Transforming stormwater management from Sponge City to Self-Purifying City

Urbanisation and climate change exacerbate water pollution, with runoff from impervious surfaces contaminating water bodies during rainfall. China's Sponge City initiative strategically conserves and/or restores nature to address urban runoff issues. However, Sponge City approaches are limited by single-media pollution control and insufficient pollutant removal capacity. The Self-Purifying City concept advances the Sponge City by integrating air, soil, and water systems to artificially purify cross-media pollutants and enhance overall environmental purification capacity. The transformation from Sponge Cities to Self-Purifying Cities remains underexplored in terms of strategies and laws. In this study, a total of 36 strategies and 141 environmental laws related to stormwater purification were extracted from 693 publications in the Web of Science database and 1539 documents from the Ecolex environmental law database, respectively. Through multidimensional analyses and evidence synthesis, this study explored the characteristics and synergies of these strategies and laws, proposing a transformative stormwater management framework that incorporates community-based, appropriate, and strategic approaches across business activities, financial support, individual behaviours, and institutional controls. Five key measures include mainstreaming Nature-based Solutions, mandating long-term monitoring, establishing dedicated funding mechanisms with incentives and penalties, strengthening stakeholder coordination through legislation, and using data-driven approaches for managing high-risk areas, which are recommended to ensure compliance and governance. To enhance the practical applicability of the proposed framework, we also demonstrate how it can be applied to nitrogen pollution control, thereby better protecting the environment and supporting the development of Self-Purifying Cities.