hydro is calibrated and tested in the Verde and San Pedro basins. The model is forced with NCEP Stage-IV and NLDAS-2 precipitation for calibration, and the effects of ephemeral channel infiltration on model performance are considered. This work advances the regional performance of WRF-Hydro through process enhancement and calibration that is highly relevant for improving model fidelity in semi-arid climates.