Spatial distribution of seasonal rainfall trends in a western Mediterranean area

Changes in seasonal patterns of rainfall are key ecological factors. The de finition of the spatial scale on which these changes can occur is particula rly relevant in Mediterranean areas, where problems related to the variabil ity of the pluviometric regime vary from one place to another. The region o f Valencia is a good example of this kind of variability in rainfall regime s. 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 an alysis 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 or der to define subregional areas with similar rainfall evolution. Our result s show a high spatial heterogeneity in rainfall evolution. The striking fea ture is the progressive dryness in the autumn season accompanied by an incr ease 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 Soc iety.