Evolution of the Nile River drought risk based on the streamflow record at Aswan station, Egypt

Abstract

The drought in Ethiopian Highlands, source of the Nile flood, has been in the news off and on since the early 1970s, to such an extent that it can be inquired if the Nile basin users are exposed to a drought risk increasing in time. Based on a methodology developed by the author and previously used for flood risk assessment, this article aims to study the progressive modification of the likelihood of occurrence of a certain drought event in the Nile River, based on the annual record available at the Aswan station, Egypt. The record is thoroughly studied to detect possible trends and seasonalities. It is then divided into subsamples, on which frequency analyses were performed using the linear moments (L-moments) method. L-moments perform well with short records and are less sensitive to extremes. The 10-, 25-, 50- and 100-year droughts are estimated based on every subsample, then the temporal evolutions of these estimates are investigated. The results show a cyclic pattern of the drought risk, confirming the previously suggested non-stationarity of the flow series as one of the possible interpretation of the Hurst phenomenon.