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Recent concern over environmental and economic impacts of urban sprawl has focused renewed attention on the importance of making full use of existing urban areas. Revitalizing former industrial, commercial, and residential areas often involves changes in land use type or intensity of use. It is important to have the ability to evaluate the long-term hydrological impacts of such changes. These impacts can then be placed within the context of impacts that similar land uses would have if a decision were made to place them in the urban fringe (urban sprawl) rather than in existing urban areas (urban renewal).

In this study, we illustrate how the Long-Term Hydrological Impact Analysis (L-THIA) tool can be used to compare the hydrological impacts of land use change in existing urban areas versus change in the urban fringe. L-THIA is a simple, comparative tool that requires the user to provide information on land use and soil type for existing and future/planned conditions. The tool combines this information with local rainfall data to calculate long-term average annual surface runoff under existing and future/planned conditions. L-THIA analyses can be run directly at our web site for locations throughout the US where the curve number technique is already routinely used (http://danpatch. ecn. purdue. edu/~ sprawl/L-THIA). By performing analyses of renewal versus conversion of agricultural land at the urban fringe, it is possible to provide a comparative assessment of impacts. This initial comparison can be helpful in educating the general public and decisionmakers, thereby raising awareness of this element of the set of variables that are considered in …