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The historical records of the low‐ and high‐water levels of the Nile River are among the longest climatic records that have near‐annual resolution. There are few gaps in the first part of the records (A.D. 622–1470) and larger gaps later (A.D. 1471–1922). We apply advanced spectral methods, Singular‐Spectrum Analysis (SSA) and the Multi‐Taper Method (MTM), to fill the gaps and to locate interannual and interdecadal periodicities. The gap filling uses a novel, iterative version of SSA. Our analysis reveals several statistically significant features of the records: a nonlinear, data‐adaptive trend that includes a 256‐year cycle, a quasi‐quadriennial (4.2‐year) and a quasi‐biennial (2.2‐year) mode, as well as additional periodicities of 64, 19, 12, and, most strikingly, 7 years. The quasi‐quadriennial and quasi‐biennial modes support the long‐established connection between the Nile River discharge and the El‐Niño/Southern Oscillation (ENSO) phenomenon in the Indo‐Pacific Ocean. The longest periods might be of astronomical origin. The 7‐year periodicity, possibly related to the biblical cycle of lean and fat years, seems to be due to North Atlantic influences.
Kondrashov et al. (Sun,) studied this question.