Tidally driven interannual variation in extreme sea level frequencies in
the Gulf of Maine
Abstract
Astronomical variations in tidal magnitude can strongly modulate the
severity of coastal flooding on daily, monthly, and interannual
timescales. Here, we present a new quasi-nonstationary skew surge joint
probability method (qn-SSJPM) that estimates interannual fluctuations in
flood hazard caused by the 18.6 and quasi 4.4-year modulations of tides.
We demonstrate that qn-SSJPM-derived storm tide frequency estimates are
more precise and stable compared with the standard practice of fitting
an extreme value distribution to measured storm tides, which is often
biased by the largest few events within the observational period.
Applying the qn-SSJPM in the Gulf of Maine, we find significant tidal
forcing of winter storm season flood hazard by the 18.6-year nodal
cycle, whereas 4.4-year modulations and a secular trend in tides are
small compared to interannual variation and long-term trends in
sea-level. The nodal cycle forces decadal oscillations in the 1% annual
chance storm tide at an average rate of ±13.5 mm/y in Eastport, ME; ±4.0
mm/y in Portland, ME; and ±5.9 mm/y in Boston, MA. Currently (in 2020),
nodal forcing is counteracting the sea-level rise-induced increase in
flood hazard; however, in 2025, the nodal cycle will reach a minimum and
then begin to accelerate flood hazard increase as it moves toward its
maximum phase over the subsequent decade. Along the world’s
meso-to-macrotidal coastlines, it is therefore critical to consider both
sea-level rise and tidal non-stationarity in planning for the transition
to chronic flooding that will be driven by sea-level rise in many
regions over the next century.