The paper analyses changes in potential evaporation E₀ (mm) in north-western Poland in the years 1952–2018. E₀ (mm) has been calculated according to Ivanov’s formula based on the monthly values of air temperature (t, °C) and relative air humidity (f, %) for six weather stations of the Institute of Meteorology and Water Management. The data were collected using the Statistica software ver. 13 and the QGIS software ver. 3.80. The results indicate statistically significant trends in the increase of E₀ during the period 1952–2018, and that it is particularly high during the spring and summer months, which should be associated with a statistically significant increase in air temperature and a decrease in relative humidity at all examined stations. The results also indicate an exceptionally high increase in evaporation since the end of the 20th century and in the 21st century, which reflects a potentially higher risk of permanent changes in hydrological conditions. The research results point to the major role of climatic factors in the often-dramatic decreases in water resources observed in the 21st century, particularly in lakes and small watercourses. The progressing reduction of water resources may cause permanent changes in physical and chemical conditions in waterbodies.

The objective of research involved the comparison of daily and seasonal courses of thermal stress occurring in Central Europe depending on the inflowing air mass. The analysis used data from Warsaw (1991–2000), including air temperature (°C), water vapour pressure (hPa), wind speed (m s⁻¹) and cloud cover (%). Universal thermal climate index was calculated and subsequently averaged for the individual months and four types of atmospheric air masses: polar maritime (mP), arctic(A), polar continental (cP) and tropical (T). The studies analysed differences in daily patterns of the averaged values of universal thermal climate index between air masses and determined the frequency of days with various types of thermal stress in individual air masses. The analyses indicated that under the conditions of Central Europe, the highest daily variance of biothermal conditions occurs between the masses of cP and T in the spring and autumn. Considerably greater diversity of biothermal conditions was observed between the masses during daytime compared with nighttime, especially in the warm half of the year. The thermal stress, which can be encountered in Central Europe, ranges from an “extreme cold stress” in winter at night and early morning hours to “very strong heat stress” in summer at noon. Extreme thermal stress is related primarily to the masses of cP, A and T. The most optimal biothermal conditions occur during the advection of mP air.

The work describes diurnal meteorological and biometeorological conditions in June 2019 in the urban areas of Central Europe. UTCI, STI, Oh_H, WL, and OV indices were calculated based on 24-h data from Bydgoszcz (Poland) for hot days. The degree of risk connected with heat stress of different intensities, risk of hyperthermia, body water loss, and decreased oxygen volume was determined. The studies showed that June 2019 was an example of an extreme situation with a heatwave that generated high stress for the inhabitants of urban areas. The conditions were burdensome mostly due to “very strong” and “strong” heat stress and periodic risk of dehydration, situations that could quickly lead to overheating of the body and a decreased oxygen volume leading to stress.

Uciążliwość warunków odczuwalnych podczas dni upalnych przy różnej intensywności aktywności fizycznej (na przykładzie północno-zachodniej Polski)

Zarys treści. W pracy przedstawiono charakterystykę zagrożeń związanych z wysoką temperaturą powietrza występującą w godzinach okołopołudniowych w dniach upalnych, na podstawie analizy uniwersalnego wskaźnika obciążenia cieplnego (UTCI). Na podstawie wartości wskaźnika dla Kołobrzegu, Poznania i Krakowa z lat 2001-2018 obliczono jego średnie wartości, odchylenie standardowe, wartości minimalne i maksymalne, amplitudę, a także kwartyl dolny i górny oraz współczynnik skośności, w ujęciu wieloletnim i poszczególnych lat. Za pomocą jednoczynnikowej analizy wariancji ustalono czy wartości wskaźnika UTCI w południe w dniach upalnych różnią się istotnie w zależności od miesiąca. Ponadto określono częstość występowania obciążenia organizmu stresem ciepła o różnym nasileniu. Badania wykazały, iż w południe w dniach upalnych przeważał "umiarkowany" oraz "silny stres ciepła", chociaż mogło pojawić się także obciążenie "bardzo silnym stresem ciepła". Otrzymane wartości wskaźnika w większości kształtowały się powyżej średniej wieloletniej, co oznacza wysoki poziom