Assessment of sensitivity to desertification in the Oum Er-Rbia watershed (upstream of Ouled Sidi Driss) using the MEDALUS approach

Abstract

The issue of desertification is a pressing concern for many vulnerable regions, with consequences that extend far beyond their borders. It is a silent force that not only contributes to global climate change by releasing stored carbon from vegetation and soil but also compounds the ongoing environmental challenges we face on a global scale. In Morocco, the effects of these climate changes are already noticeable, particularly in terms of water scarcity due to reduced rainfall and rising temperatures. This, in turn, leads to soil drying and an increased risk of degradation. The Oum Er-Rbia watershed (upstream of Ouled Sidi Driss) is one of the basins affected by this issue, covering an area of 11,152 km² and spanning three topographic units (the Middle Atlas Mountains, the Phosphate Plateau and the Tadla Plain). This topographic diversity causes regional variation in the sensitivity to desertification. Therefore, this study aims to evaluate the sensitivity to desertification in this watershed by using the MEDALUS model (Mediterranean desertification and land use), which calculates the Desertification Sensitivity Index (DSI) through the composition of four indices: the Soil Quality Index (SQI), the Vegetation Quality Index (VQI), the Climate Quality Index (CQI) and the Land Use Quality Index (LUQI). The results show that the critical and highly sensitive zones represent 44% and are located at the northeast and west ends of the watershed. By contrast, the unaffected zones represent 12% of the total area of the watershed and correspond to the upstream area, where the climate, vegetation and land use systems are of good quality, providing effective protection for the land. To reduce the impact of this phenomenon, we have proposed some potentially impactful development actions based on land use and the results obtained.