Contemporary changes of climate in Poland: trends and variation in thermal and solar condition related to plant vegetation

Presented paper analyses climate trends in Poland in the second half of the 20th century. Measurements of climate elements were obtained from 5 meteorological stations evenly distributed over Poland (Szczecin 53°24’N–14°37’E, Wrocław 51°08’N–16°59’E, Łódź 51°44’N–19°24’E, Suwałki 54°08’N–22°57’E, Przemyśl 49°48’N–22°46’E). The variability of several indices conditioning the growth of plant vegetation was determined. Increase in the air temperature in the first three quartiles of the calendar year was detected. During November– December period the opposite tendencies were noted, however not statistically significant. The length of winter period shortened considerably, especially in western Poland. The warming caused substantial rise in potential evapotranspiration, the largest in April, May and August. Summer period has extended during the last five decades. Cumulative temperatures, calculated with respect to the 10°C threshold, also revealed an upward tendency. Sunshine duration totals increased – the highest increase was observed in the western Poland in May–June season. The length of vegetation season (> 5°C) did not change significantly during the 50-year period. There was only a slight tendency towards the earlier occurrence of both beginning and ending date of this season. The climate transformation in Poland, related undoubtedly to global warming, indicates possible intensification of vegetation growth due to more favourable solar and thermal conditions.