Intra-Annual Variation of High and Low-Flow Extremes Associated With Land Use and Climate Change in the Upper Tekeze of the Nile River Basin

In northern Ethiopian highlands, climate variability and land use/land cover (LULC) change has been observed during the past decades. However, it remains unclear that to which extent and how these key drivers contributed to changes in hydrological extremes. As a case study, the respective impacts of LULC change and climate variability on hydrological extremes with respect to magnitude, duration, and frequency metrics were assessed in the Upper Tekeze basin, Ethiopia. A scenario-based approach using LULC and hydro-climatological data was developed and five simulation experiments were conducted using Soil and Water Assessment Tool model. Results showed that, during 1986-2015, low-flow duration has decreased by 5.0 days/yr, and the magnitude and occurrence of high flow has increased by 5.23 m(3)/s/yr and 5.11 days/yr, respectively. Meanwhile, about 47.42% of the landscape has changed its category while no significant change was detected in annual rainfall during the past 31 yr. Particularly, rocky area increased by 82% which was mostly contributed by losses of bare, sand, and low biomass areas. Significant positive and negative contributions to the changes in high and low-flow extremes, respectively, were detected from LULC change, while no significant contribution was detected from climate change. The increased rock area tends to be one of the major contributors to the increased high flow while climate change seemed to play a minor role. The potential mechanism is the expansion in rock area increased runoff and high flow, which may lead to significant land deterioration and loss of water storage capacity in the mountainous basin.

Automated summary

Climate variability and land use/land cover change in the northern Ethiopian highlands have been observed to contribute to changes in hydrological extremes. Results show that land use/land cover change has a significant impact on high and low-flow extremes, while climate change has a minor role. The increase in rock area is a major contributor to increased high flow.