Decreased precipitation intensifies hydrological drought in the largest river basin of the Tibetan Plateau

The Yarlung Zangbo (YZ) basin, the largest river basin on the Tibetan Plateau, is a climatically complex international river that plays a critical role in regional water security while facing a high risk of extreme hydrometeorological drought. Hydrological droughts in cryospheric basins are governed by interactions between climate variability and glacier processes, yet their dominant drivers remain poorly constrained. This study combines the VIC-Glacier model with explainable machine learning techniques (XGBoost/RF coupled with SHAP) to investigate hydrological droughts during 1998–2020 and to quantify the relative contributions of climatic, cryospheric, and large-scale atmospheric drivers. Results revealed pronounced spatial heterogeneity in drought characteristics across YZ sub-basins. The upstream Nuxia (NX) basin experienced intensified meteorological drought (-0.04 per decade), with droughts concentrated in winter and spring. In contrast, the downstream NX-BXK sub-basin exhibited spatially extensive, multi-seasonal droughts despite higher glacier coverage, indicating strong hydrological sensitivity to precipitation variability. Hydrological droughts showed clear amplification relative to meteorological droughts, with greater severity and duration, particularly in the NX-BXK sub-basin where runoff declines exceeded precipitation reductions. Attribution results identify the Arctic Oscillation as the dominant driver (30–35%), followed by precipitation anomalies and precipitation-induced runoff. Glacier runoff played a minor role in drought occurrence (<5%) but reduced drought severity by 10–36% during drought events. • A process-based framework for hydrological drought dynamics using hydrological modeling and explainable ML. • Hydrological droughts showed greater severity and duration than meteorological droughts due to amplified runoff responses. • Strong sub-basin heterogeneity was observed, with winter–spring droughts in NX and multi-season droughts in NX–BXK. • Hydrological droughts were mainly driven by the AO, while glacier runoff played a minor role.