Gully Erosion Risk Assessment Using Multi-Criteria Analysis: A Case Study of the Oued Rhéraya Watershed

Morocco's climate is predominantly semi-arid and arid, with 93% of its territory falling under these classifications. Land degradation poses a significant environmental risk, particularly in the mountainous regions of the High Atlas. These areas are marginalized in development and economic growth, with an average soil loss of 35 t. ha־ˡ. yr־ˡ according to REEM, 2015.The severity of this phenomenon is expected to escalate due to the interplay of natural and anthropogenic factors, often exacerbated by unsustainable resource management and exploitation practices. Among the various forms of water-induced soil erosion, gully erosion is the most dynamic and destructive, adversely affecting the land and the livelihoods of local populations in mountainous regions, such as the Rhéraya watershed in the Western High Atlas. Mitigating this degradation process and addressing its impacts are critical for reducing local vulnerabilities and enhancing the resilience of socio-ecological systems. Effective risk reduction necessitates the adoption of decision-making tools tailored to specific territories, enabling comprehensive diagnostics and prioritization of intervention areas based on severity. This study aims to systematically classify gully erosion risk within the Rhéraya watershed using an ordinal scale. The risk assessment integrates two components: hazard and vulnerability, evaluated through indicators aggregated via multi-criteria analysis (MCA). These indicators encompass biophysical factors (e.g., land use, slope inclination and length, rock friability, and soil type) and social dimensions (e.g., human, infrastructural, and economic stakes associated with soil degradation). The methodology draws inspiration from the SCALES model (Spatialisation d'éChelle fine de l'ALéa d'Erosion des Sols), the Analytic Hierarchy Process (AHP), and spatial modelling techniques using Geographic Information Systems (GIS). The developed model serves as a strategic tool for soil conservation and restoration efforts, protecting environmental goods and services while bolstering the resilience of local communities. Key outcomes include a systematic territorial classification highlighting gully erosion risk and its implications for both environmental and socio-economic assets. The main objective of this study is to assess the vulnerability to soil erosion in the Riraya basin by implementing a multi-criteria methodology for evaluating erosion risks, taking into account the characteristics of erosion risk and vulnerability in order to create a comprehensive system for diagnosing and monitoring the state of erosion in the watershed, which makes it possible to identify the areas at risk that need to be protected as a priority. In light of the results obtained, the risk of gully erosion appears to be active and significant across more than half of the watershed (51.20% of the area, or 11,531 ha), with fairly high hazard and vulnerability rates. The accuracy rate was estimated at approximately 86.67%, which guarantees the reliability of the results obtained and the validity of this model in estimating erosion risk.