Iran’s multivariate drought frequency analysis based on novel heterogeneous and homogeneous archimedean copula structuresIran’s multivariate drought frequency analysis based on novel heterogeneous and homogeneous archimedean copula structuresR. Alizadeh-Sh et al.

Drought is a multivariate and complex phenomenon that spreads over vast areas. Without a comprehensive drought plan, drought events can become disasters, causing significant socio-economic and environmental damage. Drought frequency analysis is crucial for developing water resource management plans to mitigate drought impacts. Copulas are powerful mathematical tools for constructing a multivariate joint dependence structure using correlated variables. This study utilized a novel heterogeneous-asymmetric copula structure approach alongside other standard copula models. This model was applied in Iran’s first- and second-degree basins and country extent from 1986 to 2021, using Duration, Severity, Peak, and Interarrival time to perform multivariate drought frequency analysis with conjunction, disjunction, and conditional logical operations cases. Based on the goodness-of-fit test results of the four-variate models, heterogeneous-asymmetric structures accounted for 29.2% of the joint distribution structures. This case highlights the importance of employing these novel copula structures to improve joint behavior modeling accuracy. The most severe drought in the CS-6 basin had a four-variate return period of 142.6 and 16.6 years in the conjunction and disjunction cases, respectively. This study's results highlight the importance of considering all four drought characteristics simultaneously and jointly for drought frequency analysis.