Using backcast land-use change and groundwater travel-time models to generate land-use legacy maps for watershed management

We couple two spatial-temporal models, a backcast land-use change model and a groundwater flow model, to develop what we call "land-use legacy maps." We quantify how a land-use legacy map, created from maps of past land use and groundwater travel times, differs from a current land-use map. We show how these map differences can affect land-use planning and watershed management decisions at a variety of spatial and temporal scales. Our approach demonstrates that land-use legacy maps provide a more accurate representation of the linkage between land use/cover and current water quality compared to the current land-use map. We believe that the historical signatures of land-use impacts on current water quality should be considered in land-use planning and watershed management.