Decadal periodicities of Nile River historical discharge (A.D. 622–1470) and climatic implications

The Roda Milometer (Cairo, Egypt) has recorded more than 2,000 gauge readings, i.e. annual low‐water and flood levels, from A.D. 622 to the beginning of this century. Spectral analysis of the A.D 622–1470 data set yields several statistically significant periodicities, for both low‐water (256; 75.9; 52.6; 38; 28.9; 20.9; 18.5 and 13.4 yr) and flood levels (75.9; 33.6; 21.4; 14.7; 13.7; 9.7 and 8.1 yr). Evolutionary Multi Taper Method analysis suggests that shifts or disappearances of spectral peaks occur in sub‐intervals of the studied time span. This is noticeable for the low frequency peaks in the sub‐interval A.D. ∼950 ‐ ∼1250 which corresponds to the Medieval Warm Period in Europe. By contrast, a remarkable time stability is observed for the 5 yr period, that could confirm the existence of a robust ENSO‐like forcing during the studied period.