Etudes des dynamiques spatiales d’évolution de l’occupation et de l’utilisation des sols dans la fenêtre lacustre camerounaise du lac Tchad et son arrière-pays à partir des grandes sécheresses sahéliennes de 1970.

Résumé

The environmental context in the Sahelian region, from the 1970s is marked by the Sahelian great droughts which followed the wet periods of the 1950-1970 decades, and preceded the return of humidity observed at the beginning of the 2000s. These environmental changes have brought out important modifications in the ecosystems and their uses. The aim of this doctoral thesis is therefore to study, from a multi-scale, multi-sensor and multi-temporal analysis of land use and land cover, the consequences of these environmental changes on the Sahelian ecosystems, through the Cameroonian shores of Lake Chad and its hinterland. The MODIS MOD13Q1 time series images available from 2000 are then used to map the main vegetation classes, analyze the state of the vegetation cover and determine its spatial and temporal evolution trends. The Landsat, Sentinel 2 and SPOT 6 images available since 1972 (for Landsat), are used for a diachronic study of land use and land cover changes of the study area according to Sahelian climatic and environmental changes, with the aim of to identify and highlight the effects of these changes on the use of naturals resources. The results shows that after the aridification of land cover during the great droughts, a dynamic of re-greening of the study area takes hold from the 2000s, through the annual vegetation cover which gradually grows on the bare soils. The re-greening observed increases the availability of the pastures, and improves the accentuation of anthropic pressures on the natural’s resources by the increase of agricultural areas and built-up surfaces. The modeling of the land use and land cover according to the geographical factors of changes and according to the morphological structure and the functional characteristics of the elements of surface, shows then that it is possible to determine large territorial units present in the study area.

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