The Gaussian copula model for the joint deficit index for droughts
Van de Vyver, Hans
Van den Bergh, Joris
Earth and related Environmental sciences
Drought; Joint deficit index; Gaussian copula; Geostatistics
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The characterization of droughts and their impacts is very dependent on the time scale that is involved. In order to obtain an overall drought assessment, the cumulative effects of water deficits over different times need to be examined together. For example, the recently developed joint deficit index (JDI) is based on multivariate probabilities of precipitation over various time scales from 1- to 12-months, and was constructed from empirical copulas. In this paper, we examine the Gaussian copula model for the JDI. We model the covariance across the temporal scales with a two-parameter function that is commonly used in the specific context of spatial statistics or geostatistics. The validity of the covariance models is demonstrated with long-term precipitation series. Bootstrap experiments indicate that the Gaussian copula model has advantages over the empirical copula method in the context of drought severity assessment: (i) it is able to quantify droughts outside the range of the empirical copula, (ii) provides adequate drought quantification, and (iii) provides a better understanding of the uncertainty in the estimation.
Van de Vyver, H.; Van den Bergh, J. The Gaussian copula model for the joint deficit index for droughts. J. Hydrol. 2018, 561, 987–999.