Water management requires, among other information, the proper identification of drought events and their characteristics: duration and severity. In this paper we compute standardized runoff index (SRI), which is an index based on runoff but computed following the same methodology as standardized precipitation index, over the Rio Grande basin. The runoff values were generated from the Noah land surface model. The drought duration and severity for each year were extracted and copula was used to

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... roduce the joint probabilities of drought severity and duration. Four copulas were tested and the Gumbel-Hougaard (GH) copula was deemed most appropriate for this dataset. The conditional probability distributions for severity given duration thresholds and duration given severity thresholds were also computed. This information can help water managers assess water availability and plan for extreme events accordingly.