A coupled modeling system has been developed using the NCAR/PSU Mesoscale Model (MM5) and a modified form of the Biosphere Atmosphere Transfer Scheme (BATS) as the boundary layer parameterization. The modification allows for the effects of puddling. Surface puddling is allowed to occur when rainfall exceeds infiltration into the top soil layer. Puddled water, whose size is a function of vegetation cover, is then allowed to evaporate from a free water surface. The coupled model is also linked to a hydrologic model that produces hydrographs for the Huron River watershed in southeast Michigan. The hydrologic model, which divides a large watershed into numerous small watersheds, is easily transported to different watersheds to allow hydrologic modeling in other areas.
The coupled modeling system is being used to analyze the effects of surface puddling on energy fluxes, surface temperatures, precipitation, and streamflow for simulations in the Great Lakes region. The current version of the modeling system utilizes a coarse grid domain that encompasses the contiguous United States at 90 km grid resolution, a fine grid domain that encompasses the Great Lakes region at 30 km grid resolution, and a finer grid domain that encompasses the Huron River watershed at 10 km resolution. Results of multi-month simulations will be presented for the summer of 1995. Results from sensitivity simulations will also be presented to illustrate the impacts on the Huron River watershed of current, pre-settlement, and future land uses as well as selected climate change scenarios that will be provided through the US Global Change Research Program.