Recent trends and fluctuations of rainfall in the Upper Blue Nile River Basin

Abstract

During the last decades, water resource managers are facing severe challenges all over the world, and the trends of temperature and precipitation intensify this situation. Knowledge of the spatial variability and temporal trends of rainfall is essential for efficient management of water resource and agriculture. Rainfall plays a crucial role in the process because its variations, coupled with changes in extreme events, can influence water resources, on natural environments and human activities, as well as on human health and safety. In this chapter, an investigation of the rainfall variability of the Upper Blue Nile River Basin, the main source of the Nile River, was carried out by means of a daily rainfall data set of 22 meteorological stations with 48 years of observation. The nonparametric Mann–Kendall test and the Sen’s slope estimator were used to identify the existence of trends and slope magnitude in rainfall at seasonal and annual scale. Results revealed that although there was a mix of positive and negative trends, they were statistically insignificant except at one station. In contrast, the trend and change point analyses of annual series found that 21 of the tested 22 rainfall stations did not show statistically significant changes. Furthermore, analyses of rainy seasonal series (June–September) showed significant changes only at 1 out of 22 stations. The spatial analysis of the trend in the Upper Blue Nile River Basin for several time scales showed that the negative trends are in western side and the positive trends are on the eastern side of the basin.