Variability and course of occurrence of ice cover on selected lakes of the Gnieźnieńskie Lakeland (Central Poland) in the period 1976–2015

¹ Institute of Meteorology and Water Managament – National Research Institute, Podleśna 61, 01-673 Warszawa, Poland
² Department of Hydrology and Water Management, Adam Mickiewicz University, B. Krygowskiego 10, 61-680 Poznań, Poland

^* Corresponding author: rugosa@op.pl

Abstract

The paper presents the analysis of the course of ice phenomena on four lakes (Lednica, Żnińskie Duże, Biskupińskie, Powidzkie) in central Poland in the period 1976–2015. The obtained results show changes in their ice regime that occurred over the last 40 years. An advance of the term of decline of ice cover was determined (by 2.5 day·dec^-1on average for all lakes), as well as a reduction of duration of ice cover (by 4.4 day·dec^-1 on average for all lakes), and a decrease in its maximum thickness (by 2 cm·dec^-1 on average for all lakes). Such a situation should be associated with the observed warming, as confirmed by the course of air temperature for station Gniezno, where in the period of the winter half-year (November-April), an increase in temperature was recorded by 0.37^°C·dec^-1.