
Fig. 1
The course of the average annual – (A) and seasonal – (B) values of air temperature in Poznań in years 2011–2020 with the annual trend line.
Table 1
The average annual values of chosen meteorological elements in Poznań in years 2011–2020.
| Year | Cloudiness [%] | Precipitation [mm] | Snow cover [cm] | Insolation [h] | Relative humidity [%] | Vapour pressure deficit [hPa] |
|---|---|---|---|---|---|---|
| 2011 | 60 | 475 | 6 | 2030 | 76 | 9.6 |
| 2012 | 65 | 664 | 174 | 1900 | 79 | 10.0 |
| 2013 | 68 | 595 | 632 | 1721 | 78 | 9.7 |
| 2014 | 66 | 558 | 28 | 1962 | 77 | 10.2 |
| 2015 | 63 | 438 | 19 | 2036 | 72 | 9.1 |
| 2016 | 67 | 608 | 47 | 1823 | 76 | 9.7 |
| 2017 | 71 | 668 | 41 | 1739 | 77 | 9.8 |
| 2018 | 60 | 373 | 34 | 2225 | 71 | 9.6 |
| 2019 | 65 | 393 | 26 | 2040 | 73 | 9.9 |
| 2020 | 65 | 492 | 0 | 1518 | 73 | 9.7 |
| Mean | 65 | 526 | 101 | 1613 | 75 | 9.7 |
Table 2
Average monthly, seasonal and annual soil temperature [°C] at various depths in Poznań in 2011–2020.
| Months | Depth [cm] | ||||
|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |
| I | 0.3 | 0.7 | 1.0 | 1.7 | 3.0 |
| II | 0.6 | 0.9 | 0.9 | 1.2 | 2.2 |
| III | 4.3 | 4.8 | 4.4 | 3.9 | 3.8 |
| IV | 10.8 | 11.5 | 10.6 | 9.3 | 8.1 |
| V | 16.7 | 17.6 | 16.6 | 14.9 | 13.1 |
| VI | 21.3 | 22.1 | 21.1 | 19.4 | 17.5 |
| VII | 22.3 | 23.2 | 22.3 | 20.9 | 19.4 |
| VIII | 22.2 | 23.1 | 22.5 | 21.4 | 20.4 |
| IX | 16.5 | 17.4 | 17.2 | 17.1 | 17.4 |
| X | 10.4 | 11.1 | 11.1 | 11.6 | 12.7 |
| XI | 5.4 | 5.8 | 6.1 | 6.9 | 8.4 |
| XII | 2.2 | 2.5 | 2.8 | 3.4 | 4.8 |
| Spring | 10.6 | 11.3 | 10.5 | 9.3 | 8.3 |
| Summer | 21.9 | 22.8 | 22.0 | 20.6 | 19.1 |
| Autumn | 11.0 | 11.6 | 11.7 | 12.1 | 13.0 |
| Winter | 1.0 | 1.4 | 1.5 | 2.1 | 3.3 |
| Mean | 11.2 | 11.9 | 11.5 | 11.1 | 11.0 |

Fig. 2
Annual distribution of soil temperature at different depths in Poznań in the years 2011–2020.
Table 3
The standard deviation of monthly average soil temperature [°C] at various depths in Poznań in 2011–2020.
| Months | Depth [cm] | ||||
|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |
| I | 2.8 | 2.4 | 2.0 | 1.4 | 1.0 |
| II | 3.7 | 3.2 | 2.7 | 2.0 | 1.3 |
| III | 4.7 | 4.1 | 3.3 | 2.5 | 1.9 |
| IV | 6.1 | 5.3 | 4.2 | 3.0 | 2.3 |
| V | 6.2 | 5.3 | 4.1 | 2.8 | 2.0 |
| VI | 6.3 | 5.1 | 3.8 | 2.2 | 1.7 |
| VII | 5.7 | 4.7 | 3.5 | 2.0 | 1.3 |
| VIII | 5.9 | 4.8 | 3.5 | 2.0 | 1.4 |
| IX | 5.4 | 4.6 | 3.5 | 2.4 | 1.7 |
| X | 4.3 | 3.8 | 3.0 | 2.2 | 1.7 |
| XI | 3.2 | 2.9 | 2.5 | 1.9 | 1.5 |
| XII | 2.6 | 2.3 | 1.9 | 1.3 | 1.0 |
Table 4
Average monthly, seasonal and annual values of the thermal gradient [°C · cm−1] in Poznań in 2011–2020.
