Temporal and spatial changes of rainfall and streamflow in the Upper Tekeze–Atbara River Basin, Ethiopia

Abstract. The Upper Tekeze–Atbara river basin–part of the Nile basin, is characterized by high temporal and spatial variability of rainfall and streamflow. In spite of its importance for sustainable water use and food security, the changing patterns of streamflow and its association with climate change is not well understood in the basin. This study aims at improving the understanding of the linkages between rainfall and streamflow trends and identifying the drivers of streamflow variabilities in the basin. Trend and change point detections of rainfall and streamflow were analysed using Mann–Kendall and Pettitt tests, respectively, using data records for 21 rainfall and 9 streamflow stations. The nature of changes and linkages between rainfall and streamflow were carefully examined for monthly, seasonal, annual flows as well as Indicators of Hydrological Alterations (IHA). The trend and change point analyses found that 20 of the tested 21 rainfall stations did not show statistically significant changes. In contrast, trend analyses on the streamflow showed a significant increasing/decreasing patterns. A decreasing trend in the dry (October to February), short (March to May), main rainy seasons (June to September) and annual totals is dominant in 6 out of the 9 stations. Only one out of nine gauging stations experienced increasing flow significantly in the dry and short rainy seasons. This increasing trend is attributed to the construction of Tekeze hydropower dam above the station in 2009. Overall, streamflow trends and change point timings were found to be inconsistent among the stations. Changes in streamflow without significant change in rainfall suggests other factors than rainfall to drive the change. Weak linkages between rainfall and streamflow trends indicate that the observed changes in streamflow regimes could be due to changes in catchment characteristics of the basin. Further studies are needed to verify and quantify the hydrological changes shown in statistical tests by identifying the physical mechanisms behind those changes. The findings from this study are useful as a pre-requisite for studying the effects of catchment management dynamics on the hydrological variabilities in the basin.