Changes in seasonal precipitation in the Iberian Peninsula during 1946–2005

The spatial variability of seasonal precipitation regimes in the Iberian Peninsula is overlapped by complex patterns of temporal variability. Consequently, traditionally described space domains of seasonal rainfall regimes in Spain may be changing. In this paper we evaluate seasonal precipitation trends over Spanish conterminous land to determine how these trends are modifying traditionally described seasonal rainfall regimes in the study area. To this end, we used a recently developed high resolution grid (1/10 degree longitude and latitude) derived from the MOPREDAS database, comprising 2670 complete and homogeneous monthly precipitation series for the 1946–2005 period, and calculated and compared the seasonal precipitation regimes observed in two consecutive 30-year periods (1946–1975 and 1976–2005). We found that, from the total of 24 possible permutations between winter, spring, summer and autumn as dominant and subdominant precipitation seasons, 12 coexist over Spanish conterminous land. Moreover, there have been notable changes in the last 30 years, affecting not only the most prominent season, but also the variant within each regime. The trends observed therefore indicate that, on comparing the two 30-year subperiods, the percentage of territory in which winter constitutes the dominant precipitation season decreases from 51.1% to 42.7% of the total study area. Similarly, spring was the dominant precipitation season in 36.1% of the territory in the 1946–1975 period, whereas in the 1976–2005 period, it is the dominant one in less than half (15.1%) the territory. This contrasts with areas where autumn constituted the main precipitation season, which increased from 10.8% (restricted to the Mediterranean coast) to 41.4% of the territory. Within the context of climate change, these variations among seasonal precipitation patterns can be explained by (1) a subtropicalization of the IP climate with a reduction of rainfall amounts from winter to summer and (2) an increase in the autumn rainfall percentage.