Water erosion in Mediterranean watersheds requires an integrated assessment of terrain susceptibility, surface protection and soil-loss patterns to guide conservation planning. This study combines the predictive, descriptive and integrative phases of PAP/CAR with RUSLE in the Oued Aggay watershed, northern Morocco. Lithology-derived material friability and slope define qualitative erodibility, while land use and vegetation density determine soil protection; predictive erosion status is subsequently combined with the erosion-form inventory. RUSLE estimates an annualised fixed-cover scenario using long-term rainfall erosivity, SoilGrids mean properties over 0–15 cm, SRTM-derived terrain, Landsat cover conditions of 24 September 2026 and P = 1. On the common 384.59 km² analytical domain, high to extreme erodibility accounts for 19.94% of the area, weak to very weak soil protection for 45.94%, and high to very high erosion status for 28.55%. Rill erosion is the dominant mapped form (31.41%), while 57.99% of the domain falls within the consolidated diagnostic category of generalised expansion or intensification. With a prescribed 0.1 km² bound on the LS contributing-area term, mean modelled soil loss reaches 26.92 t ha⁻¹ yr⁻¹, corresponding to an integrated total of 1.035 million t yr⁻¹. Severe and very severe classes account for 83.26% of modelled loss across 47.41% of the domain. Alternative finite LS bounds change integrated loss by −2.36% to +6.65% and retain at least 97.70% of reference very severe cells. These complementary results identify priority terrain units for process-specific soil and water conservation, supported by an archived reproducible GIS workflow.