Water security assessment in mountainous regions: A new framework for integrating water quality and ecosystem service flows

Yunnan Province, a typical mountainous region in southwestern China, acts as a vital water source and ecological barrier for China as well as South/Southeast Asia. However, the province faces growing water security threats from intensifying extreme weather, increasing human water demand, and persistent water quality challenges. To address these issues, this study developed a comprehensive water security assessment framework integrating water quality constraints and water-related ecosystem services (WES) flows. Applying this framework, we systematically evaluated the spatiotemporal dynamics of water security in Yunnan Province from 2000 to 2023. Key findings indicate that: (1) The framework evaluates the level of Effective Water Yield (EWY) services by integrating the Comprehensive Water Quality Index (CWQI), providing an accurate characterization of water security in mountainous regions; (2) The influence of water quality on EWY has increased significantly. EWY accounted for approximately one-third of total water yield (WY), and its decline rate (about −2.05 %/a) exceeded that of total WY (about −1.49 %/a); (3) WES inflow effectively mitigated water stress in an average of 37.83 % of static water security-deficit areas annually; (4) Although Yunnan Province’s dynamic water security was generally dominated by high surplus, approximately 15 % of its regions remained in deficit; (5) Average potential evapotranspiration (APet), average temperature (ATmp), and average precipitation (APre) were the dominant climatic drivers of water security variations in Yunnan Province, collectively accounting for 56.19 % of the relative contribution. These findings provide a theoretical foundation for developing more scientifically robust and effective water security mitigation strategies to assist Yunnan Province in responding to future water security risks.