| Months | Soil level [cm] | |||
|---|---|---|---|---|
| 5–10 | 10–20 | 20–50 | 50–100 | |
| I | 0.08↓ | 0.03↓ | 0.03↓ | 0.03↓ |
| II | 0.07↓ | 0.00↓ | 0.01↓ | 0.02↓ |
| III | 0.10↓ | −0.04↑ | −0.02↑ | 0.00↓ |
| IV | 0.14↓ | −0.08↑ | −0.05↑ | −0.02↑ |
| V | 0.17↓ | −0.10↑ | −0.06↑ | −0.04↑ |
| VI | 0.16↓ | −0.10↑ | −0.06↑ | −0.04↑ |
| VII | 0.18↓ | −0.08↑ | −0.05↑ | −0.03↑ |
| VIII | 0.19↓ | −0.06↑ | −0.04↑ | −0.02↑ |
| IX | 0.18↓ | −0.02↑ | 0.00↓ | 0.01↓ |
| X | 0.13↓ | 0.01↓ | 0.02↓ | 0.02↓ |
| XI | 0.09↓ | 0.02↓ | 0.03↓ | 0.03↓ |
| XII | 0.07↓ | 0.02↓ | 0.02↓ | 0.03↓ |
| Spring | 0.14↓ | −0.07↑ | −0.04↑ | −0.02↑ |
| Summer | 0.18↓ | −0.08↑ | −0.05↑ | −0.03↑ |
| Autumn | 0.13↓ | 0.004↓ | 0.01↓ | 0.02↓ |
| Winter | 0.07↓ | 0.02↓ | 0.02↓ | 0.02↓ |
| Mean | 0.13↓ | −0.03↑ | −0.01↑ | 0.003↓ |
Table 5
Values of the 1st empirical percentile of daily mean soil temperature (°C) at various depths in Poznań during the period November–March (2011–2020).
| Months | Depth [cm] | ||||
|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |
| I | −1.7 | −0.9 | −0.3 | 0.7 | 2.1 |
| II | −0.6 | −0.3 | −0.1 | 0.7 | 2.0 |
| III | 1.5 | 2.0 | 1.8 | 1.8 | 2.4 |
| XI | 1.8 | 2.3 | 2.9 | 4.3 | 6.3 |
| XII | 0.6 | 1.0 | 1.5 | 2.6 | 4.2 |
Table 6
Mean annual number of days with soil temperature <0°C and >5°C at various depths in Poznań (2011–2020).
| Temperature [°C] | Depth [cm] | ||||
|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |
| ≤0 | 19 | 7 | 5 | 0 | 0 |
| ≥5 | 243 | 246 | 246 | 249 | 258 |
Table 7
Average start and end dates and the length of the particular periods with temperature thresholds at various depths in Poznań (2011–2020).
| Temperature threshold [°C] | Depth [cm] | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |||||||||||
| Start date | End date | Length (days) | Start date | End date | Length (days) | Start date | End date | Length (days) | Start date | End date | Length (days) | Start date | End date | Length (days) | |
| >0 | 14.02 | 20.01 | 341 | 27.01 | 21.01 | 360 | 27.01 | 22.01 | 361 | – | – | 365 | – | – | 365 |
| >2.5 | 3.03 | 11.12 | 279 | 27.02 | 14.12 | 286 | 1.03 | 18.12 | 286 | 1.03 | 31.12 | 295 | 2.02 | 13.01 | 345 |
| >5 | 19.03 | 18.11 | 245 | 17.03 | 21.11 | 250 | 19.03 | 23.11 | 250 | 22.03 | 30.11 | 254 | 25.03 | 13.12 | 264 |
| >6 | 24.03 | 9.11 | 231 | 21.03 | 12.11 | 237 | 24.03 | 16.11 | 238 | 28.03 | 22.11 | 240 | 1.04 | 4.12 | 248 |
| >8 | 2.04 | 28.10 | 210 | 30.03 | 1.11 | 217 | 2.04 | 2.11 | 215 | 8.04 | 6.11 | 213 | 15.04 | 18.11 | 218 |
| >10 | 11.04 | 17.10 | 190 | 8.04 | 20.10 | 196 | 12.04 | 21.10 | 193 | 20.04 | 24.10 | 188 | 28.04 | 2.11 | 189 |
| >12 | 22.04 | 6.10 | 168 | 19.04 | 10.10 | 175 | 23.04 | 10.10 | 171 | 1.05 | 12.10 | 165 | 9.05 | 19.10 | 164 |
| >15 | 7.05 | 21.09 | 138 | 3.05 | 25.09 | 146 | 8.05 | 25.09 | 141 | 17.05 | 26.09 | 133 | 29.05 | 29.09 | 124 |
Table 8
The sum of air temperature and soil temperatures (°C) at various depths in Poznań in years 2011–2020.
