Is the sponge city construction sufficiently adaptable for the future stormwater management under climate change?

Climate change increases the uncertainties associated with the future urban stormwater management. This study employed the Personal Computer Stormwater Management Model to evaluate the impact of climate change on problems associated with stormwater management at the city scale. These include urban flooding, non-point source (NPS) pollution, and combined sewer overflow (CSO) pollution. Multiple methods were adopted to overcome the difficulties when building credible modellings. Time partitioning and sectional difference were used during the calibration of hydrological and hydraulic parameters. The groundwater/river infiltration was assessed via extensive monitoring. The field rainfall simulator system was used to determine NPS parameters. Promising adaptions of sponge city construction in response to climate change were further evaluated. The adaption strategies were set in strict accordance with the "Sponge City Construction Systematization Program". The results showed that future climate change will increase the urban flooding risk, both NPS and CSO pollution loads, and will worsen river water quality. Sponge city construction was demonstrated to be a no-regrets adaption strategy toward the reduction of the combined pressures induced by changing climate. However, the adaptability was insufficient and varies largely with regard to concentration pathways, rainfall intensities, and pollutants. In best case scenarios, the flooding risk as well as diffuse pollution loads can be decreased to or below their current level under future climate change. However, the current level needs to be considered, since the urban drainage function was far from sufficient and the water quality was very poor. The increased NPS pollution risk was noticed after sponge city construction. Especially, for chemical oxygen demand and suspended solids, the increased NPS loads could even offset the decreased CSO pollution loads. Thus, flexibility is suggested to be allowed in the design of storm-drainage and pollution-control measures in future urban stormwater management.