Tropical Cyclone Storm Surge-Based Flood Risk Assessment Under Combined Scenarios of High Tides and Sea-Level Rise: A Case Study of Hainan Island, China

In the context of climate change, coastal flood risk is intensifying globally, particularly in China, where intricate coastlines and frequent tropical cyclones make storm surges a major concern. Despite local government's efforts to initiate coastal monitoring networks and qualitative risk guidelines, there remains a gap in detailed and efficient quantitative assessments for combinations of multiple sea-level components. To address this, we develop the Tropical Cyclone Storm Surge-based Flood Risk Assessment under Combined Scenarios (TCSoS-FRACS). This framework integrates impacts of storm surges, high tides, and sea-level rise using a hybrid of statistical and dynamic models to balance reliability and efficiency. By combining hazard, exposure, and vulnerability, it incorporates economic and demographic factors for a deeper understanding of risk composition. Applying TCSoS-FRACS to Hainan Island reveals that the combined effects of storm surges, high tides, and sea-level rise significantly amplify local coastal flood risk, increasing economic losses to 4.27-5.90 times and affected populations to 4.96-6.23 times. Additionally, transitioning from Fossil-fueled Development (SSP5-8.5) to Sustainability (SSP1-1.9) can reduce the risk increase by approximately half. The equivalence in flood hazard between current high tides and future sea level under a sustainable scenario boosts confidence in climate change adaptation efforts. However, coastal cities with low hazard but high exposure need heightened vigilance in flood defense, as future risk could escalate sharply. Our study provides new insights into coastal flood risk on Hainan Island and other regions with similar profiles, offering a transferable and efficient tool for disaster risk management and aiding in regional sustainable development.