Biometeorological Conditions During Heat Events in Polish Cities in Summer Months from 2020 to 2024

This study analyzes biometeorological conditions during summer heat events in 11 cities located in different regions of Poland in the summer months from 2020 to 2024. Heat days (defined as days with a maximum temperature exceeding 30 °C) and heatwaves (defined as at least three consecutive days with a maximum temperature above 30 °C) were identified. Biometeorological conditions were assessed based on the Universal Thermal Climate Index (UTCI) and heart rate (HR), assuming a metabolic heat production of 135 W∙m−2 for an adult human. The indices were calculated using the BioKlima 2.6 software. The findings reveal that all cities experienced significant thermal stress during heat events. The maximum UTCI values during heat days indicated strong and very strong heat stress. During the most intense heatwaves, assessed using the Heat Wave Severity (HWS) index, these categories of heat stress occurred 20–30% of the time. Simultaneously, the mean daily heart rates exceeded the warning threshold of 90 beats per minute. Differences in biometeorological conditions were found between urban centers and places located outside the center, where strong heat conditions occurred less frequently. The results indicate that biometeorological conditions imposing thermal stress on the human body were present in all Polish cities during the analyzed five-year period. In Warszawa, Wrocław, and Rzeszów, heatwaves and heat stress occurred annually.