Multi-Scale Responses of Sediment Yield to Climate and Human Drivers in the Upper Yangtze River Basin

Global sediment reduction threatens deltaic sustainability and channel stability. While climatic and anthropogenic drivers are recognized, their cross-scale interactions remain poorly understood. This study investigated area-specific sediment yield (SSY) and its driving mechanisms across 14 stations (1.9 × 104 to 1.0 × 106 km2) in the Upper Yangtze River Basin (UYRB) from 1960 to 2018 using PLS-SEM and power-law scaling. Results show that by 2018, reservoir capacity reached 165.5 billion m3, regulating 38% of annual runoff. SSY significantly declined at 12 of 14 stations, with abrupt change points clustering around 1985. We found that intensive human interventions have fundamentally restructured the natural scale dependency of SSY, with the scaling exponent (β) shifting from a stable near-zero value to violent fluctuations (−0.2 to 0.5). Temporally, the dominant driver transitioned from hydro-climatic factors to dam-induced regulation. Spatially, the “filtering effect” of dams intensified with increasing drainage area, whereas smaller watersheds remained disproportionately sensitive to extreme precipitation. This scale-based divergence reveals a critical vulnerability: while mega-dams mitigate sediment at the basin scale, smaller catchments face elevated risks of high sediment delivery under intensifying climate extremes. These findings provide evidence of human-induced scaling instability in a large river system and highlight the necessity of scale-sensitive governance to ensure geomorphic and ecological resilience worldwide.