Impact of land cover and soil conservation on soil erosion rates in the Tikur Woha Catchment, Ethiopia

Abstract

In Ethiopia both the population and economy are growing rapidly, which results in land cover changes. Over the last decades natural vegetation like forest is replaced by cultivated land and settlements and new cash crops are introduced in parts of Ethiopia. As a result, soil erosion increased in many part of Ethiopia. To assess the effect of land cover change on soil erosion five different land cover and soil conservation scenarios are constructed for a case study in the Tikur Woha catchment. One scenario represents a natural reference scenario, two scenarios represent the increase in cash crops (khat and sugarcane), one scenario is based on current policy that replaces khat on steep slope by forest, and the last scenario represents the current land cover when soil and water conservation is applied. Furthermore, an assessment of the current soil erosion is made. In this study the Soil and Water Assessment Tool is used to quantify the erosion rates of the different scenarios. Better understating of current and possible future erosion rates and their spatial distribution will be of great value in reducing future soil erosion and maintaining food production.

Results show an average soil erosion rate of 4.32 t h-1 y-1 for the Tikur Woha catchment over the modelled period of 2005-2010 with current land cover. Only 5% of the catchment is exposed to erosion rates above 15 t h-1 y-1. The lowest erosion rates are found for the reference scenario with an average soil erosion rate of 0.12 t h-1 y-1. When the reference scenario is excluded, the soil conservation scenario results in the lowest average erosion rate (3.26 t h-1 y-1), and is the most effective in reducing soil erosion in most the sub basins. The policy scenario is less effective in reducing average soil erosion rates (4.00 t h-1 y-1). The two cash crops scenarios show a negative (4.68 t h-1 y-1) and a small positive effect (3.46 t h-1 y-1) on soil erosion rates. If the current land cover trend continues and both natural land cover and agricultural land cover are replaced, soil erosion rates will increase. Therefore, policy should focus on implementing soil conservation and restoring and maintaining natural vegetation to reduce soil erosion rates in the Tikur Woha catchment.