Cartographie de la dégradation des sols par une approche géomatique dans la région d'Azilal, Haut Atlas marocain

Abstract

Changes in land cover at a regional scale and the assessment of the risk of soil degradation at the scale of the basin require not only information on the physical structure of soil but also appropriate tools to evaluate these changes. In order to identify the areas subject to a high risk of degradation in a region of Northern Africa, a geomatics approach integrating the following variables was considered: state of soil degradation, slope length, aspect, presence of vegetation and the erosive potential of overland flow. In order to map the state of soil degradation, the Hue and the Coloration indices were calculated from remotely sensed imagery. The complimentary nature of these two spectral indices allows the identification of the different levels of soil degradation. A vegetation index, MSAVI(2), was used to obtain a map of vegetation. Geomorphometric data (aspect, slope length, stream power index), were derived from a DEM generated in a GIS from a topographic map at a 1:50 000 scale. These data were integrated in a GIS by means of a multicriterion model. Multicriterion evaluations were then performed to identify and map areas of potential degradation. Model results were then compared with a cartographic document (reference map) using the Kappa coefficient. Comparisons between modeled potential degradation and the reference map showed overall low levels of agreement. Subsequently, a visual comparison using photographs of the study area was also performed as a way to further evaluate the results of the proposed method. (Abstract shortened by UMI.)