Hydrological phenomena such as floods and droughts are associated with several dependent characteristics, but most of previous researches have been considered the univariate analysis because of its simplicity (Hao and Singh, 2016). In order to understand the phenomenon of drought more accurately, multivariate analysis of its characteristics seems necessary. Sklar (1959) first proposed the theory of copula functions, which makes multivariate analysis easier than the previous methods. In recent years, multivariate analysis of drought has attracted the attention of researchers (e.g., Ni et al., 2020; Hui-Mean et al., 2019). Multivariate analysis of drought, especially by the vine copula functions, is relatively new both globally and in Iran. Therefore, lack of applied researches in the field of multivariate regional modeling of drought was the main motivation for the present study. Our aim in this study is to use the D-vine copula function to model the dependency structure of drought characteristics.
