Desertification is a pressing environmental challenge with profound ecological and socio-economic impacts, particularly in arid and semi-arid regions such as the southeastern oases of Morocco. Suggestion: This study addresses the critical knowledge gap in the lesser studied but highly vulnerable Rheris watershed by applying the Mediterranean Desertification and Land Use (MEDALUS) approach to assess desertification susceptibility using environmental quality indicators. Climate Quality Index (CQI), Soil Quality Index (SQI), Vegetation Quality Index (VQI), and Management Quality Index (MQI). These indices were integrated to derive a desertification sensitivity index in the Rheris watershed, enabling the mapping and statistical assessment of land vulnerability to degradation. The outcomes showed that 66.85% of the Rheris watershed was critical to desertification, 31.24% fragile, 1.90% potentially sensitive, and only 0.01% low sensitivity. The novel methodological approach of this study in applying MEDALUS to the Rheris watershed provides a comprehensive understanding of desertification dynamics in a region that has received limited attention. The expansion of desertification-prone regions results from the intensified aridity highlighted by the climate quality index, geographic location, and poorly managed human activities, all of which exacerbate the desertification process. The assessment of desertification sensitivity identifies vulnerable areas and anticipates sand encroachment risks. It also offers crucial insights for decision-making and planning and aligns global efforts to achieve the interconnected Sustainable Development Goals (SDGs). The MEDALUS approach is highly adaptable, allowing for selecting and weighing environmental factors like climate, vegetation, soil, and human activities based on local conditions. This flexibility makes it suitable for diverse environments, including Mediterranean, semi-arid, and desertification-prone regions.Graphical AbstractThe graphical abstract illustrates the main criteria used in the MEDALUS approach to analyze desertification in the Rheris watershed (Southeastern part of Morocco), considering four key indices: the climate index, soil index, vegetation index, and management index. The climate index assesses precipitation, exposure, and aridity, while the soil index is based on parameters such as texture, erodibility, depth, and slope. The vegetation index measures plant cover, as well as risks related to fire, drought, and erosion protection. The management index examines human practices, including intensive agriculture and overgrazing. The illustration highlights the methodology used to identify these indices and establish a classification of areas susceptible to desertification. A final map shows the spatial distribution of risk zones, classified according to their vulnerability level (low, moderate, high, very critical), and validated through field visits. Lastly, the graphical abstract emphasizes the main results and stresses the importance of sustainable resource management to mitigate land degradation and protect the environment from climate change and anthropogenic pressures.