We ran RHESSys, a GIS-based, hydro-ecological modeling framework designed to simulate carbon, water and nutrient fluxes with observed and Global Climate Model (GCM) scenarios for an alpine and subalpine watershed in Rocky Mountain National Park, CO. RHESSys combines both a set of physically based process models and a methodology for partitioning and parameterizing the landscape. Loch Vale Watershed (LVWS) is a headwater catchment for the South Platte River Basin that serves as a source of water for Colorado Front Range populations and Great Plains agriculture. Streamflow in Loch Vale is driven primarily by snowmelt. Data from 18+ years of continuous monitoring of meterology, hydrology, water quality, and biogeochemistry is used for model testing and parameterization. RHESSys simulations predict changes in the timing of the spring melt with warmer climate scenarios. Model simulations indicate changes in basin-wide snowpack and total stream discharge from changes in precipitation and the seasonal timing of the precipitation. The CCC GCM predicts a warming trend over the next century without a substantial change in precipitation for the region near Rocky Mountain National Park. RHESSys simulations for this type of warming scenario predict LVWS streamflows would have more frequent low-flow years, raising the concern for possible drought. Nutrient fluxes in LVWS are closely tied to hydrology. RHESSys is used to simulate climate-driven changes in ecosystem (productivity and respiration) and nutrient fluxes.