Future upstream water consumption and its impact on downstream availability in the transboundary Indus basin

Abstract. The densely populated plains of the lower Indus basin largely depend on water resources originating in the mountains of the upper Indus basin. Although recent studies have improved our understanding of this upstream-downstream linkage and the impact of climate change, water use in the mountainous part of the Indus has been largely ignored. This study quantifies the comparative impact of upper Indus water usage on downstream water availability under future climate change and socio-economic development. Future water consumption and relative pressure on water resources vary greatly between upper Indus sub-basins and seasons. During the dry season, the share of surface water required within the upper Indus is high and increasing, and in some sub-basins future water requirements exceed availability during the critical winter months. In the lower Indus this causes spatiotemporal hotspots to emerge where seasonal water availability is reduced by over 25 % compared to natural conditions. This plays an important, but previously not accounted for, compounding role in the steep decline of per capita seasonal water availability in the lower Indus in the future due to downstream population growth. Increasing consumption in the upper Indus may thus locally lead to water scarcity issues, and increasingly be a driver of downstream water stress during the dry season. The quantified perspective on the evolving upstream-downstream linkages of the transboundary Indus basin, provided in this study, highlights that long-term water management here must account for rapid socio-economic change in the upper Indus and anticipate increasing upstream-downstream water competition between riparian states.