Progressive Coarsening of Tidal Flats Through Satellite Observations

Abstract Climate change‐induced wave energy enhancement and reduced sediment supply are driving surface sediment coarsening on tidal flats in the Yellow Sea coastal zone, which constitutes our hypothesis. However, large‐scale, long‐term empirical evidence supporting this hypothesis has been lacking. Here, we present the first comprehensive spatiotemporal analysis of tidal flat sediment coarsening across approximately 950 km of coastline from 2005 to 2024, based on a combination of numerical simulations, Landsat‐based remote sensing, and in situ data from 1,170 surface sediment samples. Using mean grain size as a quantitative metric, we document spatially heterogeneous but regionally widespread sediment coarsening trends across the study’s coastal transects. The analysis reveals significant correlations among the coarsening rate of surface sediments on tidal flats, the rate of change in surface suspended sediment concentration in marine waters, and the rate of topographic change on tidal flats. Our findings provide the first large‐scale, long‐term empirical validation of climate‐driven tidal flat coarsening and elucidate its underlying drivers. Given the pervasive intensification of wave energy and widespread reduction in riverine sediment supply across coastal systems, such tidal flat surface sediment coarsening likely represents a previously underrecognized regional coastal phenomenon with broader potential implications for global tidal flat systems.