Extreme precipitation in Toruń (Poland), 1871-2020

Extreme precipitation in Toruń was analysed for the period 1871–2020. The precipitation series was collected from data of the Prussian, German and Polish networks (Archives of the Institute of Meteorology and Water Management National Research Institute). Possible deficiencies in the monthly average data were supplemented by the method of constancy of quotients (precipitation) based on data from the station in Bydgoszcz. The correlation of data from Bydgoszcz and Toruń reaches 0.99 and is statistically significant. The precipitation series was then homogenised using AnClim software. Minimum and maximum absolute values were determined for all analysed parameters. Anomalies of averages and monthly, seasonal and annual sums were determined with respect to the reference period 1871–2020. Based on the percentage criterion, months, seasons and years were determined to be extremely dry (<50% of the average sum for the month/season/year, respectively), extremely wet as >150%, and average a 90–110%.

In the period 1871–2020, the average annual precipitation in Toruń amounted to 518.2 mm. In the course of the year, the precipitation totals were highest in July (78.2 mm) and lowest in February (25.1 mm). The variability of rainfall from year to year is clear and significant in selected subperiods, but precipitation in Toruń does not indicate a clear and statistically significant trend. This phenomenon is typical for precipitation in Poland. The occurrence of an extremely dry or wet year is determined primarily by the precipitation of the summer season, which on average accounts for about 40% of annual precipitation. In the case of seasons from 2010 onwards, wetter winters are observed. In the case of other seasons, wetter and drier periods can be indicated, but without a clear long-term trend. Using the percentage criterion, extremely warm, dry periods were identified at the end of the 1930s, in the late 1940s to early 1950s, and in the late 1980s to early 1990s. The beginning of the 1940s can be described as extremely cold and humid, as can the late 1970s to early 1980s.

The research was funded by the National Science Centre, Poland; Project No. 2020/37/B/ST10/00710.