Analysis of a 30-year rainfall record (1967-1997) in semi-arid SE Spain for implications on vegetation

In order to understand the behaviour of ecosystems in semi-arid areas, rain fall must be analysed over time. For this reason, statistical methods were applied to a rainfall time-series (1967-1997) in a typical Mediterranean se mi-arid area in SE Spain of great ecological interest. Annual, seasonal and monthly time scales were studied, including rainfall volume, number of rai n-days and one-day maximum rainfalls. Results showed neither trends nor abr upt changes in the series, although three periods, averaging 301, 183 and 2 66 mm year(-1) respectively were observed from fluctuation in rainfall. Mod al values of annual and monthly rainfalls were lower than average. Inter-an nual 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 onl y certainty was a summer drought, which marking strong annual cycles. The e stimated return periods for events of more than 50, 70 and 100 mm day(-1) w ere over 5, 11 and 30 years respectively; the absolute maximum 1-day rainfa ll 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 rainfa ll, in terms of volume and timing, would have consequences for vegetation. (C) 2001 Academic Press.