EFFECT OF THE NORTH ATLANTIC OSCILLATION ON WATER LEVEL FLUCTUATIONS IN LAKES OF NORTHERN POLAND

The paper presents an analysis of correlations between water levels in Polish lakes and the rate of the North Atlantic Oscillation (NAO) in the years 1976-2010. The detailed analysis of the spatial variability of the effect of NAO on water levels in lakes concerned 19 lakes with statistically uniform hydrometric material. Two matrices were obtained for each of the lakes, composed of 156 coefficients of correlation calculated between monthly water stages and monthly and seasonal NAO indices. They provided the basis for performing two variants of classification of lakes by Ward's method. Four typological classes were distinguished for each variant. It was determined that stronger correlations occur in the case of water stages in lakes with seasonal than those with monthly NAO indices. The strongest effect of NAO on water stages is observed in the winter-spring period. Spatial variability of the effect has been recorded, resulting from the climatic conditions of a given region. Lakes located in the south-western part of the studied area constitute an evidently separate group. In the negative phase of NAO, they are distinguished by higher water stages in the winter-spring period. This may be associated with more frequent thaws during winters, and increased supply to lakes in the period.