Integrating USLE, GIS, and AHP for soil erosion assessment and mitigation prioritization in Samosir Island, Indonesia

Abstract

Soil erosion has become one of the most severe forms of land degradation in tropical mountain areas due to the combined effect of steep topography, high rainfall erosivity, and rapid land-use change. The island of Samosir in the Lake Toba catchment has experienced increasing pressure from agricultural expansion and forest conversion. The study aimed to assess the spatial distribution of soil erosion hazard and to identify mitigation priorities by employing an integrated GIS-USLE-AHP framework on Samosir Island. Soil erosion was estimated using the Universal Soil Loss Equation (USLE) by integrating rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), and cover-management (CP) factors in a Geographic Information System (GIS) environment. Rainfall erosivity was computed from CHIRPS precipitation data (2010-2025), topography was extracted from DEMNAS, and land cover was classified from Sentinel-2 imagery using the Random Forest algorithm in Google Earth Engine. The Analytical Hierarchy Process (AHP) was used to identify mitigation priorities. The results showed that very low erosion hazard dominated the island with 28,481.03 ha (44.01%). The AHP analysis revealed that the highest-priority strategy was vegetative mitigation (0.503), followed by human resource strengthening (0.319) and mechanical conservation measures (0.177), with a highly acceptable consistency ratio (CR = 0.00158). Agroforestry, revegetation of critical slopes, and conservation-based community empowerment were the best mitigation measures.