Land surface climatology and land cover change monitoring since 1973 over a north‐Sahelian zone (Ansongo ‐ Mali) using landsat data

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Abstract
The study, based on Landsat 1, 2 and 5 data, outlines the changes that have occurred in the north‐sahelian sector of Ansongo, in the north‐east of Mali. The images were corrected for radiometric and atmospheric effects and used for calculating the surface albedo and the vegetation index following the normalized difference method (NDVI). The analysis of the variations of these two parameters is suggestive of a continuous and significant trend towards desertification in the southern part of the study area between 1973 and 1986, with a 15% increase in the albedo and a 17% decrease of the NDVI. In the northern area, the trend is less pronounced with an 8% increase in the albedo. A classification of the land cover into eight classes for each date helps explain the degradation processes involved. The results show an important anthropic pressure on the vegetation cover. This analysis thus highlights the important spatial variability of land surface temporal evolution in the Sahel, which must be taken into account in a mesoscale regionalization study.