Evaluating future water security in the upper Yangtze River Basin under a changing environment

Water security is of great significance in social development, ecosystem sustainability, and environmental management. The Upper Yangtze River Basin (UYRB), which feeds more than 150 million people, is faced with aggravating water security risks due to more frequent hydrometeorological extremes and increasing human water withdrawals under a changing environment. Based on five RCP-SSP scenarios, this study systematically evaluated the spatiotemporal evolution patterns of water security in the UYRB under future climatic and societal changes. The future runoff was projected using Watergap global hydrological model (WGHM) under different Representative Concentration Pathway (RCP) scenarios and hydrological drought was further identified by the run theory. The water withdrawals were predicted based on the recently developed shared socio-economic pathways (SSPs). Then, a comprehensive risk index (CRI) for water security was proposed combining the degree of water stress and natural hydrological drought. The results show that the future annual average runoff across the UYRB is projected to increase, and hydrological drought tends to be more severe, especially in the upper and middle reaches. Dominated by water withdrawals in the industry sector, the future water stress in all sub-regions is estimated to increase substantially, with the largest change ratio of WSI in the middle future spatially ranging from 64.5 % to 301.5 % (66.0 % to 314.1 %) under RCP2.6 (RCP8.5). Based on the spatiotemporal variation of CRI, the UYRB is projected to face more severe comprehensive risks for water security in the middle and far future periods, and hotspot sub-regions are identified as Tuo River and Fu River, which are densely populated and economically prosperous, threatening regional sustainable social-economic development. These findings highlight the urgent need for adaptive countermeasures of water resources administration in response to more severe water security risks in the future UYRB.