Statistical assessment of annual patterns in coastal extreme wave conditions

Abstract

The annual cycle in extreme values of significant wave height is examined by transforming the timing ofthe storm peaks in a circular variable, with the aim of taking advantage of the many tests devised to explore uniformity on the circle. The use of four different but complementary uniformity tests makes possible a robust assessment of the annual cycle statistical significance. Seasonality of storms in a long time series of significant wave heights, measured in a coastal zone, is examined. The presence of a seasonal pattem is statistically beyond doubt.

Spatiotemporal Variability of Extreme Wave Storms in a Beach Tourism Destination Area

“…Furthermore, wave conditions undergo a clear seasonal pattern in the most energetic areas, the northern and western sides of the archipelago, with mild wave conditions from April to October and more severe situations from November to March. Regarding wave storm conditions on the north side of the archipelago, it has been observed that extreme wave events also exhibit a statistically significant seasonal behavior [11]. The tidal regime in the islands is mesotidal, with a semidiurnal tide pattern and a tidal range oscillating approximately between 0.5 m and 3 m, and a mean value close to 1.5 m [12].…”

“…To assess the existence of seasonal variations in the timing of wave storms throughout the annual period, the day of the calendar year on which the maximum significant wave height of a given storm occurred has been converted to an angular value, θ, assuming that the number of days per year is 365. Thus, in leap years, the data corresponding to 29 February have been removed [11].…”

“…The selection of these two tests from among the multitude of existing alternatives is due to the fact that the Rayleigh test is powerful only when it is possible to assume that the population distribution has only one mode, while the Kuiper test is specifically indicated in the case of multimodal distributions. More detailed information on these and other uniformity tests can be found in [11,29] and references therein.…”

“…Considering the importance of the occurrence of wave storms coinciding with high tide conditions, the minimum allowable temporal distance between storms, ISD min , was set at 48 h, which includes four low and high tide levels and is close to the average duration of atmospheric disturbances in the North Atlantic [11,17]. In the same vein, the minimum duration of the storm has been stated as the duration of a complete tidal cycle, D min = 12 h.…”