Extreme air temperature in Toruń (Poland), 1871–2020

Extreme air temperatures in Toruń were analysed for the period 1871–2020. The air temperature data were collected from data of the Prussian, German and Polish (Archives of the Institute of Meteorology and Water Management − National Research Institute) networks. Possible deficiencies in the monthly average data were supplemented by the method of constancy of differences based on data from the station in Bydgoszcz (correlation of air temperature data from Bydgoszcz and Toruń reaches 0.99 and is statistically significant). The data was then homogenised using AnClim software (Štěpánek, 2008). Based on quantile thermal classification criteria (Czernecki & Miętus, 2011), months, seasons and years were determined to be: extremely warm (>95.00 percentile), anomalously warm (90.01–95.00), very warm (80.01–90.00), warm (70.01–80.00), slightly warm (60.01–70.00), normal (40.01–60.00), slightly cool (30.01–40.00), cool (20.01–30.00), very cool (10.01–20.00), anomalously cold (5.00–10.00), extremely cold (<5). Temperature values for individual intervals were determined for each month, season and year separately.

In the period 1871–2020, the average annual air temperature in Toruń was 7.8 °C. In the annual cycle, the air temperature values were highest in July (18.3 °C) and lowest in January (˗2.4 °C). In the analysed period, the average annual air temperature shows a statistically significant trend of +0.1 °C per decade. For more detailed analyses, the research period was divided into fifty-year sub-periods. For the subperiod 1871–1920, there were no years classified as very, anomalously or extremely warm. The period 1921–70 was characterised by almost 50% frequency of years below the 40.00 percentile (<7.56 °C). In the last fifty years of the study period (1971–2020), there were no extremely cold years, while years classified as warm (all classes above the 60.00 percentile; >8.10 °C) have an almost 60% frequency.

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

References:

Czernecki B., Miętus M., 2011. Porównanie stosowanych klasyfikacji termicznych na przykładzie wybranych regionów Polski [Comparison of thermal classification for selected regions of Poland]. Przegląd Geofizyczny, z. 3–4, 201–227.

Štěpánek, P., 2008. AnClim - software for time series analysis: Dept. of Geography, Fac. of Natural Sciences, MU, Brno. 1.47 MB. http://www.climahom.eu/AnClim.html.