Current Climatic Conditions of Lake Regions in Poland and Impacts on Their Functioning

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 2000–2016. Climate warming is clearly observed in observational temperature data, with increases of 0.2–0.4°C per decade. Slightly lower air temperatures and a higher annual sum of precipitation in relationship to neighboring regions are specific 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 deficit that is not observed in the rest of the Lakelands. Polish postglacial lakes are characterized by generally small fluctuations in water level, whereas variations in artificially 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 significant increase of lake water temperature, mostly in northeastern Poland. A simulation indicated that in year 2050 the annual lake water temperature will be 1.1–1.9°C higher than at present. We can expect more evident changes in lake functioning in spring and summer, shifting lakes toward higher trophy, but dystrophic lakes will remain more humic when their hydrology is stable.