Abstract: This study addressed the water supply risks in the receiving areas of the middle route of the South-to-North Water Transfer Project, which arose from varying drought-wetness encounters of runoff between the water supplying and receiving areas.A Copula-based joint probability distribution model was developed using measured data from representative hydrological stations from 1979 to 2023.The model was used to estimate the probabilities of different runoff encounter conditions.The water availability of the receiving areas was determined through the water dispatching of Danjiangkou Reservoir in the water supplying areas and water allocation in the receiving areas.The resulting water availability was applied to water supply risk assessment.Based on the results of water availability, the water supply risk rate, resilience, and vulnerability were calculated to quantitatively assess the water supply risks in the receiving areas.The results showed that the Gumbel-Hougaard Copula function best fitted the joint distribution of runoff between the supplying and receiving areas.The synchronous encounter probability of runoff in the water supplying and receiving areas was 41.03%.The encounter probabilities for the dry-dry, dry-extreme dry, extreme dry-dry, and extreme dry-extreme dry conditions were 13.53%, 2.36%, 2.36%, and 0.61%, respectively.On average, the transferred water accounted for 19.18%, 27.77%, 27.82%, and 24.65% of the water availability in Henan Province, Hebei Province, Tianjin City, and Beijing City, respectively.The water supply risks in the receiving areas exhibited an upward trend with the decrease in runoff in the water supplying and receiving areas.When both areas experienced extremely dry years, the water supply risk was at a medium level, and it would further increase during consecutive dry years.The research results can provide reference for ensuring the normal operation of the middle route of the South-to-North Water Transfer Project and the optimal allocation of water resources.