DECADAL PERIODICITIES OF NILE RIVER HISTORICAL DISCHARGE (AD 622-1470) AND CLIMATIC IMPLICATIONS

The Roda Nilometer (Cairo, Egypt) has recorded more than 2,000 gauge r eadings, 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 l ow-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 M ulti Taper Method analysis suggests that shifts or disappearances of s pectral peaks occur in sub-intervals of the studied time span. This is noticeable for the low frequency peaks in the sub-interval A.D. simil ar to 950-similar to 1250 which corresponds to the Medieval Warm Perio d in Europe. By contrast, a remarkable time stability is observed for the 5 yr period, that could confirm the existence of a robust ENSO-lik e forcing during the studied period.