Evaluation of Spatial Distribution of Soil Loss Using the RUSLE Model for the Akanyaru Sub-Catchment of Rwanda

Soil erosion is a major environmental problem driven by land use change and unsustainable agricultural practices, particularly in Rwanda, where half of agricultural land is moderately to severely degraded. This study assessed soil loss in the Akanyaru Sub-catchment using the Revised Universal Soil Loss Equation (RUSLE) integrated with GIS and validated with field measurements from 876 rainfall events recorded on 12 runoff plots representing four land-use types. The model incorporated rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C) for 2024 and 2025, and a constant conservation practice (P) factor. R values ranged from 1100 to 2400 MJ mm ha−1 h−1 yr−1, K from 0.20 to 0.35 t h MJ−1 mm−1, LS from 0 to 256, and C from 0.01 to 0.99. Estimated annual soil loss ranged from 0 to 650 t ha−1 yr−1. From 2024 to 2025, mean and median soil erosion rates decreased by 5.21 and 18.7 t ha−1 yr−1, respectively, and total annual soil loss declined by 812,654 t (11.45%). Model validation showed strong agreement with field observations (R2 = 0.97, NSE = 0.95, nRMSE = 26.32%, PBIAS = −12.47%), demonstrating the reliability of the RUSLE–GIS approach for soil erosion assessment and conservation planning.