The feasibility and potential impact of an inter-basin water transfer project can be evaluated, under a changing environment, by employing the coincidence probability of runoff in water sources area (WSA), water receiving area (WRA) and the downstream impacted area (DIA). Using the Han River to Wei River Water Transfer Project (HWWTP) in China as an example, this paper studied the coincidence probability and conditional probability of runoff in WSA, WRA and DIA by the copula-based multivariate joint distribution and qualified their acceptable and unfavorable encounter probabilities for evaluating water supply risk of the water transfer project and exploring its potential impact on DIA. Results demonstrated that the most adverse encounter probability (dry–dry–dry) was 26.09%, illustrating that this adverse situation could appear about every 4 years. The acceptable and unfavorable probabilities in all encounters were 44.83 and 55.17%, respectively, and the unfavorable situation could be dominant, implying flood and drought risk management should be paid greater attention in project operation. The conditional coincidence probability (dry WRA & dry DIA if dry WSA) was close to 70%, indicating a requirement in an emergency plan and management to deal with potential drought risk.
Coincidence probability of annual runoff in all main impacted areas is investigated.
Copula-based method to capture the encounter situations of water transfer project.
Acceptable and unfavorable probabilities in all encounters imply water transfer risk.
Conditional coincidence probability with dry water resources area was computed.
An emergency water scheduling plan is required to deal with potential drought risk.