Cascade Reservoirs Reshape Environmental Constraints on Vegetation Phenology in Alpine Riparian Ecosystems

Abstract

With nearly two‐thirds of global long rivers regulated by dams, the development of cascade reservoirs profoundly alters riparian ecohydrology, yet isolating their net ecological effects from global warming remains a critical challenge. Integrating the difference in differences (DID) method, structural equation modeling (SEM), and an interpretable machine learning framework with multi‐source remote sensing data (2001–2020), this study decouples the impacts of cascade reservoirs on riparian vegetation phenology within the transboundary Lancang‐Mekong River. While climate warming generally advances the start of the growing season (SOS) and delays the end of the growing season (EOS) across the Lancang River Basin, cascade reservoirs reshape this trajectory within a 5 km buffer along the dammed reaches. After isolating the climatic background, reservoir regulation counteracts the advancing SOS with a relative delay of 6.3 days, while further delaying EOS by 2.5 days (driven primarily by the 2–5 km band). This seasonally asymmetric intervention stems from localized hydrothermal alterations. In spring, the reservoir‐induced asymmetric warming reduces chilling accumulation, elevating the forcing temperature threshold and tending to desensitize vegetation to warming. Conversely, in autumn, while reservoirs alleviate moisture deficits, their thermal inertia introduces elevated nighttime thermal stress, shifting the dominant EOS limiting factor from moisture availability to temperature constraints. By uncovering these microclimatic mechanisms, this study provides a vital scientific basis for sustainable hydropower and adaptive ecosystem management in regulated alpine river systems.