APPLICATION OF A SUBGRID OROGRAPHIC PRECIPITATION SURFACE HYDROLOGY SCHEME TO A MOUNTAIN WATERSHED

A regional climate model including a physically based parameterization of the subgrid effects of topography on clouds and precipitation is d riven by observed meteorology on its lateral boundaries for a period o f 12 months. The meteorology simulated by the model for each subgrid e levation class is distributed across a mountain watershed according to the surface elevation within the watershed. The simulated meteorology is used to drive a detailed model of hydrology-vegetation dynamics at the topographic scale described by digital elevation data, 180 m. The watershed model, which includes a two-layer canopy model for evapotra nspiration, an energy-balance model for snow accumulation and melt, a two-layer rooting zone model, and a quasi-three-dimensional saturated subsurface flow model, is used to simulate the seasonal cycle of the a ccumulation and melt of snow and the accumulation and discharge of sur face water within a mountain watershed in northwestern Montana. Compar isons between. the simulated and the recorded snow cover and river dis charge at the base of the watershed indicate comparable if not better agreement than between the recorded fields and those simulated by the watershed model driven by meteorology observed at two stations within the watershed. The agreement with the recorded discharge, precipitatio n, and snow water equivalent is also clearly superior to simulations d riven by the regional climate model run without the subgrid parameteri zation but with one-third the grid size of the simulation with the sub grid parameterization.