Enhanced Internal Moisture Redistribution Drives Summer Wetting over the Inner Tibetan Plateau Since the 1990s

Summer precipitation over the inner Tibetan Plateau (TP) has increased markedly since the 1990s, leading to widespread lake expansion and exerting profound impacts on local ecosystems and infrastructure. By integrating an Eulerian moisture back-tracking model (Water Accounting Model: WAM-2layers) with large-scale circulation diagnostics for 1979–2021, we find that intensified internal moisture redistribution plays a more prominent role in driving the wetting trend compared to changes in external moisture transport or local evaporation. Specifically, the eastern TP (ETP) has emerged as the dominant contributor, with its moisture supply increasing by 7.01 mm mon-1 (22.4%) since 1999, accounting for 36.7% of the total precipitation increment (19.10 mm mon-1). This contribution exceeds those from both southern and western external sources. Notably, this enhanced ETP contribution is driven by anomalous easterly winds rather than local thermodynamic factors. This shift coincides precisely with the interdecadal regime transition of the Silk Road Pattern (SRP) from a positive to a negative phase around 1998/1999. The negative SRP phase anchored an anomalous anticyclone to the north flank of the TP, triggering the robust low-level easterly anomalies that redirected moisture from the ETP westward into the inner TP. These results highlight that intensified internal water recycling is a major mechanism reshaping the regional hydrological balance and accelerating lake expansion in the inner TP.