A decision-oriented multivariate copula framework for assessing wet–dry encounters and hydrological compensation potential in interbasin systems: a case study of Jiangsu, China

The interaction between the Yangtze River and Huaihe River Basins plays a critical role in regional water security under interbasin water-resource systems. However, existing studies rely primarily on bivariate or single-basin analyses and rarely address how multivariate dependence structures influence hydrological compensation potential from a source-receiving perspective. In this study, a decision-oriented multivariate framework is proposed to quantify wet-dry encounter patterns and the estimated probability by explicitly linking upstream runoff and regional precipitation. A three-dimensional C-vine copula model is constructed using precipitation and runoff data from 1968 to 2024 for the Yangtze River (Datong Station), the Huaihe River (Wujiadu Station), and three subregions of Jiangsu Province. The results reveal distinct dependence structures across regions, with upper-tail dependence characterizing the Datong-Sunan system and more symmetric dependence patterns observed in the Wujiadu-Huaibei and Datong-Wujiadu pairs. A detrending-based sensitivity analysis indicates that the significant increasing trend in Sunan precipitation does not substantially alter the main Datong-Sunan dependence pattern. Under dry receiving-region conditions, the joint probabilities that at least one upstream source remains wet or normal are 0.23 for Huaibei and 0.22 for Sunan, corresponding to conditional hydrological compensation potentials of 62.2% and 62.9%, respectively. These values should be interpreted as theoretical hydrological source-availability indicators rather than direct operational water-diversion feasibility. This study provides a transferable probabilistic approach for assessing wet-dry encounter risks and the estimated probability in multisource water-resource systems.