Modelling the geomorphological impact of climatic variability and extreme events in a semi-arid environment

The climate of the Mediterranean is marginal for many of the economic activities upon which the people of the region depend. Part of this marginality stems from the high inter-annual and medium-term variability in climate. This paper examines the impact of climatic variability on hydrology and vegetation cover using the PATTERN ecosystem model. Significant inter-annual and medium-term variability in the components of the hydrological budget and in vegetation properties and process is apparent in the results. An examination of the variability of soil erosion which results from this variable hydrology and vegetation cover, indicates the temporally erratic nature of erosion events, the tendency for most erosion to occur in very few extreme events, and the dynamic response of erosion to climatic variability. The results also indicate the dependence of erosion on the type of vegetation cover and vegetation response to climatic variability. I conclude with the observation that the majority of significant soil erosion events in Castilla La Mancha (CLM)-site of the EFEDA I and EFEDA II research projects-occur as a result of extreme precipitation events rather than slow progressive land degradation. In this way, soil erosion can be a poor indicator of land degradation. Badlands are the relic of past climatic extremes and not necessarily an indicator of present-day desertification. (C) 1998 Elsevier Science B.V. All rights reserved.