Early warning for sunny-day flooding in the East Coast of the United States: global implications

Inspired by Walter Munk’s proposition of an ‘orbital gap’ in climate variability, this study seeks to determine the linkage between cycles within such orbital gap and ‘sunny-day’ coastal flooding.  The orbital gap represents astronomical variability between the nodal lunar cycle (18.6 y) and the shortest Milankovitch cycle (Earth’s axial precession, ~20,000 y).  Such astronomical variability arises from Earth-Moon-Sun orbital non-linear interactions, some of them represented by multiples of the lunar nodal cycle and the radiational periods of the sun (solar activity, ~10-11 y). Periodicities <100 y associated with these astronomical effects are fitted in this study to the signal of daily maximum in water levels of tide stations in the eastern United States with records greater than 100 y. In Boston, for example, the lunar nodal cycle by itself explains 73% of the variance of the daily maxima in water level.  Adding twice, thrice and six times the nodal cycle, plus twice the solar period, yields a fit that explains 81% of the variance. This fit is repeated for other locations on the eastern United States and allows projections for periods of most vulnerability to sunny-day flooding in the rest of the 21^st century. This approach is likely to be applicable in other parts of the world to provide early warnings of susceptibility for ocean-induced coastal zone flooding.