Droughts produce a complex set of negative economic, environmental, and social impacts from regional to national scales. The drought impact can be quantified using drought index time series. This study uses the monthly standardized precipitation index (SPI) time series as a drought index. Drought characteristics, namely, drought duration, severity, interval time and minimum SPI values, were determined. Five hundred years of daily rainfall data were simulated for evaluating drought characteristics. Appropriate distributions were selected for modeling drought duration, interval time, drought severity, and minimum SPI value in different drought states. The drought episodes were quantified using multivariate copula methods. Several copulas from the Archimedean and metaelliptical families were applied to construct four-dimensional joint distributions. The dependence structure in each drought state was investigated and drought probabilities and return period were calculated and analyzed based on a four-dimensional copula using the upper Han River basin, China, as a study area. 2013 American Society of Civil Engineers.
