Eco-morphodynamic response of deltaic salt marshes to successive extreme storms

Deltaic salt marshes deliver crucial ecosystem services, including wave and flooding attenuation, making them key components of coastal nature-based solutions. However, their sustainability under climate change remains poorly understood, particularly regarding cumulative impacts from successive extreme weather events in regions with declining fluvial sediment supply. Here, we investigate the recovery capacity of deltaic salt marshes following successive extreme storms. We leverage in-situ data on intertidal hydrodynamics, bed elevation changes, and marsh vegetation dynamics, collected during typhoon and cold wave events in the East Chongming Wetland, the largest open tidal wetland in the Changjiang (Yangtze) Delta, China. Our results demonstrate that both typhoons and cold waves enhanced intertidal hydrodynamic forcing (inundation depth, wave energy, and tidal currents) and suspended sediment concentrations in vegetated areas, resulting in mean net bed erosion of 2.98 and 4.82 cm, respectively. The total salt marsh area decreased by 15.7% (from 7.05 × 10⁵ to 5.94 × 10⁵ m²) after the storms, with fragmentation increasing 50.8% between 2022 and 2023. Elevation-dependent responses generated two distinct bands of alongshore marsh erosion and vegetation loss. Cold waves caused particularly severe impacts through combined hydromechanical stress and belowground tissue damage from rapid temperature cooling. These findings reveal compounding stressors from sequential extreme hydrometeorological events that threaten the recovery of exposed salt marshes, providing critical insights for nature-based coastal protection and disaster adaptation strategies.