Drought Analysis Based on Copulas

Droughts produce a complex set of negative economic, environmental, and social impacts across a country or region. Using monthly standardized Precipitation Index (SPI) values, drought characteristics, namely, drought duration, severity, interval time and minimum SPI values, were determined. Two exponential distributions were used to model drought duration and interval time, respectively; gamma distribution was used to model for drought severity; and generalized Pareto distribution to model minimum SPI value. Several copulas in the Archimedean and meta-elliptical families were applied to construct fourdimensional joint distributions. The upstream Han River basin was selected as an example to illustrate the copulas. Results indicates that the Student copula was more appropriate for drought analysis in the selected area. Drought probabilities and return periods were calculated and analyzed based on the fourdimensional copula.