Climate Change, Desertification and the Mediterranean Region

Abstract

Land desertification, a series of natural processes leading to gradual environmental degradation, is now considered as a serious threat to the semi-arid areas of the Mediterranean, and particularly to the marginal hilly lands of the region. Soil erosion comprises the dominant process of land deterioration and desertification. Adverse climatic conditions, irregular terrain with steep slopes, geology and long periods of land misuse are the main factors responsible for desertification in the Mediterranean. The climate of the region is characterised by strong seasonal and spatial variations in rainfall and large oscillations between minimum and maximum daily temperatures. Moreover, higher temperatures and more pronounced aridity are predicted to prevail during the next decades. The extensive deforestation and intensive cultivation of sloping lands since ancient times has already led to soil erosion and degradation through the progressive inability of the vegetation and soils to regenerate themselves. Hilly soils developed on Tertiary and Quaternary formations usually have a restricted effective rooting depth for plant growth. Under hot and dry climatic conditions, the tolerance of these soils to erosion is low, and rainfed vegetation can no longer be supported. Many areas on limestone formations are already desertified with the soil mantle eroded and the vegetation cover completely removed. For example, soils formed on marl deposits, despite their considerable depth and high productivity in normal and wet years, are very susceptible to desertification in dry years. Intensive human interference in hilly areas vulnerable to desertification has severely damaged or totally destroyed the productivity of these lands due to the loss of soil volume beyond a critical point.