Soil Erosion Mapping Using the PAP/RAC Directive and Spectral Indices

The present work aims to study the water erosion in the watershed of Oued Rmel located in the North-East of Tunisia, using the PAP/CAR approach and the Geographic Information Systems (GIS). This method is focused on the integration of factors influencing water erosion (slope, vegetation cover and lithology) and then the search for the relationship that can link the result of the used methodology with the three spectral indices (NDVI, IB and MSAVI) that are most used to analyze the state of soil degradation. The modeling presented by the PAP/RAC guidelines was able to determine the changes in soil erosion risk between 2000 and 2020, and to identify priority areas for intervention. In fact, an area of 58 km2 presented an aggravation of erosion during the studied period. The analysis of the erosive map conditions in the year 2020 shows that only 13.9% of the studied area represents a very low erosive condition. This class is largely located in forested areas. However, the watershed is dominated by a low to medium erosive state, 68%, located in the central plain whose NDVI fluctuated between 0.25 and 0.5, the MSAVI between 0 and 0.4 and a gloss index that varies between 5 and 25%. The very high erosive class is also found in the northern and southwestern areas and does not exceed 5%. These areas are still undeveloped and require urgent intervention mainly on bare soils translated by a percentage of 45% of IB, or by the implementation of soil conservation techniques.