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In order to understand the behaviour of ecosystems in semi-arid areas, rainfall must be analysed over time. For this reason, statistical methods were applied to a rainfall time-series (1967-1997) in a typical Mediterranean semi-arid area in SE Spain of great ecological interest. Annual, seasonal and monthly time scales were studied, including rainfall volume, number of rain-days and one-day maximum rainfalls. Results showed neither trends nor abrupt changes in the series, although three periods, averaging 301, 183 and 266 mm year(-1) respectively were observed from fluctuation in rainfall. Modal values of annual and monthly rainfalls were lower than average. Inter-annual variability was 36% and intra-annual variability up to 207%. Although there was often a rainfall maximum in autumn and a minimum in July, the only certainty was a summer drought, which marking strong annual cycles. The estimated return periods for events of more than 50, 70 and 100 mm day(-1) were over 5, 11 and 30 years respectively; the absolute maximum 1-day rainfall recorded was 98 mm. Results suggest that vegetation is not only adapted to the amount of precipitation, but also to its timing. All types of rainfall, in terms of volume and timing, would have consequences for vegetation. (C) 2001 Academic Press.