Abstract
The Nile is the longest river in Africa stretching over around 6650 km through 11 countries. From the times of the ancient Egyptian Pharaonic civilization, the Nile is known to be a blessing, which provides major resources including water and fertile soil for agriculture, and facilitates transportations and international trades in nearby countries. Due to its invaluable importance to local economy and agriculture, it is undoubtedly of paramount importance to know how the variability of the Nile is controlled by local and global climate and its morphological characteristics. Here, we utilize a newly developed time-series analysis method applied to monthly Nile river inflow data to reveal various factors changing the river inflow from seasonal to inter-annual, decadal and beyond. On seasonal time-scales a positive feedback, associated mostly with river’s morphological change driven by summer precipitation, is identified as a main mechanism for maximal variability in September leading to major flooding or drought. In particular, the positive feedback is quite similar in its mechanism to major climate feedbacks observed, e.g. with ice albedo and Bjerknes feedbacks. The slow time-evolution of the positive feedback explains human endeavour history to control nature, such as the control of the Nile annual flooding through dam construction. The analysis of climate association reveals clear link with large-scale and low-frequency forcing. Decadal and multi-decadal timescales of local precipitation and associated teleconnection with atmospheric and oceanic circulation can be traced back to the Pacific Ocean, and involve mostly the El-Nino Southern Oscillation and the Pacific Decadal Oscillation.
Acknowledgements
We thank J. S. Wettlaufer for discussion of this study and helpful feedback. WM acknowledges the support of Swedish Research Council grant no. 638-2013-9243. Two anonymous reviewers provided constructive comments that helped improve the manuscript. We thank Prof. H. A. Basset for sharing the Nile discharge time series.
Disclosure statement
No potential conflict of interest was reported by the authors.