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

Hydrologic fluxes in the Great Lakes region have changed relative to pre-settlement conditions in response to major land use changes during the past 150 years. 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 (LU1800) and the 2001 National Land Cover Dataset (NLCD 2001), were used to setup the Soil and Water Assessment Tool (SWAT) model. The model was calibrated against measured daily stream flow data obtained from eight United States Geological Survey (USGS) gauging stations. Sensitivity analysis were performed both based on pre-settlement and current land use scenarios. The following parameters are identified as most sensitive to land use change: initial SCS curve number for moisture condition II, depth from soil surface to bottom of layer, deep aquifer percolation fraction, and maximum canopy storage. The impacts of land use changes were studied at four scales: Hydrologic response unit (HRU), subbasin-level, watershed-level, and basin-level. At HRU-level, the results showed that the hydrologic behavior of land use change cannot be represented by a single metric, however, most of hydrologic behavior can be described by percent change in landcover at subbasin level. At the watershed scale, an overall increase in amount of ET and overland flow and overall decrease in amount of baseflow and water yield were observed. The majority of the basin area experienced increased overland flow, decreased baseflow, and minor changes in ET and water yield.