Assessing Biases and Errors in Non-Precipitation Forcing Fields for the National Water Model Configuration of WRF-Hydro

The streamflow predictions within the National Water Model configuration of WRF-Hydro are a product of the forcing fields input into the model. This study focuses on those non-precipitation inputs based on the HRRR (0-18 hours) and GFS (0-10 days) models, including temperature, wind, humidity, and radiation fluxes. We evaluated these fields at ~4,500 stations from several observation networks distributed across the contiguous U.S. Wind speed has a slight high bias (averaging 1.0 m s-1 for all stations) from both the HRRR and GFS model inputs, while temperature has a slight low (-0.4°C) bias from the GFS. These two biases would counteract each other in WRF Hydro in terms of evaporation of surface water, and melting and/or sublimation of snow cover. Shortwave radiation has a positive bias from both model forcing sources, maximizing around 40 W m-2 near solar noon, which is partially offset by a negative (-8 W m-2) net long wave bias spread out over all hours of the day. The net positive radiation bias would also result in more evaporation of surface water, and greater melting and/or sublimation of snow cover than reality. These model forcing biases have regional differences that will be discussed. This presentation also focuses on the effects of corresponding bias corrections applied to the WRF-Hydro Model, to account for these forcing mechanism biases.