Reframing extreme drought characterization. The super drought concept, index, and web services
Wang, Lin ; Huang, Gang ; Chen, Wen ; Wang, Ting
Super Drought under Global Warming: Concept, Monitoring Index, and Validation
Recent decades have witnessed growing frequency and severity of catastrophic droughts in many regions of the world. Despite lots of studies having been dedicated to extreme drought investigation, the fundamental question that has long been ignored is, What is extreme drought? The answer is much more complex than it first appears, because a critical issue in the study of drought is the multiscalar nature. To address the challenge, this study establishes the theoretical basis of the super drought concept, which refers to the simultaneous occurrence of extreme droughts at multiple time scales. The physical significance of super drought represents compound dry extremes in all parts of water resources or equivalently a grand loss in total water storage, which is identified as the essential determinant distinguishing high-impact droughts from those causing mild damage. To have a quantitative representation, a novel monitoring index called comprehensive multiscalar index (CMI) is developed based on the vine copula framework. It turns out that CMI is a plausible measure to determine the overall rarity of multiscalar drought and recognize super drought. Furthermore, the worldwide skill of CMI and super drought identification are testified against Gravity Recovery and Climate Experiment (GRACE) total water storage. Compared to traditional indices that lack comprehensive treatment of drought, CMI performs better in capturing the variation of overall water availability and enables the accurate detection of real water scarcity, with gross improvements in correlation and root-mean-square error scores exceeding the 10?3 significance level. To facilitate end users and policy-makers, near-real-time monitoring and a historical data repository are available through the public website superdrought.com.</p>
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