Spatiotemporal imbalance of regional water shortage risk based on copulas and concentration index

Water resources are essential for human survival and development. Ensuring sufficient water supply to meet living, production, and ecological demands has emerged as a critical challenge for regions facing water scarcity. In response to the increasingly severe water shortage in Central Yunnan, the Chinese government has invested over 100 billion yuan in implementing the Central Yunnan Water Diversion Project (CYWDP). Accurately assessing and predicting the project’s impact on water shortage risk and its spatiotemporal imbalance in the receiving regions is crucial for fostering sustainable and high-quality regional development. In this study, we propose an integrated methodological framework that combines Copula functions with a concentration index to evaluate the effects of the CYWDP on water shortage risk and its spatiotemporal imbalance in the Yuxi water-receiving area. First, based on risk theory, we develop a water shortage risk assessment model by integrating Kernel Density Estimation (KDE) with Copula functions to evaluate water shortage risk under various scenarios. This model accounts for the heterogeneous importance of domestic, industrial, agricultural, and ecological water uses. Second, a simplified concentration index is introduced to quantify the spatiotemporal imbalance of water shortage risk. The results reveal that: (1) Water shortage risk in the Yuxi water-receiving area exhibits strong seasonality, with spring being the highest-risk period, in approximately 80% of years falling into moderate-risk zones. Interannual variability in risk is high and strongly negatively correlated with precipitation, and only in wet years can water supply security be effectively ensured. (2) Due to differences in precipitation, groundwater availability, and the number of water storage projects, sub-regions display heterogeneous distributions of water shortage risk, with significant spatial imbalance. Intra annual variations are also evident, and more pronounced in dry years compared with wet years. (3) Without considering the supplemental supply from the CYWDP, the receiving area is projected to enter a high-risk zone by 2030 and 2040. However, with the CYWDP, the overall risk is expected to decrease to a moderate level by 2030, and by 2040, increased water transfers could alleviate risks and mitigate spatial imbalances. This study provides critical insights for evaluating the socio-economic benefits of the CYWDP and offers guidance for water resource allocation strategies. Moreover, the proposed framework serves as a methodological reference for analogous studies.