WEHY-HCM for Modeling Interactive Atmospheric-Hydrologic Processes at Watershed Scale. I: Model Description

Abstract

Among the key problems in atmospheric and hydrologic sciences are the modeling of the interaction between the atmosphere and land surface hydrology while also quantifying the surface/subsurface hydrologic flow processes both in vertical and lateral directions, and modeling the heterogeneity in surface and subsurface hydrologic processes. Meanwhile, in standard water resources engineering practice, the planning and management of the water resources is performed over the geographical region of a watershed. To address these issues, a model of coupled atmospheric-hydrologic processes at the watershed scale, the Watershed Environmental Hydrology Hydro-Climate Model (WEHY-HCM), has been developed. The atmospheric model PSU/NCAR MM5 (Fifth Generation Mesoscale Model) was coupled to the watershed hydrology model WEHY through the atmospheric boundary layer to form the WEHY-HCM. The WEHY-HCM is especially useful for producing nonexistent atmospheric data as input to the modeling of surface and subsurface hydrologic processes at sparsely gauged or ungauged watersheds. The continuously changing state of the atmospheric boundary layer may be essential information in the computation of evapotranspiration (ET) rates and other land surface fluxes. Because such land surface fluxes are the result of the interaction of land surface hydrologic processes with atmospheric processes, their realistic estimation necessitates the coupled modeling of these processes, as is done in the WEHY-HCM. The model is also useful at watersheds that have heterogeneous topography and land use/cover because the main model components are based on areally averaged, scalable conservation equations and parameters in order to quantify and account for the effect of heterogeneity within watersheds. In this paper, the modeling of an integrated system of atmospheric processes aloft coupled with atmospheric boundary layer processes, land surface processes, and surface and subsurface hydrologic processes is described at the scale of a watershed within the framework of WEHY-HCM.