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Philippe Naveau, Laboratoire des Sciences du Climat et de l'Environnement, IPSL-CNRS, France

Detecting changes in multivariate extremes from climatological time seriesÌý

Joint work with Sebastian Engelke (Geneva University) and Chen Zhou (Erasmus University Rotterdam)Ìý

Many effects of climate change seem to be reflected not in the mean temperatures, precipitation or otherÌýenvironmental variables, but rather in the frequency and severity of the extreme events in the distributionalÌýtails. The most serious climate-related disasters are caused by compound events that result from an unfortunateÌýcombination of several variables. Detecting changes in size or frequency of such compound events requires aÌýstatistical methodology that efficiently uses the largest observations in the sample.

We propose a simple, non-parametric test that decides whether two multivariate distributions exhibit the same tail behavior. The test isÌýbased on the entropy, namely Kullback–Leibler divergence, between exceedances over a high threshold of theÌýtwo multivariate random vectors. We study the properties of the test and further explore its effectiveness forÌýfinite sample sizes.Ìý

Our main application is the analysis of daily heavyÌý rainfall times series in France (1976 -2015). Our goal in this application is to detect if multivariateÌý extremal dependence structure in heavy rainfall change according to seasons and regions.Ìý