Impact of climate change on eco-geomorphic systems and desertification

The impact of climatic conditions on eco-geomorphic processes was studied at a number of research stations along the climatic transect extends between the Judean Mountains (mean annual rainfall 700 mm, temp. 17°C) and the Dead Sea (mean annual rainfall 100 mm, temp. 23°C). The research stations are located on hillslopes having similar gradients, aspects, and lithology.

At each station, climatic and soil variables (rainfall depth and intensity, temperature, soil moisture at different depths), as well as overland flow yield from runoff plots of different lengths (7 m, 14 m, 21 m), were measured. Typical infiltration curves were obtained in field experiments, and soil samples were taken to the laboratory to determine the relevant soil properties (aggregates stability, organic matter content, etc.).

The results show that:

• On a regional scale, there is a correlation between the average climatic conditions and eco-geomorphic processes and variables: the organic matter content, the aggregates size and stability, and the infiltration rate decrease from the Mediterranean to the arid region while the runoff coefficient increases. However, the rate of change of these variables along the climatic transect is non-linear; A step-like threshold exists at the semi-arid region which sharply separates the Mediterranean eco-geomorphic system from the arid one. Such a threshold means that even a relatively small climate change will cause a spatial displacement of the aridity boundary. As many regions having Mediterranean climate are located adjacent to semi-arid regions, they are at risk of desertification even in the case of a slight climate change.
• On the hillslope scale, different spatial patterns of soil properties values and of overland flow generating areas characterize different sections of the climatic transect. In the Mediterranean and the arid regions the spatial distribution of soil properties values is uniform but the values themselves are very different. While in the Mediterranean region the values promote infiltration, in the arid region they promote overland flow generation. In addition, the vegetation cover in the Mediterranean region is almost 100% while in the Arid zone it is close to 0%. The result is that in the Mediterranean region infiltration is the dominant process all over the hillslope while in the arid region overland flow predominates. In contrast to the uniform spatial distribution of processes in these two regions, the semi-arid region is dominated by a mosaic-like spatial pattern, consisting of locally “dry” water source patches and “moist” water sink patches. These patterns express different adaptation/survival strategies of eco-geomorphic systems under different climatic conditions.

Changes in the spatial patterns of soil properties values and of vegetation together with a change in the ratio source/sink areas can be used as quick response indicators of climate change and of desertification.

Regarding rehabilitation strategies, triggering the regeneration of a mosaic soil-vegetation pattern in the semiarid region should be preferred as a more sustainable option than treating areas as homogeneous landscape units.