Oscillatory modes of extended Nile River records (A.D. 622–1922)

Abstract

[1] 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 quasiquadriennial (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 ElNiño/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.

Support for global climate reorganization during the “Medieval Climate Anomaly”

“…The simulated 10-15% reduction in Ethiopian Highlands summer rainfall is in the range of the *10% reductions in Blue Nile flood discharge during medieval time indicated by documentary and lacustrine records (Hassan 1981;Kondrashov et al 2005;Hassan 2007; Fig. 3J; see also Halfman et al 1994; Appendix 1).…”

“…Instrumental monthly Nile discharge data are available from Aswan in southern Egypt since 1870 (Vörösmarty et al 1996), though not useful for this study after 1960, due to abstractions and dam construction. For the results reported here, we use the maximum level record (MAXFL) developed by Kondrashov et al (2005; Fig. 3J).…”

“…For summer, documentary measurements of Nile maximum flood level from Cairo ( Fig. 3J) indicate maximum annual flood levels tended to be lower during the MCA than during the LIA (Hassan 1981;Kondrashov et al 2005;Hassan 2007). As described in Appendix 1, converting the maximum flood level record to flood season discharge at Aswan, and applying corrections for channel aggradation, indicates flood season Nile discharge was reduced by about 10% during the MCA.…”

Multidecadal to millennial marine climate oscillations across the Denmark Strait (~ 66° N) over the last 2000 cal yr BP

“…11) and 15 yr spaced data for 2322. Trends in the data were detected by using Singular Spectra Analysis (SSA) (Ghil et al, 2002), and the residuals from the trends were processed using SSA and MultiTaper Method (MTM) analyses (Mann and Lees, 1996;Kondrashov et al, 2005). Given the warnings about age models (Telford et al, 2003) the 30 yr equi-spaced time series are at the limit of acceptance, although the Nyquist frequency essentially restricts the recognition of meaningful periodicities to a century or more.…”

“…The residuals from the trend for 2322 show significant (95 %) oscillatory modes (Vautard and Ghil, 1989;Kondrashov et al, 2005) at 192 yr (175 yr MTM) and weaker modes at 110 and 76 yr. The reconstructed time series based on these modes (Fig.…”