Linking atmospheric and hydrologic models at the basin scale

This paper describes the development of a modeling system that provides a physically based robust model chain to link global, decade-scale climate inputs to vegetation change and river basin flow studies. The regional climate model, RegCM2 (Giorgi et al., 1993a and 1993b), is downscaled with the orographic microscale model, ZOOM, to create a model estimate at the point of interest in space. We have completed RegCM2 runs at 50 km resolution using ECMWF observational analysis input data over the Western U.S. for 16 years (1 Dec 1978 through 12 Dec 1994). We performed a "box analysis" (250 sq. km box) of 50 km RegCM2 runs, each having averaged model and observed data, comparing the two for temperatures and precipitation. ZOOM provides data at distributed points within the watershed to better represent the hydrologic processes in the watershed. The Climate Vegetation Hydrologic Model (CVHM) is a daily time-step hydrologic model based on the hydrologic response unit (Sikka, 1993), which requires inputs at points within each HRU, provided by ZOOM. This paper presents six years of the nested model runs for both the atmospheric (RegCM2, ZOOM) and the basin models (CVHM).