Aaron Yair, Speaker at Climate Change Conference
Hebrew University in Jerusalem, Israel
Title : Contrasting eco-geomorphological responses to climatic changes, during the Upper Pleistocene and Holocene periods, in the South Eastern Mediterranean area

Abstract:

Dryland areas are regarded as highly sensitive to climatic changes. A positive relationship between rainfall and environmental factors is often assumed (water availability, species diversity, etc.) for areas with an average annual rainfall of 100-300 mm. This assumption disregards the fact that a climate change in arid areas is not limited to climatic factors. It is often accompanied by a pronounced variability in surface characteristics. Needless to say, the spatial variability of surface properties may have variable effects on water resources and related environmental variables. The present work deals with the complex relationships among the average annual rainfall, surface properties and the spatial redistribution of water resources in a sandy area located in the Northern Negev Desert Two case studies are considered, The first deals with the hydrological effects of biological topsoil crusts on the water regime, along a rainfall gradient (90-180 mm). This study is based on five monitoring sites where the following data have been considered (rainfall, runoff, soil moisture, surface properties, characteristics of the biological elements, and survival of the perennial shrubs along the rainfall gradient. Data obtained show a decrease in water availability with increasing annual rainfall. The findings are attributed to the decisive role played by the non-uniform properties of the topsoil crust along the rainfall gradient. The second study deals with the negative environmental effects of loess penetration into a semi-arid area, during a wet climatic phase. The loess deposit increased infiltration. However, due to the fact that about 80% of the rain-showers are characterized by a low rain intensity (below 5mm/hr1) the depth of rainwater penetration is limited, leading to a soil salinization process during a wet climatic phase. The opposite effect happened during the dry climatic phase. Sand deposition improved rainwater infiltration, allowing the development of a vegetation cover.

Understanding the spatial variability of soil moisture in drylands areas is the key for the agricultural management of loess or sand covered area. For example: sandy areas were often regarded as improper for agriculture. However, today with the drip irrigation system, they are regarded as excellent soils. The y do not absorb water, allowing to provide exactly the water needs of the different plants. On the other hand, the loess saline soils are using for growing the Salicornia plants. A vegetal salt.

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