Multivariate regional frequency analysis: Two new methods to increase the accuracy of measures

•Regional distribution parameters are estimated using the optimization-based method.•The rank-based method is proposed for determining the robust discordancy measure.•The proposed methods improve the performance of the heterogeneity measure. The accurate detection of discordant sites in a heterogeneous region and the estimation of the regional parameters of a statistical distribution are two important issues in multivariate regional frequency analysis. In this study, two new methods are proposed for increasing the accuracy of the multivariate l-moment approach. The first one, the optimization-based method (OBM) is utilized to estimate the best distribution parameters. The second one is the rank-based method (RBM), which is used in the robust discordancy measure for identifying discordant sites. In order to assess the performance of the proposed approaches on the heterogeneity measure, real and simulated regions of drought characteristics are considered. The results confirm the usefulness of the new methods in comparison with some well-established techniques.