Past and future changes in sea level near the Estonian coast in relation to changes in wind climate

Abstract

The dependence of sea level on past and future climatological conditions is investigated in nearly tideless semi-enclosed sub-basins of the Baltic Sea using trend analysis of the tide gauge data for the period of 1924–2003 and hydrodynamic modelling. The results suggest that in addition to the effect of eustatic rise in mean sea level and its partial compensation by isostatic land uplift, the water level has risen by up to 6 cm near the Estonian coast during the last fifty years, probably due to changes in wind climate. The sea-level increase was concentrated in the period from November to March. It is in good correlation with increasing trends in local storminess and in higher intensity of westerlies, as described by AO and NAO indices. For the future sea level, a set of sensitivity and scenario runs considering possible future changes in wind climate was performed using a 2D hydrodynamic model with a 1-km grid-step. The scenario runs show that if the intensity of westerlies continues to grow (with less than 20% annual mean wind speed increase) the local annual mean sea level rise up to 5–6 cm can occur in some windward bays of the Gulf of Riga. The rise can be up to 9–11 cm in winter months, while in summer the sea level rise is unlikely. Also, increase in variability and extremes can be expected.