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The Land of Israel is situated on both sides of the 200 mm isohyet, which forms the border between the settled land, to the North, and the Negev desert, to the South. This border shifts annually some 20-50 kms northward and southward in accordance with the rainfall changes. This shifting has a strong impact on rain-grown, traditional agriculture. Long term climatic changes move that border far beyond the annual shifts, extending the desert at add stages. The population size in the Negev increased only during very wet stages and vanished during the arid ones. Looking into the future,regions located at the desert margins should be aware of climatic changes, as Mankind can do very little about the astronomical factors controlling the Earth climate.