Urbanization is a growing trend world wide and presents many significant challenges in watershed planning. Distributed operational hydrology models can assist decision-makers in understanding the effects of land use and urban development policies on large watersheds, including runoff quantity and quality. The National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory (GLERL) has developed the Distributed Large Basin Runoff Model (DLBRM) as a large-scale model for the Great Lakes basin. This paper illustrates how the daily DLBRM may be used to model runoff impacts of urbanization. Urbanization trends within the Clinton watershed of Southeastern Michigan are discussed, including analysis of stationary stream flow trends of the watershed. Calibration issues regard-ing temporal parameter variability are also addressed followed by urbanization sce-nario simulations within the Clinton watershed. Urbanization and Hydrologic Impact Global urban population growth continues to outpace total population growth and,