Spatial distribution of seasonal rainfall trends in a western Mediterranean area

Changes in seasonal patterns of rainfall are key ecological factors. The definition of the spatial scale on which these changes can occur is particularly relevant in Mediterranean areas, where problems related to the variability of the pluviometric regime vary from one place to another. The region of Valencia is a good example of this kind of variability in rainfall regimes. To study changes in seasonal means and variability, we have applied non-parametric (Spearman test) and parametric techniques (linear model) to data from 97 pluviometric stations during the World Meteorological Organization (WMO) normal period, 1961-1990. Special emphasis has been placed on the analysis of the spatial pattern of trends in means and variability. For this purpose, Ne have used a modified version of the Cramer-von Mises test in order to define subregional areas with similar rainfall evolution. Our results show a high spatial heterogeneity in rainfall evolution. The striking feature is the progressive dryness in the autumn season accompanied by an increase in interannual variability. Increases in winter and summer interannual variability, and decreases in rainfall amounts in winter are dominant too. We discuss these results in relation to rainfall generation mechanisms and their ecological implications. Copyright (C) 2001 Royal Meteorological Society.