A new watershed regulation capacity assessment approach based on scale theory and its applications

Study region The Qinhuai River Basin (Nanjing) Study focus Urbanization and extreme rainfall events are key factors affecting watershed regulation capacity. This study presents a basin regulation capacity assessment model based on scale theory. A power-law relationship between flow and catchment area is established to extract scale parameters, which serve as quantitative indicators of regulation capacity. Using the HEC-HMS and PLUS models, flow–area relationships under different scenarios are fitted to derive this indicator. The spatiotemporal distribution and trends of regulation capacity are then analyzed, considering various extreme rainfall and urban development scenarios. New hydrological insights for the region From 1990–2020, the basin's regulation capacity exhibited a declining trend with considerable interannual fluctuations. All regions of the basin exert a suppressive effect on flow increases, with the mid- and downstream areas relying on measures such as pumping and gate operations to maintain a relatively strong regulation capacity. Rainfall peaks were categorized as early (Type I), late (Type II), and central (Type III). Regulation capacity was weakest under Type I rainfall, whereas Types II and III exhibited the strongest regulation during a 50-year return period storm. Among four urban development scenarios, the ecological-priority scenario showed the best regulation capacity. Future basin planning should focus on ecological restoration, optimize natural retention areas, and enhance regulation measures under Type I rainfall.