The Role of Parameterizations and Model Coupling on Simulations of Energy and Water Balances – Investigations With the Atmospheric Model WRF and the Hydrologic Model WRF‐Hydro

The distributed hydrologic model WRF-Hydro can operate in a fully-coupled mode with the atmospheric Weather, Research and Forecasting (WRF) model. WRF-Hydro enhances the modeling of terrestrial hydrologic processes in coupled WRF/WRF-Hydro by simulating lateral surface and subsurface water flows. The objectives of this study are (a) to examine the effect of WRF-Hydro on the surface energy and water balance in fully-coupled WRF/WRF-Hydro simulations and (b) to examine the impact of five WRF physics parameterizations on WRF-Hydro streamflow. The study area is the Mediterranean island of Cyprus and 31 mountainous watersheds. The domain-average soil moisture was 20% higher in the coupled WRF/WRF-Hydro, relative to the standalone WRF model, during a 1-year simulation. The higher soil moisture could explain the increase in latent heat (36%) and evapotranspiration (33%). The increase in these fluxes was less with a modification in the model transpiration parameterization to represent nocturnal transpiration and the use of remote sensing leaf area index data. The simulated precipitation of the coupled model increased up to 3%, relative to WRF. Two-year long WRF-Hydro simulations gave a median Nash-Sutcliffe Efficiency for daily streamflow of the 31 watersheds of 0.5 for observed precipitation forcing and between −1.9 and 0.2 for the forcing of the five WRF parameterizations. This study showed that the enhancement of the standalone WRF model with lateral water flow processes in the coupled mode with WRF-Hydro modifies the terrestrial energy and water balance. The improved terrestrial process representation should be considered for future hydrological cycle studies with WRF.