Climate change affects the water supply of the Chinese Water Tower

Mountain regions function as natural “water towers” by storing water and supplying it to downstream areas. The source regions of the Yellow, Yangtze, and Lancang-Mekong rivers on the eastern Tibetan Plateau are referred to as the “Chinese Water Tower,” providing freshwater to billions of people across downstream China and Southeast Asia. A cryospheric meltwater tracking hydrological model is developed to simulate hydrological changes as well as variations in snow, permafrost, and glaciers, and to quantify the runoff contributions of cryospheric meltwater. The results show that historically (1960–2019), cryospheric meltwater contributed 21–32% of the total runoff. Under three future socio-economic pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5), runoff in the three headwater basins is projected to increase during 2020–2100. However, due to substantial cryospheric degradation as indicated by diminishing snow cover, a thickening active layer and declining glacier ice storage, the runoff contribution of cryospheric meltwater is unlikely to be sustainable in a warming climate. Overall, the total contribution of cryospheric meltwater is projected to decline in the Chinese Water Tower, indicating a loss of water storage and regulation capacity, reduced drought mitigation capacity, and weakened interannual runoff stability. Moreover, under different scenarios, the mismatch between population growth and water resources may exacerbate water supply–demand imbalances. This study highlights the widespread risks of declining cryospheric meltwater supply both in the Tibetan Plateau and in other cold-region catchments in a warming climate.