Coincidence Risk Analysis of Floods Using Multivariate Copulas: Case Study of Jinsha River and Min River, China

The coincidence of floods on a mainstem and its tributaries may cause significant flood damage downstream of the confluence. In this study, the coincidence risks of annual maximum (AM) floods on Jinsha River and Min River, China, were analyzed using multivariate copulas based on both systematic records and available historical information. Archimedean and elliptical copulas were selected to establish the joint distributions of flood magnitudes and occurrence dates of the two rivers. The coincidence probabilities of AM floods were investigated and compared with monthly maximum floods. The results show that the coincidence probabilities of AM flood magnitudes and occurrence dates are much less than those of monthly maximum floods. Higher coincidence probabilities of AM flood occurrence dates occur in the period from mid-June to early September with three coincidence peaks, while there is only one coincidence peak in each month for monthly maximum floods. Ignoring historical flood information would underestimate the coincidence probabilities of flood magnitudes. The results can provide decision support for cascade reservoir operation on Jinsha River and flood mitigation downstream.