Integrated assessment of climate change and urbanization impact on adaptation strategies: a case study in two small Korean watersheds

This study develops an integrated approach to assess climate change and urbanization impacts on adaptation strategies in watersheds. We considered the two adaptation strategies for two small watersheds in Korea: the redevelopment of an existing reservoir and the reuse of highly treated wastewater treatment plant (WWTP) effluent. Climate change scenarios were obtained by statistically downscaling the predicted precipitation and temperature with a global climate model (A1B and A2), and urbanization scenarios were derived by estimating the impervious area ratios with an impervious cover model. With the climate change and urbanization scenarios, we used the Hydrological Simulation Program-Fortran model to derive the flow and biochemical oxygen demand (BOD) concentration (conc.) duration curves, and calculate the numbers of days satisfying environmental requirement for instreamflow and the target BOD conc. Climate change reduced the effectiveness of the adaptation strategies with respect to low flow and BOD conc., whereas urbanization generally increased their effectiveness. Climate change had a greater impact on the effectiveness of the adaptation strategies for BOD conc. than for low flow, whereas urbanization had a greater impact on low flow. Comparing impacts of two strategies, a larger decrease in the effectiveness was observed for the WWTP effluent reuse strategy in response to climate change and urbanization. However, the consistent trends cannot be found with ease if climate change and urbanization happens jointly.