Evaluating the impacts of land use changes on hydrologic responses in the agricultural regions of Michigan and Wisconsin

Abstract. Hydrologic fluxes in the Great Lakes region have been altered relative to pre-settlement conditions in response to major land use changes during the past 150 yr. Land surface characteristics and processes including leaf area index, roughness, albedo, soil moisture, and rates of momentum, energy and water vapor exchange are strongly influenced by land use. Changes in land use including urbanization and de(/re)forestation continue to affect the nature and magnitude of groundwater – surface water interactions and water availability influencing ecosystems and their services. One of the goals of the present work is to develop a baseline scenario relative to which the impacts of land use changes on hydrological and environmental processes can be evaluated. In addition, the study can help in quantifying the potential impacts of future projected changes in land use in order to mitigate the negative impacts of these changes on goods and services of value to society. The present study explores the relationship between land use changes and hydrologic indicators within the agricultural regions of Michigan and Wisconsin. Two sets of land use data, the circa 1800 County Base and the 2001 National Land Cover Dataset, were used to setup the Soil and Water Assessment Tool (SWAT) model. First, sensitivity analyses were performed both based on pre-settlement and current land use scenarios and the most sensitive parameters were identified. Then, the model was calibrated against measured daily stream flow data obtained from eight United States Geological Survey gauging stations. The impacts of land use changes were studied at three scales: subbasin-level, watershed-level, and basin-level. At the subbasin level, most of the hydrologic behavior can be described by percent change in land cover. At the watershed scale, significant differences were observed based on the long-term average hydrologic fluxes under the current and pre-settlement scenarios. In addition, an overall increase in the amount of evapotranspiration and overland flow and overall decrease in the amount of baseflow and water yield were observed. However, at the basin-level, the majority of the area experienced increased overland flow, decreased baseflow, lateral flow, and recharge to aquifers, and minor changes in evapotranspiration and water yield.