Abstract
Abstract. Mean sea level (MSL) is rising worldwide, and correlated changes in ocean tides are also occurring. This combination may influence future extreme sea levels, possibly increasing coastal inundation and nuisance flooding events in sensitive regions. Analyses of a set of tide gauges in Hong Kong reveal complex tidal behavior. Most prominent in the results are strong correlations of MSL variability to tidal variability over the 31-year period of 1986–2016; these tidal anomaly correlations (TACs) express the sensitivity of tidal amplitudes and phases (M2, S2, K1, O1) to MSL fluctuations and are widely observed across the Hong Kong region. At a few important harbor locations, time series of approximations of the parameter δ-HAT, computed from combinations of the major tidal constituents, are found to be highly sensitive to MSL variability, which may further increase local flood levels under future MSL rise. Other open-water locations in Hong Kong only show TACs for some individual tidal constituents but not for combined tidal amplitudes, suggesting that the dynamics in enclosed harbor areas may be partially frequency dependent and related to resonance or frictional changes. We also observe positive correlations of the fluctuations of diurnal (D1) tides to semidiurnal (D2) tides at most locations in the region, which may lead to further amplified tidal ranges under MSL. It is demonstrated here that tidal changes in the Hong Kong coastal waters may be important in combination with MSL rise in impacting future total water levels.
Highlights
Ocean tides have long been thought of as a stationary process as they are driven by the gravitational forcing of the Sun and Moon whose motions are complex but highly predictable (Cartwright and Tayler, 1971)
The strongest positive M2 tidal anomaly correlations (TACs) are seen at Quarry Bay (+218±37 mm m−1) and at Tai Po Kau (+267±42 mm m−1) with a smaller positive TAC seen at Shek Pik (Fig. 3)
The TACs, D1/D2 relations, δ-Highest Astronomical Tide” (HAT), and the anomalous events in tidal amplitudes seen at the Quarry Bay and Tai Po Kau gauges show an amplified tidal response to mean sea level (MSL) fluctuations in these harbor regions as opposed to more open-water locations, where individual TACs were sometimes significant but the δ-HAT changes were less significant
Summary
Ocean tides have long been thought of as a stationary process as they are driven by the gravitational forcing of the Sun and Moon whose motions are complex but highly predictable (Cartwright and Tayler, 1971). Tides can exhibit short-term variability correlated to short-term fluctuations in MSL (Devlin et al, 2014, 2017a, b) These variabilities may influence extreme water level events, such as storm surge or nuisance flooding (Sweet and Park, 2014; Cherqui et al, 2015; Moftakhari et al, 2015, 2017; Ray and Foster, 2016; Buchanan et al, 2017). Such short-term extreme events are obscured when only considering long-term linear trends. Any significant additional shorter-term positive correlation between tides and sea level
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