Spatiotemporal evolution of sediment supply in the Yangtze River Basin from 2006 to 2024: A hydrologically constrained diagnostic framework

Study Region: The Yangtze River Basin (YRB) exhibits heterogeneous hydrology and sediment transport, but basin-wide suspended sediment concentration (SSC) changes and responses to contrasting flow conditions remain unclear. Study Focus: We analysed 63,996 Landsat 5/7/8 images and SSC–discharge observations from 30 stations across eight sub-basins (2006–2024), integrating optical water type (OWT)-specific machine learning, long-term trend analysis, and station-specific SSC–discharge relationships. Two representative OWTs were retained, with optimal models achieving R² values of 0.56 and 0.73 and RMSE values of 62 and 44 g m⁻³ , respectively. New Hydrological Insights for the Region: SSC declined significantly across all seasons, most rapidly in autumn (−1.09 g m⁻³ yr⁻¹), with sensitivity tests confirming robust basin-wide declines under varying temporal data availability. Hydrologically normalised SSC anomalies showed that Normal Transport remained dominant under diagnostic thresholds of ±0.2, ±0.3, and ±0.4. Constrained responses strengthened particularly in the Main Stem, Jinsha River, and Poyang Lake. During floods, six sub-basins exhibited negative median sediment-response anomalies, whereas seven showed positive anomalies during droughts. This spatially heterogeneous flood–drought asymmetry reveals shifts in runoff–sediment coupling relative to local hydrological baselines rather than sediment responses simply proportional to runoff magnitude.