Temporal and spatial changes of rainfall and streamflow in the Upper Tekezē–Atbara river basin, Ethiopia

Tesfay G Gebremicael,Pieter V Zaag,Yasir A Mohamed,Eyasu Y Hagos

doi:10.5194/hess-21-2127-2017

Abstract

Abstract. The Upper Tekezē–Atbara river sub-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. This study aims to improve the understanding of the linkages between rainfall and streamflow trends and identify possible drivers of streamflow variabilities in the basin. Trend analyses 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 and annual flows, as well as indicators of hydrologic alteration (IHA). The trend and change-point analyses found that 19 of the tested 21 rainfall stations did not show statistically significant changes. In contrast, trend analyses on the streamflow showed both significant increasing and decreasing patterns. A decreasing trend in the dry season (October to February), short season (March to May), main rainy season (June to September) and annual totals is dominant in six out of the nine stations. Only one out of nine gauging stations experienced significant increasing flow in the dry and short rainy seasons, attributed to the construction of Tekezē hydropower dam upstream this 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 factors other than rainfall drive the change. Most likely 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 prerequisite for studying the effects of catchment management dynamics on the hydrological variabilities in the basin.

Highlights

Recent changes in climatic conditions combined with other anthropogenic factors have increased the concern of the international community for water resources management in basins (Jones et al, 2015; Zhang et al, 2008)
This study presents a detailed statistical analysis on the existence of trends and point changes of rainfall and streamflow in the Upper Tekeze River basin
The result of this study clearly showed that monthly rainfall in the majority of the stations experienced high spatial variability compared to the seasonal and annual timescales

Summary

Introduction

Recent changes in climatic conditions combined with other anthropogenic factors have increased the concern of the international community for water resources management in basins (Jones et al, 2015; Zhang et al, 2008). Kim et al, 2008; Ma et al, 2008; Pano et al, 2010; Tekleab et al, 2013; Wang et al, 2013; Zhan et al, 2014; Zhao et al, 2015). These studies investigate how climate change, reflected in changing rainfall patterns, affects the hydrological regimes of river basins. There are a number of studies (e.g. Tekleab et al, 2013; Gebremicael et al, 2013; Wang et al, 2015; Hannaford, 2015; Saraiva-Okello et al, 2015) who found that changes in rainfall are not sufficient to explain the trends in the streamflow

Objectives

Results

Conclusion