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Geological evolution inducing natural desertification in the arid zone of the Middle East – past, present and future

Geological evolution inducing natural desertification in the arid zone of the Middle East – past, present and future

Yoav Avni
Geological Survey of Israel

In the arid zone of the Middle East, dynamic relations between precipitation, runoff, soil development and soil erosion are inducing water availability and natural biomass. These dynamic relations are dictated by the glacial – inter glacial oscillations, supper-imposed on a general trend of permanent aridity observed during the last 2 Ma. Present manifestations of this process is the widespread phenomenon of naturally induced soil erosion, initiated 20,000 years BP at the transition from the last glacial phase to the present interglacial phase and intensified during the Holocene.

The aggressive process of soil erosion gradually removes the loessic soils that developed during the last glacial event, holding agriculture potential. Simultaneously, as the bedrock exposed, this process contributes to runoff generation and water availability. As this process is self-accelerated, the rate of soil erosion is gradually increasing.

Pastoral and agricultural societies living on these lands throughout the Holocene has intensified or slowed down the natural process of soil erosion. Intensified grazing can cause accelerated soil erosion and desertification while construction of agriculture installations such as terraces can contribute to soil conservation. In this regard, the remains of the farming society that lived in the Negev Highland of Southern Israel during the Byzantine and Early Muslim eras (1700-1100 BP) are giving insights on large-scale and long-term actions of soil protection. During this period, most of the valleys were terraced and leveled, aiming to protect agriculture soils and to slow-down the flood energy, permitting flood water to percolate into the soil. Hundreds of cisterns were dug, offering drinking water for humans and herds. The crops in the agricultural plots were mainly cereals – barley and wheat, while orchards of olive and grapes were planted in deep irrigated soils. Plantation of similar orchards at present, solely irrigated by runoff, prove that the ancient agricultural enterprises were constructed under similar arid climate, limited to 130-70 mm/y. All environmental indicators in the region hints on the stability of the present climate for the last 3000 years.

At present, agriculture potential is still kept in the majority of this arid zone. However, positive feedback mechanism is speeding-up soil erosion, promoting desertification. As a globe-wide warning was set for combating desertification, the effect of increased water availability combined with new agriculture techniques, reinforced by solar energy, are giving hope for better land management that will slow down the natural desertification process in arid zones glob-wide.