Anthropogenic Regulation Decouples Sediment Fluxes From Environmental Drivers in the Upper Lhasa River Basin of the Tibetan Plateau

Riverine sediment, a critical element for biogeochemical cycles, is subject to the interacting controls of climate, vegetation, cryosphere processes and anthropogenic infrastructure. This study established a comprehensive attribution framework to quantify various drivers' contributions to suspended sediment flux (SSF) changes in the Upper Lhasa River Basin and analyse synchronous and asynchronous occurrence probabilities, thereby elucidating the profound impact of anthropogenic regulation on sediment transport mechanisms. Results indicate that reservoir commissioning coincided with a critical regime shift, transitioning sediment transport from a climate‐dominated to a regulation‐dominated state. Compared with the pre‐dam period (1982–2005), mean annual SSF in the post‐dam period (2006–2022) decreased by 78.8%, decoupling from the 14.8% reduction in discharge. Double mass curve analysis indicated that anthropogenic influences and precipitation variability accounted for 90.1% and 9.9% of the SSF reduction, respectively. Reservoir regulation disrupted longitudinal sediment connectivity and promoted an increasingly supply‐limited regime downstream. This transition overrode the effects of increased precipitation, discharge, and thaw depth, reversing the climate‐driven increase in SSF (42.5% 10 year −1 ) into a significant decline (−21.3% 10 year −1 ). Concurrently, anthropogenic regulation, particularly reservoir operation, weakened the responsiveness of SSF to environmental variability by attenuating the transmission of precipitation signals to sediment transport. Accordingly, precipitation–SSF synchrony declined from 63.4% to 41.9%, while the joint probability of high precipitation–high SSF decreased from 26.83% to 5.52%, providing indirect evidence consistent with sediment‐peak attenuation under reservoir regulation. These findings highlight the reshaping impact of reservoir regulation on sediment driving mechanisms and transport modes in alpine basins and provide a novel perspective for watershed management.