Ecosystem Service-based Flood Risk Assessment for the Pearl River Basin

Abstract Regulating flood risk based on ecosystem services like water conservation has been widely adopted, but quantitative methods often fail to decouple the effects of precipitation from land cover. This study proposes a new perspective on assessing flood risk by analyzing the partitioning of precipitation into water conservation and surface runoff, using multi-source data from the Pearl River Basin (2020–2022). In this study, the InVEST model simulated hydrological components, with outputs closely matching observed runoff data. Ratios of precipitation converted into water conservation and quick flow are proposed as novel indicators to assess a basin’s flood mitigation capacity and risk level, respectively. Results show that while precipitation is the primary driver, land use is the key modulator. Sub-basins with high forest cover (e.g., Beijiang, > 60%) exhibit high water conservation conversion ratios (> 0.30), indicating strong flood mitigation potential. Conversely, the highly urbanized Pearl River Delta (21.67% built-up area) shows the highest quick flow conversion ratio (0.24), resulting in a significantly higher flood risk under equivalent rainfall conditions. This study substantiates the practical application of using precipitation partitioning as a tool for flood risk assessment, highlighting the critical need for integrating land use planning and green infrastructure development into regional flood mitigation strategies.