Decadal Trends of Soil Loss and Runoff in the Koga Catchment, Northwestern Ethiopia

Abstract

This study used the physically based distributed Annualized Agricultural Non‐Point Source model to simulate decadal trends in soil loss and runoff with changes in land use/cover in the 98·4 km2 upper part of the Koga catchment. The study indicated that soil loss in the study area has increased from 17 Mg ha−1 y−1 in 1957 to 25 Mg ha−1 y−1 in 2010 because of a decrease in the amount of woody vegetation cover. We found that over the past 50 years, high risk erosion areas with soil loss greater than 35 Mg ha−1 y−1 covered, on average, 41% of the study area, while these same areas contributed, on average, 78% of the soil loss from the study area. Twenty one percent of the study area has been in the high risk erosion category throughout all the years since 1957. The total amount of soil loss from the study area varied with changes in the amount of woody vegetation cover. Other factors such as landforms and soil type also affected the amount of soil erosion. Whereas most of the high erosion areas were found in the upper part of the catchment, most of the high runoff areas were found in the lower part of the catchment, indicating that the amount of soil erosion is not directly related to runoff volume in the study area. Crop fields contributed to most of the soil loss in the study area. Copyright © 2015 John Wiley & Sons, Ltd.

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