Correlation of wind waves and sea level variations on the coast of\nthe seasonally ice-covered Gulf of Finland

Abstract

Abstract. Both sea level variations and wind-generated waves affect coastal flooding risks. The correlation of these two phenomena complicates the estimates of their joint effect on the exceedance levels for the continuous water mass. In the northern Baltic Sea the seasonal occurrence of sea ice further influences the situation. We analysed this correlation with 28 years (1992–2019) of sea level data, and four years (2016–2019) of wave buoy measurements from a coastal location outside the City of Helsinki, Gulf of Finland. The wave observations were complemented by 28 years of simulations with a parametric wave model. The sea levels and waves at this location show strongest positive correlation (τ\u2009=\u20090.5) for southwesterly winds, while for northeasterly winds the correlation is negative (−0.3). The results were qualitatively similar when only the open water period was considered, or when the ice season was included either with zero wave heights or hypothetical no-ice wave heights. We calculated the observed probability distribution of the sum of the sea level and the highest individual wave crest from the simultaneous time series. Compared to this, a probability distribution of the sum calculated by assuming that the two variables are independent underestimates the total water levels corresponding to one hour per 100 years by 0.1–1.2\u2009m. We tested three Archimedean copulas, of which the Gumbel copula best accounted for the mutual dependence between the two variables.\n