Daily rainfall patterns in the Spanish Mediterranean area: an objective classification

Using a 30-year data base of daily precipitation at 410 sites of Mediterranean Spain, the main spatial patterns controlling significant and ‘torrential’ daily rainfalls in the area are derived. This is done by applying cluster analysis on the most relevant principal directions extracted from a principal components analysis of the between-day correlation matrix. Seasonal and decadal frequency distributions of the emergent rainfall patterns as well as their principal interlinks are presented and discussed. Despite the large proportion of convective rainfalls in the area, the clusters obtained are quite definite and clearly display the dominant role exerted by the complex topography and its connection with the main rain bearing flows. Patterns for significant rainfalls and those for the subgroup of torrential days display very similar spatial characteristics, meaning that rainfalls are similarly highly structured regardless of their type, and strongly linked to the topography. Nevertheless, a certain tendency of enhancing the importance of coastal zones for torrential events is observed. Plots of interseasonal variability reveal a different incidence of significant and torrential rainfall patterns through the year. The western patterns, largely stimulated by Atlantic flows, show peak frequencies in winter for total rainfalls, but similar incidence in winter and autumn for torrential events. On the contrary, the eastern patterns, which are strongly influenced by the Mediterranean dynamics, exhibit a diversity of behaviors for the general case depending on the zone, but they all dominate in the fall season for the torrential case.