Soil erosion risk assessment in Uganda

Abstract

Land use without adequate soil erosion control measures is continuously increasing the risk of soil erosion by water mainly in developing tropical countries. These countries are prone to environmental disturbance due to high population growth and high rainfall intensity. The aim of this study is to assess the state of soil erosion by water in Uganda at national and district levels, for various land cover and land use (LCLU) types, in protected areas as well to predict the impact of support practices on soil loss reduction. Predictions obtained using the Revised Universal Soil Loss Equation (RUSLE) model indicated that the mean rate of soil loss risk in Uganda's erosion-prone lands was 3.2 tha-1y-1, resulting in a total annual soil loss of about 62 million tons in 2014. About 39% of the country's erosion-prone lands were comprised of unsustainable mean soil loss rates >1 tha-1y-1. Out of 112 districts in Uganda, 66 districts were found to have unsustainable estimated soil loss rates >1 tha-1y-1. Six districts in Uganda were found to have mean annual soil loss rates of >10 tha-1y-1: Bududa (46.3 tha-1y-1), Kasese (37.5 tha-1y-1), Bundibugyo (28.9 tha-1y-1), Bulambuli (20.9 tha-1y-1), Sironko (14.6 tha-1y-1) and Kotido (12.5 tha-1y-1). Among the LCLU types, the highest soil loss rates of 11 tha-1y-1 and 10.6 tha-1y-1 were found in moderate natural forest and dense natural forest, respectively, mainly due to their locations in highland areas characterized by steep slopes ranging between 16% to 21% and their high rainfall intensity, ranging from 1255 mmy-1 to 1292 mmy-1. Only five protected areas in Uganda were found to have high mean estimated mean soil loss rates >10 tha-1y-1: Rwenzori Mountains (142.94 tha-1y-1), Mount Elgon (33.81 tha-1y-1), Bokora corridor (12.13 tha-1y-1), Matheniko (10.39 tha-1y-1), and Nangolibwel (10.33 tha-1y-1). To manage soil erosion in Uganda's protected areas, there is an urgent need to control wildfires and human-induced disturbances such as timber harvesting and soil compaction from domestic animals. Our study analysis revealed that well-established terraces and strip-cropping could significantly reduce soil loss rates in Uganda's croplands by 80% (from 1.5 tha-1y-1 to 0.3 tha-1y-1) and by 47% (from 1.5 tha-1y-1 to 0.8 tha-1y-1), respectively, well below the sustainable soil erosion tolerance rate (1 tha-1y-1) for land and water conservation.