Diachronic evolution of wetlands in a desert arid climate of the basin of Ouargla (southeastern Algeria) between 1987 and 2009 by remote sensing

The region of Ouargla is located in the bed of M’ya River (lower Algerian Sahara) that represents the main artery of dry wadis. The superficial water table outcrops in depressions in the form of salty wetlands (Chotts and Sebkhas). These humid zones are influenced by different factors that degrade its environment: natural factor, mainly the anthropic factor, leading to the fluctuation of the static level and to the augmentation of water, and land salinity, which directly influences the oasis ecosystem. The objective of the present study is to follow the evolution of the humid surface state in order to map the changes and to identify the influencing factors. The study is based on the diachronic evolution of wetlands in the region of Ouargla between the years 1987, 2000, and 2009, with the statistical analysis and mapping changes obtained from satellite images Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) Landsat. The results have shown important changes on the occupation of the land in the region where we have observed a progress of vegetation, surfaces of polluted water because of anthropic factors, urban development, inadequate management of drinking water, and water of drainage. The humid land has proved changes of humidity rates which are related on one hand to the water of irrigation that furnishes the superficial water table and, on the other hand, to the climatic factors that cause the evaporation of the underground water that is close to the surface of the land.