Spatial and temporal characterization of annual extreme droughts in Catalonia (northeast Spain)

Several characteristics of annual extreme drought episodes for Catalonia (northeast Spain) are investigated from different points of view. Firstly, possible temporal trends on the length of these episodes are analysed, by means of Student's t test and a Monte Carlo procedure, for each complete pluviometric series. Secondly, the spatial distribution of the seasonal predominance of the annual extreme droughts is analysed, showing the influence of the orographic factors. Thirdly, most of the annual extreme episodes are modelled correctly by the Gumbel distribution of extremes, and the expected lengths for return periods of 2, 5, 10, 25 and 50 years are computed. Nevertheless, some discordances were detected between this theoretical distribution and the empirical extremes. Thus, the return periods for some gauges were computed by means of the more general Jenkinson model. Finally, the set of pluviometric stations are characterized by the extreme drought lengths of the different return periods, and they are classified according to the average linkage algorithm into clusters of homogeneous gauges. In short, the results obtained suggest that most of the country is characterized by a typical Mediterranean behaviour. However, some differences can be established between littoral areas, some parts of the Central Basin and the pre-Pyrenean and Pyrenean ranges.