Modelling the combined impact of sea level rise, land subsidence, and tropical cyclones in compound flooding of coastal cities

Low-lying coastal areas are threatened worldwide by compound flooding effects, including sea-level rise (SLR), frequent tropical cyclones (TCs), and accelerated land subsidence (LS). Compound flooding results in a negative effect, creating challenges for decision-making and coastal management for sustainable urban development. To comprehend the precise consequences and the combined effect of LS and SLR on coastal cities and to inform management scientifically, we initially chose historical TCs (TC6311 and TC1415) that resulted in exceptionally high surges and significant losses as reference scenarios for simulating potential compound events. We then utilized a hydrodynamic model, which combines TCs, LS, and SLR, to simulate the combined impact of flood hazards. Our findings indicated that the highest subsidence rate exceeds −20 mm/yr, the cumulative subsidence reaches −119.09 mm and 68.44% of the land is experiencing subsidence from 2015 to 2021. When comparing flood scenarios with and without the influence of SLR, the most severely affected by LS is projected to become submerged and completely inundated by 2100. We found that the combined impact of SLR and LS significantly amplified flood inundation and SLR is the primary amplification factor of flooding, projected to account for 46.2% by 2100. The framework established in this study facilitates the quantitative assessment of the interactions among multi-driver factors of compound flooding, thereby serving as a supplementary and guiding tool for future risk management.