Key Contributors to Changes in Ice Phenology and Composition in Lowland Polish Lakes During 1983–2023: Climatic Variables and Lake Morphometry

Abstract Significant spatial and temporal differences in the pattern and magnitude of lake ice retreat have been widely observed, but the reasons for them remain unclear. Besides, changes in ice cover composition have rarely been revealed owing to a lack of long‐term observation. To fill these gaps, the MyLake model, combined with 40 years of observational data, was used to investigate the ice changes in Polish lowland lakes. The black ice decline is the significant change in all lakes, while the white ice is flat with extremely minor trends but remarkable annual and seasonal variability, largely attributed to the warming air temperature and varied changes in both amount and pattern of winter precipitation. Delayed freeze‐up, advancing break‐up, and thinned ice cover were all evident but differed among lakes. Model experiments indicated that changes in freeze‐up and break‐up timing and ice thickness are primarily driven by air temperature and are also mediated mainly by changing winter solar insolation and precipitation. Inter‐lake differences were demonstrated to be caused by differences in both lake morphometry and climate changes. Specifically, lake morphometry (especially the depth) constrains the freeze‐up and break‐up timing and trends of freeze‐up rather than break‐up trends. When the impacts of lake morphometry are removed, inter‐lake differences in phenological timings and their trends are explained by regional differences in winter air temperature, precipitation/snow, and their temporal changes.