Identification of critical soil erosion prone areas and annual average soil loss in an upland agricultural watershed of Western Ghats, using analytical hierarchy process (AHP) and RUSLE techniques

The present work integrates analytical hierarchy process (AHP) with Revised Universal Soil Loss Equation (RUSLE) model to determine the critical soil erosion prone areas along with the spatial pattern of annual average soil erosion rates of an upland agricultural sub-watershed in the Western Ghats of Kerala, India. The critical soil erosion prone areas were identified by integrating geo-environmental variables such as land use/ land cover, geomorphology, drainage density, drainage frequency, lineament frequency, slope, and relative relief after determining its relative contribution in conditioning the terrain susceptible to soil erosion by AHP technique, in a raster-based Geographic Information Systems environment. The spatial pattern of average annual soil erosion rates was obtained by RUSLE model that consider five factors, viz., rainfall erosivity (R), soil erodability (K), slope length and steepness (LS), cover management (C) and conservation practice (P) factors. The soil erosion probability map prepared by the AHP method was reclassified into soil erosion severity map showing regions of different erosion probability. Among this, the critical erosion zone occupies 4.23 % of the total area followed by high erosion severity zone occupies 18.39 % of the study area. Nil and low zones together constitute 44.15% of the total area. The assessed annual average soil loss from the watershed shows an increased value of 4,227 t(-1) h(-1) year(-1) as the maximum loss. The cross-comparison of potential soil erosion severity map with annual average soil loss in the area validates the finding of the study by a high spatial correlation. More erosion proneness and annual loss were observed in areas where the side slope plateau, denudational slope, and valley fills comes with high slope and relative relief. The intense terrain modification in this area with improper soil conservation measures makes the watershed more vulnerable to soil erosion.