Low-frequency sea-level variability along the Dutch coast

Abstract

In this study the contribution of the low-frequency residuals to the sea-level variability has been examined. This is done using 106-year old sea-level record obtained at Hoek van Holland. Computing the mean sea-level per season each year and the corresponding standard deviation one finds an increase in both these features of the sea-level record. The rise of the mean sea-level implies the effect of climate change. Moreover, it is found that the standard deviation in the sea-level, thus the intensity of variation, is the highest during fall and winter. This implies that the sea-level variability has a seasonal dependency. Furthermore, one finds an increase in the standard deviation on the long term. However, since a big part of the mean sea-level is influenced by tidal events, the increase in standard deviation is possibly linked to climate change in meteorological factors as has been found is in the study carried out by Gerkema and Duran-Matute(2017). With the use of the computational algorithms such as the Fast Fourier Transformation and the Wavelet Transformation one can extract the low-frequency residuals from the sea-level record. Inspired by the study of Gerkema and Duran-Matute(2017) a correlation between the wind speed and the low-frequency residuals have been found. Using the Wavelet Transformation it is found that the low-frequency residuals obtain the most energy during fall and winter, this empowers the finding that these low-frequency residuals are seasonal dependent. Moreover, when studying the low-frequency residuals closely it is found that the frequencies below 0.60 1 day obtain the most energy during fall and winter, especially the frequencies near 0.10 1 day . With these findings one can say that the contribution of the low-frequency signals, thus the low-frequency residuals, is correlated to meteorological events, such as the wind. Moreover, it is found that the variation in the low-frequency residuals is much smaller during spring and summer compared to the case during winter and fall. This seems not to be the case for the sea-level variability due to the tidal constituents and the high-frequency waves. Therefore, one may conclude that these low-frequency residuals contribute to a great extent in the standard deviation of the sea-level.