An oasis means, in the common language, a vegetated area isolated in the middle of a desert or semi-desert area. But first of all, it is mainly a man-made territory created around a water management system: close to a spring, or where the water table is close enough beneath the ground, or sometimes in the bed of a wadi that leads into the desert.
Since the 1940’s, new oases have been created through drill irrigation, sometimes following oil drilling. They are areas cultivated thanks to irrigation, and characterized by the association of a human settlement and a cultivated area (often a palm-tree grove) in a desertic or semi-desertic area.
As a hydrosystem (often an underground one), oases are considered by Ramsar as a special wetland type. Whether it is through irrigation by a seguia system, by pumping underground water, or by the antique foggara system, these wetlands are characterized by canals (incl. seguias), storing reservoirs, marshes created by water leaking from the canals, and by irrigated fields (palm-trees and vegetable gardens).
Traditional cultivated oases are often rich in biodiversity and provide drinking water to resident and migratory animal populations, that would otherwise not be able to survive in the desert. Recent palm-tree plantations – as cash-crops - often rely on pumped water, machinery and fertilizers, and are less favourable to the fauna and flora.
Saharan oases, both man-made and natural, only cover one-thousandth of the Sahara surface.
Oases have always played an important role in the development of trade roads used by caravans, that used to find in them water and food. Today they are the target of development projects for their agriculture and tourism potential. Their survival depends on the wise use of water. Some of them will continue to exist so long as access to the water is maintained, whereas others continue to vanish when water has been over-exploited.
A few examples of oases :
