Mapping soil vulnerability based on the soil erodibility factor (K) in the El Harrar Watershed (Eastern Pre-Rif, Morocco)

Water erosion is a major cause of soil degradation, threatening soil sustainability and agricultural productivity, particularly in environmentally fragile regions. Its intensity is influenced by the interaction of natural and anthropogenic factors, including soil properties, topography, vegetation cover, climate variability, and land-use practices. This study aimed to assess the spatial variability of soil vulnerability to water erosion in the El Harrar watershed (Eastern Pre-Rif, Morocco) using the soil erodibility factor (K), by integrating soil physicochemical characteristics, GIS-based mapping, statistical analysis, and field observations. Previously established K-factor values were assigned to the mapped soil units according to soil-type correspondence to characterize the spatial distribution of soil erodibility across the watershed. The results indicate that 45.15% of the watershed is characterized by low soil erodibility (K < 0.25), mainly corresponding to calcimagnesic soils, whereas 23.78% exhibits very high erodibility (K > 0.45), primarily associated with Fersiallitic soils. Exploratory correlation analysis revealed negative relationships between soil erodibility and organic matter (R = −0.70) and clay content (R = −0.43), suggesting that higher contents of these soil properties are associated with greater soil structural stability and reduced erodibility. These findings highlight the importance of considering soil physicochemical characteristics in assessing the spatial variability of soil vulnerability to water erosion and provide a useful basis for identifying priority areas for soil conservation, sustainable land management, and territorial planning in the Eastern Pre-Rif of Morocco.