Impact of climate change on the coastal water temperature of lagoons in the southern Baltic Sea in the period 1951–2020

The study examines long-term trends in water surface temperature (WST) in the Vistula and Szczecin Lagoons within the southern Baltic Sea from 1951 to 2020. Based on in situ data, temperature variability was assessed using both parametric linear regression and the non-parametric Mann-Kendall test. The results reveal a statistically significant increase in water temperatures, particularly during spring and winter. The average warming rate reached 0.23°C and 0.26°C per decade in the Vistula and Szczecin Lagoons, respectively. A strong correlation (𝑟 = 0.60–0.93) was observed between air and surface water temperature. Extreme temperature events are becoming more frequent, with the lowest percentile values rising markedly over time. Winter temperatures exceeding 3°C are now common, and ice cover has diminished or disappeared. These trends highlight the regional impacts of climate change on coastal lagoon ecosystems and their seasonal dynamics. The findings provide valuable insights for future monitoring and management of vulnerable brackish water environments.