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Time-series analysis on interannual variability of meteorological factors influencing sea level in the Southern Bight of the North Sea
Henkens, S. (2020). Time-series analysis on interannual variability of meteorological factors influencing sea level in the Southern Bight of the North Sea. MSc Thesis. Universiteit Antwerpen/Gent University/Vrije Universiteit Brussel: Antwerpen, Gent, Brussel. 83 pp.

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Documenttype: Doctoraat/Thesis/Eindwerk

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Abstract
    Temperature and sea level are primary indicators of global climate change (GCOSa,2019). Sea level variability on short time scales such as waves and tides can easily be averaged out as opposed to atmospherically induced interannual and decadal variability which is found to be irregular. The latter conceals the climatic trend and the fact that interannual variability usually is in the order of decimeters while climatic sea level rise is typically only estimated to be a few millimeters per year, complicates the analysis even further (Gerkema and Duran-Matute, 2017.This dissertation uses intelligible machine learning methods to gain insight into the monthly and annual mean sea level data that was obtained via the Permanent Service for Mean Sea Level (PSMSL) for the stations Ostend and Nieuwpoort. These stations lie in the southern bight of the North Sea. By utilising generalised additive models, the goal is to combine the advantage of decomposability of a simple linear model, with the added benefit of enhanced performance due to the estimation of more complex relationships between the independent and dependent variables. This 1) permits the formulation of formal relationships between factors in the Belgian Part of the North Sea (BPNS) that influence sea level variability and 2) increases the understanding of the mechanistic relationships of the physical forces that drive sea level variability at the Belgian coast. They also serve as the basis for the formation of new hypotheses for future research.What follows is a selection of the conclusions drawn from the results obtained in the present study: •Moderately positive linear relations were found for westerly winds and sea level in Ostend. Easterly winds correlate moderately negative with sea level. •Generalised additive models have shown promising potential to model annual and monthly mean sea level and to analyse time series of physical variables. •According to the models derived in the present study, sea level has risen approximately 2.8 mm/year during the time period 1979-2017. •The models for seawater temperature have not yielded a linear yearly trend. The results presented here show a seawater temperature change of -2 C/century between 1903-1913, +0.8 C/century between 1949-1965, +0.53 _C between 1950-1959, +4.6 C between 1979-2017 and +3.4 C between 2001-2019. •On average the wind energy has decreased between 1979-2017 with 0.53 J/s. However this could not be proven with a statistical significance of *p< 0:05.

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