Sensitivity of a Sandy Area to Climate Change Along a Rainfall Gradient at a Desert Fringe

Global climate change has become a strongly and frequently addressed issue in the last decades. The aspect is crucial in dry-land areas, which cover approximately one third of the globe's total land area. The relationship between average annual rainfall and environmental variables has attracted the attention of many scientists. Climatologists use aridity indices to express relationships between climatic and environmental variables (Köppen 1931; Budyko 1974; Wallen 1967; Bailey 1979). These indices, based on purely climatic variables such as annual precipitation, temperature, evaporation and radiation, tend to imply that the acuteness of aridity is inversely related to annual precipitation. Although aware that soil water content depends on local soil type and precipitation regime, Walter (1939, 1960) asserted that at a larger, global scale, standing biomass is positively correlated to average annual rainfall. This approach is still followed by many researchers who assume a positive relationship between average annual rainfall and environmental variables such as water availability for plants, vegetation cover, productivity, species diversity, soil properties, human activity, and erosion rates for sub-humid to arid areas (Issar and Bruins 1983; Shmida 1985; Seely 1991; Lavee et al. 1991; Kutiel et al. 2000; Meron et al. 2004). This approach is certainly correct at the global scale, as well as for non-irrigated annual crops in dry-land areas. It is, however, questionable for arid and semi-arid areas, usually regarded as highly sensitive to climate change, especially for perennial plants.