Dry and wet spells variability in Poland in the period 1966-2023

The aim of this study is to present the spatial and temporal variability of the frequency of dry and wet days and dry and wet spells against the background of changes in precipitation and atmospheric circulation. The study is based on daily precipitation totals from 46 meteorological stations in Poland for the years 1966-2023. Additionally seven circulation indices were used: GBI, NAO, AO, EA, EA/WR. SCAND ana AMO. Dry days are defined as days without precipitation. Wet days are days with at least 1 mm of precipitation. It was shown that dry spells are much more common that wet spells, are longer and cover larger areas. Long term changes in annual characteristics of dry and wet days and spells are statistically insignificant. Only the length of the longest dry spell in the year increases. However, there are significant changes in their annual cycles. Spring is drier, especially April in summer months, precipitation decreases in the south and increases in the north, the same concerns dry day frequencies, November and December, symbols of gloomy rainy weather, are increasingly drier, rainy weather moved to January and February. Preliminary analysis of the impact of atmospheric circulation on the occurrence of dry and wet spells indicates high seasonal variability. In cold season, the Scandinavian type has the greatest influence, the presence of high pressure system over Scandinavia favors dry weather. In summer, precipitation and dry and wet spell occurrence are influenced by the NAO, AO, type EA and presence of high pressure system over Greenland. In spring and autumn, EA/WR type influences can be noticed.

This research was funded by National Science Center (NCN), grant number 2019/33/B/ST10/01136