Increase of tropical cyclone-induced coastal flooding due to historical sea level rise

Surges from tropical cyclones (TCs) cause significant damage in coastal areas. However, the contribution of historical sea level rise (SLR) to surge heights and thus the flooded areas has not been quantified on a global scale. Here, we use an open-source shallow water equation solver to estimate the impact of historical SLR on coastal flooding induced by all historical TCs with landfall from 1950 to 2025, according to the International Best Tracks Archive. We isolate the SLR effect through the comparison of factual simulations accounting for observed changes in sea level to counterfactual simulations without long term trends in sea levels. Results show that SLR has steadily increased the coastal area affected by TC-induced surges, from about 5% in 1950–1954 assuming mean tide levels (7% and 5% for minimum and maximum tide levels, respectively) to about 18% in 2021–2025 (22% and 13% for minimum and maximum tide levels, respectively) in comparison to the areas affected without SLR. The increase differs along coastlines, with maxima in relative increases of surge flooding along the North American Atlantic coastline and the Southeast Asian coastline. To put the numbers into perspective, we also estimate the associated increases assuming 1 m of local SLR and no changes in TC tracks and wind fields, reaching 146% under mean tide assumptions (192% for minimum tide levels and 92% for maximum tide levels). Results show that this is higher than expected assuming a linear relationship between SLR and relative increases in flood extents. Our analysis demonstrates the significant increase in flood extent induced by SLR already today. The generated data sets of factual and counterfactual coastal flooding extend ISIMIP3a climate-related forcing data, allowing for the evaluation and attribution of additional coastal impacts.