Coincidence Risk Analysis of Annual Runoff and Sediment Using Archimedean

In recent years, frequently-happened flood and sediment disaster accidents can cause significant damage to basin economic and social development. In this paper, the coincidence risks of annual runoff and sediment yield on Jinsha River in China were analyzed using multivariate copulas. The marginal distributions of annual runoff and sediment yield were fitted by the P-III distribution from observed data. The situations of annual runoff and sediment yield were classified into rich, normal and poor states by the exceedance probabilities of 25%, 50% and 75%, respectively. Archimedean Copulas were selected to establish the joint cumulative distribution function (CDF) of annual runoff and sediment yield. The synchronous-asynchronous coincidence probabilities of different combinations of annual runoff and sediment were investigated. The joint return periods in “OR” and “AND” cases derived based on the established joint CFD were also computed and compared. Results show that the Gumbel-Hougaard Copula is the most appropriate for modeling the joint distribution of annual runoff and sediment yield. The sum of synchronous coincidence probabilities for annual runoff and sediment is 63.78%, which is much greater than that of asynchronous coincidence probabilities. The maximal coincidence probability is the synchronous coincidence probability of annual normal runoff and normal sediment, with the value of 36.76%. The minimal coincidence probability is the asynchronous coincidence probability of annual rich runoff and poor sediment or annual poor runoff and rich sediment, with the value of 1.62%. This indicates a better correlation between annual runoff and sediment yield on Jinsha River. In addition, the joint OR return period of annual runoff and sediment is lower than their univariate return periods, and the joint AND return period is higher than their univariate return periods. This study can provide technological support for risk assessment of annual runoff and sediment yield in the Jinsha river basin.