Multi-Temporal RUSLE Assessment of Soil Loss and its Drivers in the Idah Catchment, Kogi State, Nigeria (2000–2025)

Few West African catchments have the monitoring records needed to track erosion over time. For the Idah Catchment (1,642 km²), Kogi State, Nigeria, annual soil loss was modelled at 30 m resolution for 2000, 2010, 2020 and 2025 with the Revised Universal Soil Loss Equation (RUSLE), and the roles of erosivity and land cover in the change were examined. Erosivity was estimated from the modified Fournier index (2000–2020) and storm EI30 (2025); erodibility from ISRIC SoilGrids; the topographic (LS) term from 30 m SRTM elevation data; cover management from classified Landsat imagery (2025 accuracy 85.09%, κ = 0.82); and support practice from field-observed conservation measures. Mean soil loss fell from 13.29 to 6.87 t ha⁻¹ yr⁻¹ (48%), and high and very high-risk land contracted from 19.6% to 6.7% of the catchment. The decline is not a statistically established trend (p = 0.128, n = 4), and the 2025 value is affected by a change in the erosivity method. Between 2010 and 2020, however, erosivity fell 21.8% while mean soil loss rose 1.2%, the mean cover-management factor rose from 0.115 to 0.128, moderate-risk land expanded by 116.65 km², and soil loss in Ofu Local Government Area rose 31.0% as cropland reached its maximum extent (61.3%). Agricultural expansion therefore cancelled the climatic benefit at catchment scale and reversed it in Ofu. Topography governed the spatial pattern, with the LS term the most variable (coefficient of variation 123.0%). The 2025 surface should be read as a reference point for future monitoring.