Forecasting streamflow response to increased imperviousness in an urbanizing Midwestern watershed using a coupled modeling approach

• We present a modeling approach to estimate the hydrologic effects of urban growth.
• We generated percent imperviousness estimates for three urban growth scenarios.
• The effects of controlled versus uncontrolled growth were compared.
• Changes to runoff, evapotranspiration, and baseflow were observed.
• Comprehensive growth strategies are necessary to mitigate hydrologic impacts of urbanization.

Increased impervious surface (IS) cover is often the primary disturbance contributing to altered hydrology in urbanizing watersheds, affecting various components of the hydrologic balance. To improve the understanding of how future urban development will influence watershed streamflow characteristics, and to develop growth strategies that preserve water resources, it is necessary to combine detailed estimates of future IS cover with hydrologic models. A coupled modeling approach is presented to help address this problem. Pixel-based percentage IS cover for the period 2011–2031 was derived using the Imperviousness Change Analysis Tool (I-CAT) for three urban growth scenarios and coupled with the Soil Water Assessment Tool (SWAT) to simulate the potential hydrologic impacts of future urbanization in Hinkson Creek watershed, located in the Midwestern U.S. state of Missouri. Increases to average annual streamflow (+12.81% to +19.74%), increases to average annual surface runoff (+14.32% to +16.77%), reductions to evapotranspiration (−8.68% to −13.37%), and slight increases to baseflow were observed for the three growth scenarios. The approach used here created a range of possible future conditions for the study watershed and presented a framework that allows planners to couple realistic IS cover estimates with hydrologic models. Additionally, this study emphasized that a controlled, more environmentally conscious growth pattern does not necessarily produce less pronounced hydrologic impacts for the study watershed compared to an uncontrolled growth pattern, underscoring the importance of considering neighboring watersheds when analyzing the hydrologic impacts of urban development for an area.