Relationship between air temperature change and southern Baltic coastal lagoons ice conditions

The relationship between air temperature (mainly winter, December-March) in Świnoujście, Gdynia, and Elbląg and ice parameters (dates of the first ice and disappearance of the last ice, the length of the ice season, number of days with ice, maximum ice height) of southern Baltic coastal lagoons (Szczecin, Puck, and Vistula) was investigated. Trends in these parameters were determined, too. The observation material comes from the archives of the Institute of Meteorology and Water Management and spanned the winters from 1950/51 through to 2019/20. Relationships between the selected ice parameters for the study basins and the values of air temperature were examined using correlation and regression methods. The regression equations and trends, as well as their correlation and determination coefficients, were determined. The statistical significance of these relationships was examined using the Fisher-Snedecor test. Strong correlations between ice parameters values and air temperature were obtained, characterized by high values of both correlation coefficients and statistical significance. All trends of ice parameters indicate mitigation of ice conditions. An acceleration in both temperature and ice condition mildening occurred in the late 1980s, and especially in the last years of the study period. These trends, except the first ice date, are statistically significant, some even at α < 0.001. The length of the ice season becomes significantly shorter, the number of days with ice and the maximum thickness is smaller, and the last ice is disappearing early. An increase in the correlation and determination coefficients and a characterized trend of ice parameters values towards the East was found. It shows the increased impact of a warming climate in this direction on the southern Baltic coast. Strong correlations and trends may be of prognostic significance.