Implementation and evaluation of channel infiltration in the NOAA National Water Model for semi-arid environments

The NOAA National Water Model (NWM), operated by the NOAA National Weather Service (NWS) Office of Water Prediction (NWS/OWP), is an operational system, which provides hydrologic guidance throughout the Contiguous United States (CONUS). Based on the WRF-Hydro model architecture developed by the National Center for Atmospheric Research (NCAR), the NWM as it is currently configured does not explicitly resolve infiltration from ephemeral channels into the underlying unsaturated soil layers. Channel infiltration is an important source of groundwater recharge and can be a significant component of the water budget in semi-arid environments, including the southwest CONUS. As a result of this limitation, the NWM has difficulty simulating low water conditions in many basins in this and other semi-arid regions, despite multiple iterations of calibration.

For this study, we demonstrate 1) the capability of NWM v1.2 with a conceptual channel infiltration function to resolve streamflow in semi-arid environments after calibration in 49 basins, 2) evaluation of soil moisture compared to NOAA Hydrometeorology Testbed (HMT) sites in the Russian and Babocomari River basins from our modified NWM v1.2 configuration, and 3) channel infiltration in the latest version of the NWM (v2.1) compared to the model configuration now in development. For NWM v2.1, the calibration methods follow those of NCAR and NWS/OWP for the operational version of the model.

Results from NWM v1.2 show that the modified model structure is able to capture hydrologic response in semi-arid environments; however, it is limited by the uncertainty of forcing precipitation and other structural deficiencies of the NWM that cannot be resolved through calibration. This testing of the NWM calibration methods and evaluation of model states may be used to inform further development of WRF-Hydro for both operational and experimental purposes.