Global acceleration of compound flood risks through fluvial-tidal interactions in a warming climate

This study presents a global assessment of how sea‑level rise and changing hydrological extremes are accelerating the risk of compound flooding in major river–estuary systems worldwide. Drawing on observational data, CMIP6 climate projections and coupled hydrodynamic modelling, it examines why and how fluvial floods and high‑tide floods increasingly coincide, and identifies where these risks are most acute—particularly in tropical and subtropical deltas. The study is intended for researchers, planners and disaster risk reduction practitioners seeking to understand the evolving dynamics of compound flood hazards between 1950 and 2050. Key DRR insights include the finding that high‑tide flooding is increasing far more rapidly than fluvial flooding, that sea‑level rise is reshaping upstream flood behaviour through backwater effects, and that compound events are projected to intensify across all 20 basins studied. 

The study recommends strengthening integrated flood‑risk management by explicitly accounting for the interaction between riverine and tidal processes, as compound events can increase inundation extent by 23–54% compared with single‑driver floods. It highlights the need for basin‑specific adaptation strategies, improved monitoring of high‑tide flooding, and the incorporation of coupled fluvial–tidal dynamics into future planning. Lessons learned emphasise that relying on single‑hazard assessments will underestimate risk, that small and medium‑sized basins may face the fastest intensification of extremes, and that climate‑driven changes in both precipitation and sea‑level rise must be jointly considered to design effective mitigation and resilience measures.