A Novel Methodology to Identify Priority Areas for Stormwater Management Practices

Urbanisation and subsequent urban sprawl significantly increase impervious surfaces, intensifying stormwater runoff and flood risks. Sustainable stormwater management practices are effective strategies for mitigating runoff impacts. However, the strategic prioritisation of locations for implementing these practices at the catchment scale to maximise flood mitigation benefits remains underexplored. This study adopted the Soil and Water Assessment Tool (SWAT) to simulate hydrological processes across various land uses within the 2631 km² Qinhuai River basin, China. To identify hydrologically sensitive areas, this study utilised a surface runoff ratio analysis at the Hydrologic Response Unit (HRU) scale on monthly and annual time steps. This analysis identified 61 urban, 53 dry agricultural, 8 forest, and 26 paddy field HRUs as hydrologically sensitive. Catchment-wide scenarios for implementing Low Impact Development (LID) and Best Management Practice (BMP) were modelled and evaluated. Results demonstrated that all applied schemes met China’s Sponge City requirement of 80% annual rainfall capture ratio. These sustainable solutions effectively reduced runoff volumes and peak flows, with runoff reductions closely linked to treated area although peak attenuation showed less clear proportionality. Urban expansion increased runoff while decreasing paddies reduced contributions. Paddy fields remained the primary source of evapotranspiration (ET) in the basin. However, a notable increasing trend in ET was observed specifically from urban and agricultural lands, highlighting the significant influence of land use changes on regional hydrological processes.