After computing the value of Di at each station, the results were then processed using the SPEI R package to determine the SPEI at various time intervals. The SPEI R package may be accessed at http://cran.r-project.org/web/packages/SPEI. Di was fitted using the logarithmic distribution function f(x) in Equation (3). The SPEIs were derived from numerous time series, including SPEI-1, SPEI-3, SPEI-6, and SPEI-12, using Equation (4):