Thermal comfort conditions of the Dnipropetrovsk region in the modern period

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The study aims to investigate the thermal comfort conditions of the Dnipropetrovsk region for the period 1991–2020, based on modern approaches. The physiologically equivalent temperature (PET) was used to determine the thermal bioclimate in the Dnipropetrovsk region. PET calculations were performed using the RayMan model, which is a microscale model for calculating radiation fluxes in simple and complex environments. Daily data measured at 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00 UTC from six weather stations of the meteorological network of the Ukrainian Hydrometeorological Centre (Dnipro, Kryvyi Rih, Pavlohrad, Nikopol, Komisarivka, Synelnykove) for the period 1991–2020 were used to analyze thermal comfort conditions in the Dnipropetrovsk region. The study of the bioclimatic conditions of the Dnipropetrovsk region showed that in the winter months (December–February), extreme cold stress prevails, with a frequency of occurrence ranging from 94.5% to 99.8% across the region. Starting from the second decade of May until the second decade of September, heat stress of different intensities was observed in the region, with the highest frequency in the second decade of July, ranging from 39.1% in Dnipro to 50% in Nikopol. The highest frequency of strong and extreme heat stress was observed in the first decade of August, ranging from 10.7% to 17% in different parts of the region. During daytime hours, the highest frequency of extreme heat stress in the region was observed in the first decade of August, ranging from 5.1% to 13.3%. The daily variation of PET during the period with the most strenuous hot conditions throughout the year (July’s third decade and August’s first decade) was similar to the daily variation of air temperature, with minimum values after sunrise (03:00 UTC) and maximum values after midday (12:00 UTC). The most comfortable conditions were found in the morning and evening hours (06:00 UTC and 18:00 UTC, respectively). In the city of Dnipro, the number of heat waves (HW) increased from 16 to 33 in the period 1991–2020 compared to the normal climatic period (1961–1990). The mean PET value during HW events in Dnipro during the period 1991–2020 was 39.7°C, while during the summer months, it was nearly 10°C lower (29.9°C).