A Subtle Atmospheric Shift Is Redefining Winter Hydrology on the Tibetan Plateau

Abstract

Abstract Winter climate over the Tibetan Plateau has long been characterized by cold conditions that preserve snow and regulate downstream water supply through delayed melt. Here we show that this buffering function is weakening in the Sanjiangyuan region due to a shift in winter compound climate regimes. Using standardized temperature–precipitation anomaly classification, circulation composites, water‐vapor transport diagnostics, and hydroclimatic observations, we identify a transition from historically dominant cold‐dry and cold‐wet winters toward warm‐dominated regimes since the early 2000s, with warm‐dry events exhibiting the strongest increase. Composite geopotential height anomalies reveal persistent mid‐tropospheric ridging during warm‐dry winters, while integrated water vapor transport indicates moisture diversion rather than enhanced convergence. These circulation‐driven compound extremes are associated with widespread snow depth reductions, soil moisture depletion, and suppressed or redistributed runoff, consistent with a multi‐decadal shift from storage‐dominated to flux‐limited winter hydrology.