Current Climatic Conditions of Lake Regions in Poland and Impacts on Their Functioning Andrzej Górniak Contents 1 Introduction ................................................................................... 2 2 Material and Methods ......................................................................... 3 3 The Climate of Poland and Its Changes ...................................................... 4 3.1 Climatic Conditions of Poland ......................................................... 4 3.2 Climate of the Polish Lakelands ....................................................... 6 4 Polish Lakes Under Climatic Changes ....................................................... 11 4.1 Lake Water Storage Changes ........................................................... 11 4.2 Lake Water Temperature Regime and Recent Tendency .............................. 15 4.3 Predicted Climate Change Impact on Lake Functioning .............................. 20 5 Conclusions ................................................................................... 23 References ......................................................................................... 23 Abstract The condensed characteristics of the climate of Poland are presented with particular emphasis on the areas of lake districts. More detailed studies were provided on 19 lakes with daily hydrological and thermic observations in the calendar years 20002016. Climate warming is clearly observed in observational temperature data, with increases of 0.20.4 C per decade. Slightly lower air tem- peratures and a higher annual sum of precipitation in relationship to neighboring regions are specic for the Polish Lakelands. Mean annual air temperature in the eastern part is 1.5 C lower than in the western regions. Much greater variation of precipitation and climatic water balance was noted, where the Wielkopolskie and Lubuskie Lake Districts have a permanent water decit that is not observed in the rest of the Lakelands. Polish postglacial lakes are characterized by generally small uctuations in water level, whereas variations in articially regulated lakes are higher than in lakes with a natural regime, as well as a higher frequency of decreasing water level trends. Only a few lakes have a statistically signicant increase of lake water temperature, mostly in northeastern Poland. A simulation indicated that in year 2050 the annual lake water temperature will be 1.11.9 C A. Górniak (*) Department of Hydrobiology, Institute of Biology, University of Białystok, Białystok, Poland e-mail: hydra@uwb.edu.pl © Springer Nature Switzerland AG 2020 E. Korzeniewska, M. Harnisz (eds.), Polish River Basins and Lakes Part I, The Handbook of Environmental Chemistry 86, https://doi.org/10.1007/978-3-030-12123-5_1 1 hydra@uwb.edu.pl