Impacts of climate, cryosphere and vegetation changes on blue and green water in the Qinghai-Tibetan Plateau.

The Qinghai-Tibetan Plateau is experiencing pronounced warming and wetting, which are reshaping regional hydrological regimes. However, the systemic impacts on blue and green water resources remain insufficiently understood. This study integrates hydrological modeling and machine learning to quantify how warming and wetting, vegetation greening, and cryosphere degradation drive changes in blue and green water in the source region of the Yangtze River. Results show that blue and green water resources increased by 37% and 10%, respectively, in the basin from 1982 to 1998 to 1999-2022. Precipitation increase dominates the blue water increase, contributing 85.2%; the green water increase is jointly driven by precipitation increase and temperature rise, with contributions of 57.2% and 30.8%, respectively. Vegetation greening decreases blue water and increases green water by enhancing evapotranspiration. Cryosphere degradation, including snowmelt increase and thickening of the active layer, contributes positively to both blue and green water. Notably, despite upward trends in blue and green water, the green water coefficient declines, indicating a shift in the regional water resource structure. This transition may enhance basin water conservation capacity and temporarily increase downstream water supply, yet it could raise downstream flood risk and promote swamping of alpine meadows over longer horizons. The findings clarify mechanisms governing water cycle evolution on the Tibetan Plateau under concurrent environmental changes and provide a scientific basis for regional water resource management.