Nonlinearity of ecogeomorphic processes along Mediterranean-arid transect

The study was conducted along a climatic transect extending from the Judaean mountains (mean annual rainfall, 700 mm; annual mean temperature, 17 °C) to the Dead Sea (mean annual rainfall, <100 mm; annual mean temperature, 23 °C).A high correlation was found between climatic conditions and factors and processes of the ecogeomorphological system. The values of certain factors and processes, such as soluble salt content and overland flow, increase with increasing aridity, whereas those of others, such as soil organic matter content, clay content, aggregate size and stability and infiltration rate, diminish with increasing aridity. These trends express the long-term effect of the prevailing mean climatic conditions in the research stations, conditions that led to the development of various types of soil and of plant communities.It was also found that for many of the factors and processes examined, such as organic matter content, salt concentration, aggregate stability, infiltration rate and overland flow yield, the rates of change with respect to position along the transect are not linear, and that a climatic threshold value exists in the zone with a mean annual rainfall of about 300 mm and in which the P/T ratio is about 17, which creates a sharp boundary between arid and Mediterranean ecogeomorphological systems. While in arid systems, erosion occurs mainly through physical–mechanical processes, under Mediterranean systems, it is governed mainly by chemical and biological processes.The significance of the existence of a sharp boundary between the arid and the Mediterranean zones is that even a relatively slight increase in the annual mean temperature and/or a slight decrease in the mean annual rainfall is liable to shift the boundary towards the Mediterranean zone and accelerate desertification processes.