A conceptual framework for implementing green-grey infrastructures to mitigate urban flood through source-to-hazard intervention pattern

The urgency of tackling flood disaster in coastal cities has grown due to the impact of climate change and rapid urbanization. Implementing a combination of green and grey infrastructures has emerged as a highly effective approach for mitigating urban flooding. Given the complex dynamics of urban runoff, it is crucial to evaluate various strategies involving these infrastructures to efficiently manage flood risk. To address these challenges, this study proposes a conceptual framework aimed at implementing green-grey infrastructure strategies, with a specific focus on mitigating flood volume from source area to hazard area. By employing a tracer-aided urban flood model, this framework can effectively decrease flood volume within drainage systems, thereby reducing potential losses from urban flooding. Furthermore, the cost-benefit of green-grey infrastructure in flood management was thoroughly assessed, providing a robust quantitative foundation for flood mitigation and cost management. The framework was successfully applied to the Longkungou drainage system in Haikou City. The results showed a reduction in flood volume by 339836 m3, with a reduction rate of 36.1%, which achieved the expected flood mitigation target. Cost-benefit analysis further revealed that relying solely on either grey or green infrastructure is inadequate for optimal stormwater management. While grey infrastructure demonstrates high efficiency in addressing major flood events, green infrastructure offers significant environmental benefits and is particularly effective for smaller rainfall events. The integration of both green and grey infrastructures has been proved to be the most beneficial overall for disaster mitigation. In summary, this study highlights the importance of combining green and grey infrastructure strategies to achieve comprehensive and effective urban flood management.