Abstract:
This research study was carried out to investigate the characteristics of drought based on the
joint distribution of two dependent variables, the duration and severity, in the Eastern Cape Province,
South Africa. The drought variables were computed from the Standardized Precipitation Index for
6- and 12-month accumulation period (hereafter SPI-6 and SPI-12) time series calculated from the
monthly rainfall data spanning the last five decades. In this context, the characteristics of climatological
drought duration and severity were based on multivariate copula analysis. Five copula functions
(from the Archimedean and Elliptical families) were selected and fitted to the drought duration
and severity series in order to assess the dependency measure of the two variables. In addition,
Joe and Gaussian copula functions were considered and fitted to the drought duration and severity
to assess the joint return periods for the dual and cooperative cases. The results indicate that the
dependency measure of drought duration and severity are best described by Tawn copula families.
The dependence structure results suggest that the study area exhibited low probability of drought
duration and high probability of drought severity. Furthermore, the multivariate return period
for the dual case is found to be always longer across all the selected univariate return periods.
Based on multivariate analysis, the study area (particularly Bu alo City, OR Tambo and Alfred Zoo
regions) is determined to have higher/lower risks in terms of the conjunctive/cooperative multivariate
drought risk (copula) probability index. The results of the present study could contribute towards
policy and decision making through e.g., formulation of the forward-looking contingent plans for
sustainable management of water resources and the consequent applications in the preparedness for
and adaptation to the drought risks in the water-linked sectors of the economy.
