Watershed Boundary Conditions for Global Change Impact Analysis

The U.S. Global Change Research Program (USGCRP) includes, among other issues, the impact of global change on water quality. This field study evaluates the impact of global changes (land-use change and climate change) on source water quality. Changes in source water quality can change the cost of drinking water treatment. Obvious changes to the upstream environment such as land development or natural resource production effect source water quality. Other changes that happen at a global scale, such as atmospheric warming or drought frequency alter the hydrologic cycle through atmospheric or groundwater processes which, in turn, may impact source water quality. Using data from two carefully selected watershed sites, this study weighs the relative merit of land-use practices as a means to mitigate impacts to source water from the large-scale atmospheric changes. This paper will present a unique framework for the site selection process. The goal of this process was to find sites for which we could define a "boundary" condition. "Boundary" in our context means more than the areal extent of the watershed; we need to define the boundary of the model state for some set of hydrologic parameters in time and space.