Climate and human activities impact on runoff and sediment yield in the central rift valley of Ethiopia

This study analyzed the effects of climate variability and human activities on runoff and sediment yield of a watershed in the Central Rift Valley of Ethiopia since the 1980s. In the study, innovative trend analysis, the Pettitt test, and sequential regime shift detector methods were used to analyze trends and abrupt changes during the period 1981-2020. The Soil and Water Assessment Tool model was then integrated to disaggregate the contributions of climate variability, land-use change, and direct human activities on runoff and sediment yield at the watershed scale. The result indicates that the runoff and sediment yield decreased significantly with a sudden change in 2001. The study found that direct human activities played a dominant role, accounting for 57.9%, and 53.4% of annual runoff and sediment yield reduction, respectively. On the contrary, changes in climate and land use have led to a slight increase in runoff and sediment yield after 2001. The greater impacts of human activities can be attributed to the growth rate of water abstraction, and riverbed sand excavation during the past four decades. The findings of the result could be useful in supporting decision-makers in achieving watershed sustainability.