Soil erosion risk assessment using RUSLE and geospatial techniques in Peruvamba sub-watershed, Kerala, India

Abstract

Soil erosion is a major environmental challenge in the humid tropical landscapes of the Western Ghats, where intense monsoonal rainfall, steep terrain, and land-use changes accelerate land degradation. This study evaluates soil erosion risk in the Peruvamba sub-watershed of Kerala, India, using the Revised Universal Soil Loss Equation (RUSLE) integrated with Geographic Information System (GIS) techniques. Rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C), and conservation practice (P) factors were derived from multi-year rainfall records (2014–2023), soil survey data, satellite imagery, and digital elevation models. The average rainfall erosivity was estimated at 2710.67 MJ mm ha⁻¹ h⁻¹ yr⁻¹, while the LS-factor reached a maximum value of 28.88 in steep upland areas, indicating a strong topographic influence on erosion processes. The RUSLE-based assessment estimated a total annual soil loss of approximately 72,500 t yr⁻¹ and a mean soil loss of 17.4 t ha⁻¹ yr⁻¹, exceeding the commonly accepted soil-loss tolerance threshold for tropical regions. Forested and wetland areas exhibited low erosion rates, whereas agricultural lands, plantations, and scrub-dominated areas experienced moderate to severe erosion. Approximately 5.3% of the watershed was classified as very high erosion risk, while 14.7% of the area fell within high to very high erosion categories, representing priority zones for conservation intervention. The results demonstrate that topography and vegetation cover are the dominant controls on soil-loss variability and highlight the importance of targeted soil and water conservation measures, including contour bunding, terracing, and vegetation restoration. Comparison with published erosion estimates from comparable Western Ghats watersheds and sensitivity analysis indicated good agreement and supported the reliability of the model outputs. The integration of RUSLE and GIS provides a robust and scalable framework for erosion-risk assessment and supports sustainable watershed management in the Western Ghats and other tropical environments.