Jordan Journal of Civil Engineering

Bivariate Frequency Analysis of Hydrological Drought Using Copula: A Case Study of Northern Iraq


IHSAN HASAN; Rozi Abdullah; Taymoor Awchi;


In this paper, Copula based methodology is adopted to analyze the hydrological drought frequency, Standardized Runoff Index SRI was calculated using monthly streamflow data for 50 year period of two gauging stations in the northern region of Iraq. The drought characteristics (duration and severity) were extracted based on run theory. Three Archimedean family and Gaussian copulas were used and compared to select the most appropriate copula model for bivariate frequency analysis of hydrological drought characteristics. The dependence between the drought duration and severity was estimated by Pearson's correlation, Kendall's tau, and Spearman's rho. Various probability distribution functions were used to determine the best fit marginal distributions for drought characteristics variables based on the Kolmogorov-Smirnov and Chi-Squared statistics. Univariate and bivariate return periods were calculated and compared. Generally, the results indicate that Archimedean copulas performed better than Gaussian copula. Exponential and Weibull distributions are the best fit distributions for drought duration and severity, respectively, except for drought severity in case of the 12-month time scale at Lesser Zab region, Lognormal distribution was chosen. This study can provide useful information for drought risk assessment and water resources management under climate change.


Hydrological drought; Copula, SRI, Greater Zab River; Bivariate return periods.