Less and thinner ice: seven decades of change in the ice cover of temperate lakes (Central Europe, Poland)

Ice cover is one of the most important parameters of lakes as it impacts many physical and biogeochemical processes beneath the ice. Understanding the temporal trends in ice cover duration and thickness is of great significance in terms of sustainable lake management in an era of climate change. In this study, lake ice observation data from the past seven decades (1954–2023) for four lakes in Central Europe, Poland, were collected and used for this purpose. The results showed that for all lakes, ice-on was postponed, delayed by 1.8 days per decade, and ice-off tended to be earlier by 3.6 days per decade. In this regard, ice cover duration reduced 6.5 days per decade, on average. Specifically, ice cover duration decreased in 40, 32, 40, and 45% for the four lakes, respectively. Moreover, for all lakes, the maximum thickness of ice cover decreased at an average rate of 3.3 cm per decade. Specifically, the maximum ice cover thickness decreased in 42, 47, 68, and 59% for the four lakes, respectively. Air temperature parameters (e.g., averaged air temperature during the ice cover duration and winter) are important controlling factors on lake ice cover, both for ice cover duration and the maximum thickness, while wind and rainfall play a minor role. With the rise of air temperature, lakes will have less and thinner ice cover. Mitigation measures shall be taken to reduce the impact of climate warming on lake ice.