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Abstract
This paper examines the long-term historical changes in frequency and amplitude of rainfall extremes in two very close stations of Addis Ababa, the Addis Ababa Observatory (AAO) and Addis Ababa Bole (AAB) records including some surrounding measurements using the second half of 20th century data. The method used to examine trends and oscillatory patterns is the quantile perturbation method, especially designed for extreme conditions. The result shows that the Addis Ababa Observatory (AAO) shows an exceptionally increasing trend in its extreme events while the rest of the stations show an oscillating pattern. Exceptional behaviour at AAO is also noticed from unique global climatic indices. Both Pacific Decadal Oscillation and the Southern Oscillation Index are opposed to other stations. A possible reason for the increasing trend is linked with the growing urbanization that has been occurring in Addis Ababa city in the past decades. Nevertheless the variability of AAO rainfall extremes is within the uncertainty range that indicates natural variability. Although the change may not be severe at present, it is important to note the increasing trend to avoid serious consequences in the future.
Acknowledgements
The authors acknowledge the National Meteorological Agency in Ethiopia for the provision of data. The research was carried out in the framework of the FRIEND/NILE projects of UNESCO and the Flanders in Trust Fund of the Flemish Government of Belgium. Financial support was provided by a DBOF scholarship of KU Leuven. The first author extends acknowledgement to the University of Connecticut for providing me visiting scholarship assistance to which this paper was completed.