LARGE SCALE PROBABILISTIC DROUGHT CHARACTERIZATION OVER EUROPE

Probabilistic characterization of drought events can play a key role within a drought risk analysis, since it enables the evaluation of drought hazard over a region, which is a preliminary step to drought risk assessment. Besides, the reliable assessment of drought return periods is essential to help decision makers in setting effective drought preparedness and mitigation tools. Generally, an inferential approach (i.e. fitting parametric distributions to observed drought characteristics) is unsuitable to model the marginal or joint probability distributions of drought characteristics, such as drought duration and accumulated deficit, due to the relatively limited number of drought events that can be observed from the historical records of hydrological variable of interest. As an alternative, the marginal and multivariate probability cdf’s of drought characteristics can be derived as functions of the parameters of the cdf of the underlying variable (e.g. precipitation), whose sample series is usually long enough to get reliable results in a statistical sense. In this study, the latter methodology is applied to investigate the space-time variability of drought occurrences over Europe by using the CRU TS3.1 precipitation dataset for the period 1901-2009, which is produced by the British Atmospheric Data Centre through a software provided by the Climate Research Unit (CRU) at the University of East Anglia. First, a spatial analysis of historical droughts at European level is carried out. Then, based on the cdf’s of drought characteristics analytically derived, the return periods of both historical and design drought events are computed as the expected value of the interarrival time between consecutive critical droughts, and the corresponding spatial distribution are investigated. Results show that several heavy drought episodes have widely affected the continent. Among the most recent events, drought occurred during the period 1985-1995 was the worst in terms of extent of the regions characterized by drought return periods greater than 250 years. Besides, Euro-Mediterranean regions, North Western regions (e.g. from Southern England to Germany) and Central Eastern regions (e.g. countries close to the Black Sea) appear more drought prone than the rest of Europe, in terms of low values or return periods.