Impact of deforestation on soil erosion in the highland areas of western Ethiopia using geospatial techniques: a case study of the Upper Anger watershed

Soil erosion is a major environmental problem in developing countries mainly due to forest cover loss driven by agricultural expansion. The current study aimed to analyze the impact of vegetation cover loss from elevated areas on soil erosion in the Upper Anger watershed using geospatial techniques and the revised universal soil loss equation (RUSLE) model. The mean annual soil loss in the study area was calculated using five factors: rainfall, soil type, slope length and steepness, cover management, and conservation practices. Furthermore, the normalized difference vegetation index and slope were used to calculate the relationship as well as the cause and effect of soil loss in the study area. The results revealed that the mean annual soil loss in the Upper Anger watershed was 44 ton/ha/year in 1989, 66.4 ton/ha/year in 2002, and 87.9 ton/ha/year in 2020. The annual soil loss in agricultural land increased from 75.9 ton/ha/year in 1989 to 98.5 ton/ha/year in 2002 and 103.8 ton/ha/year in 2020. The annual soil loss of the Upper Anger watershed increased by 99.8% due to a decline in vegetation cover from elevated areas for agricultural expansion based on adjusted R2, with the remaining percentage possibly increasing due to other factors. Due to deforestation, the area of soil erosion increased from 551.8 km2 (29.5%) in 1989 to 821.6 km2 (44%) and 1043.8 km2 (55.8%) in 2002 and 2020, respectively. This study identifies severe erosion loss areas for mitigation measures. To minimize the severity of soil loss in the study area conservation measures, such as re-afforestation, area closure, agroforestry practices, and participatory watershed management, should be promoted by governmental and nongovernmental organizations.