A DISTRIBUTED HYDROLOGY-VEGETATION MODEL FOR COMPLEX TERRAIN

A distributed hydrology-vegetation model is described that includes ca nopy interception, evaporation, transpiration, and snow accumulation a nd melt, as well as runoff generation via the saturation excess mechan isms. Digital elevation data are used to model topographic controls on incoming solar radiation, air temperature, precipitation, and downslo pe water movement. Canopy evapotranspiration is represented via a two- layer Penman-Monteith formulation that incorporates local net solar ra diation, surface meteorology, soil characteristics and moisture status , and species-dependent leaf area index and stomatal resistance. Snow accumulation and ablation are modeled using an energy balance approach that includes the effects of local topography and vegetation cover. S aturated subsurface flow is modeled using a quasi three-dimensional ro uting scheme. The model was applied at a 180-m scale to the Middle For k Flathead River basin in northwestern Montana. This 2900-km2, snowmel t-dominated watershed ranges in elevation from 900 to over 3000 m. The model was calibrated using 2 years of recorded precipitation and stre amflow. The model was verified against 2 additional years of runoff an d against advanced very high resolution radiometer based spatial snow cover data at the 1-kM2 scale. Simulated discharge showed acceptable a greement with observations. The simulated areal patterns of snow cover were in general agreement with the remote sensing observations, but w ere lagged slightly in time.