Changes in Sea Level, Storm and Wave Conditions, and Ice Cover—Over 70 Years of Observation in the Southern Baltic Sea

This study demonstrates changes in the hydrodynamic regime associated with climate change in the southern Baltic over more than 70 years. The analysis of long-term data about sea level, the occurrence of ice cover, waves, and storm surges in the southern Baltic enabled the identification of spatiotemporal variability, including the detection of changes in intensity, frequency, and repeatability of these phenomena. The sea level in the southern Baltic rose by approximately 1 cm/decade from 1886 to 1955. Then, from 1956 to 2019, intensification was observed, and the sea level rose by 1.6 cm/decade and 1.9 cm in the western and eastern parts, respectively. The most intense decadal sea level change in 1955–2019 occurred in March (3.1 cm) and January (2.5 cm), while from July to December, it was at 0.8–1.3 cm. Statistical direct correlation analyses using Spearman’s rank method showed a weak but statistically significant relationship between the mean daily sea level with water temperature and air temperature measured at the same stations. An increase in the frequency of storms in individual decades and a decrease in the number of days with ice was demonstrated. There was no clear trend in the wave conditions regime during the period covered by the analysis in 1980–2021.