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

Accelerating global sea-level rise (SLR) is fundamentally restructuring coastal flood regimes, particularly in complex estuarine systems where fluvial-tidal interactions govern hydrological extremes. In this study, we reveal a significant increasing trend in compound flooding probability across 20 strategically selected basins spanning tropical mega-deltas to high-latitude systems, where extreme fluvial flooding coincides with high-tide flooding. CMIP6-driven ensemble modeling reveals disparate growth rates between flood drivers, specifically a 273.6% ( p < 0.01) increase in high-tide flooding frequency contrasted with a 10.6% fluvial flooding frequency increase, highlighting their markedly divergent responses to climatic forcing. With high-resolution fluvial flooding and high-tide flooding coupling hydrodynamic simulation, SLR-driven compound flooding will affect upstream regions farther from the estuary due to the backwater effect, amplifying inundation extent by 23–54% compared to single-flood scenarios under 99th percentile compound extremes. Our findings emphasize that SLR fundamentally reshapes fluvial flood dynamics through estuarine-tributary coupling, a key mechanism for interpreting shifting flood impacts under a changing climate.