| Temperature threshold [°C] | Height 200 cm a.g.l. | Depth [cm] | ||||
|---|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | ||
| >5 | 3641 | 3852 | 4069 | 3933 | 3736 | 3595 |
| >6 | 3482 | 3792 | 4019 | 3860 | 3653 | 3551 |
| >8 | 3400 | 3644 | 3849 | 3724 | 3532 | 3370 |
| >10 | 3281 | 3469 | 3694 | 3528 | 3322 | 3161 |
| >12 | 3026 | 3229 | 3426 | 3293 | 3041 | 2864 |
| >15 | 2812 | 2773 | 3024 | 2836 | 2537 | 2371 |
Table 9
Average values of soil temperature [°C] during the day at various depths in Poznań in 2011–2020.
| Depth [cm] | Hours | |||
|---|---|---|---|---|
| 0 UTC | 6 UTC | 12 UTC | 18 UTC | |
| 5 | 8.7 | 8.9 | 15.6 | 11.7 |
| 10 | NA | 9.1 | 14.0 | 12.5 |
| 20 | NA | 9.8 | 12.1 | 12.7 |
| 50 | NA | 11.11 | 10.9 | 11.4 |
| 100 | NA | NA | 11.0 | NA |
[i] NA – not available.
Table 10
Values of absolute ground temperature extremes [°C] at various depths and dates of their occurrence in Poznań in 2011–2020.
| Depth [cm] | 6 UTC | 12 UTC | 18 UTC | |||
|---|---|---|---|---|---|---|
| MIN | MAX | MIN | MAX | MIN | MAX | |
| 5 | −12.2 | 28.6 | −8.2 | 44.0 | −10.41 | 34.8 |
| 6.12.2012 | 12.6.2019 | 7.2.2012 | 26.6.2019 | 6.2.12 | 26.6.2019 | |
| 10 | −11.0 | 26.1 | −8.4 | 36.0 | −9.4 | 33.6 |
| 6.12.2012 | 10.8.2018 | 6.2.2012 | 1.8.2018 | 6.2.12 | 26.6.2019 | |
| 20 | −9.4 | 27.1 | −8.6 | 30.5 | −7.8 | 32.2 |
| 6.12.2012 | 10.8.2018 | 6.2.2012 | 1.8.2018 | 6.2.12 | 1.8.2018 | |
| 50 | −5.2 | 26.8 | −5.5 | 26.3 | −5.1 | 26.9 |
| 7.12.2012 | 10.8.2018 | 7.2.2012 | 10.8.2018 | 7.2.12 | 3.8.2018 | |
| 100 | NA | NA | −0.0 | 23.9 | NA | NA |
| 12.2.2012 | 10.8.2018 | |||||

Fig. 3
The course of the temperature for individual soil levels in Poznań in the years 2011–2020 with the trend line.
Table 11
The correlation coefficient of the soil temperature at particular depths and selected meteorological elements in Poznań in 2011–2020.
| Meteorological element | Depth [cm] | ||||
|---|---|---|---|---|---|
| 5 | 10 | 20 | 50 | 100 | |
| Air temperature (2 m a.g.l.) | 0.96 | 0.81 | 0.78 | 0.73 | 0.421 |
| Cloudiness | −0.17 | −0.08 | −0.08 | −0.06 | 0.031 |
| Insolation | 0.54 | 0.60 | 0.56 | 0.52 | 0.441 |
| Snow cover | −0.12 | −0.10 | −0.09 | −0.08 | −0.041 |
| Humidity | −0.60 | −0.62 | −0.56 | −0.47 | −0.451 |
| Precipitation | 0.02 | 0.01 | 0.01 | 0.03 | −0.004 |
| Vapor pressure deficit | 0.79 | 0.77 | 0.71 | 0.62 | 0.531 |