Vol. 123, No. 4 * Pages 409–576 * October - December 2019

The aim of the present paper was an attempt to detect the recurring fluctuations in the course of seasonal sums of precipitation in Poland. The basic material consisted of monthly sums of atmospheric precipitation obtained from 37 IMGW-BIP weather stations from the period 1951 – 2016, excluding the mountain areas. Spectral analysis was performed concerning precipitation sums in the four calendar seasons: spring (March – May), summer (June – August), autumn (September – November), winter (December – February). The results of the spectral analyses showed that the changes in seasonal precipitation sums recorded in the analyzed multiannual period occurred in numerous, statistically significant cycles, with a clear predominance of the cycles with the following length: 4.0, 4.6, 4.9, 5.3, 5.8, 6.4, and 7.1 years. It was found that the winter season is characterized by the most pronounced cyclicality (cycles of 6.4 years), whereas the spring season is marked by the highest variability in terms of periodicity.