Intensified water scarcity in the Asian Water Tower driven by increased water withdrawals

The Asian Water Tower (AWT), encompassing the Tibetan Plateau and surrounding mountain ranges, provides water for nearly 2 billion people. It spans transboundary basins such as the Indus, Ganges-Brahmaputra, and Mekong, with notable variability in water resources. This study investigates the spatiotemporal dynamics of water availability and withdrawals during 1980–2022 using the PCR-GLOBWB v2.0 model. Water scarcity dynamics are examined across multiple spatial and temporal scales, and key drivers of change are identified. The long-term average annual water availability and withdrawal are 1211 km³ and 545 km³ , respectively. A cross-basin comparison reveals significant heterogeneity in water stress patterns, with scarcity concentrated in the lower parts of the catchment, particularly in the downstream regions of the Indus and Ganges-Brahmaputra basins. The water stress index has increased over past four decades, especially during the wet season (May to October). Although downstream water availability increased by 96 km³ between 1980–2000 and 2001–2022, withdrawals increased by 152 km³ , resulting in persistent water shortages. Downstream irrigation is the dominant driver of water scarcity in most basins, while upstream runoff influence wet season scarcity in some basins. By comparing eight major basins under a consistent analytical framework, this study identifies basin-specific variability in water scarcity drivers, and highlighting the structural dominance of downstream demand across the AWT. • Annual water availability and withdrawal are 1211 km 3 and 545 km 3 in the Asian Water Tower, with high spatial variability. • Water scarcity is concentrated in the lowermost parts of the basin and during the dry season. • Water scarcity has become more severe from 1980 to 2022 mainly due to increased downstream irrigation withdrawal. • Over 60 % of the population is exposed to severe water scarcity.