The characteristics of the diurnal pattern of biothermal conditions in the summer season in selected European cities

This paper examines the diurnal pattern of biothermal conditions in three summer months (June, July and August) from 2018 to 2022, in selected European cities and analyses their burden on the human body. The weather data provided the basis for calculating the following indices: Universal Thermal Climate Index, Subjective Temperature Index, Maximal Heart Rate, Insulation Predicted, Water Loos, Overheating Risk. The study determined the daily mean, minimum and maximum values of biothermal and thermophysiological indices and their diurnal patterns, analysed their spatial distribution using spatial interpolation, and determined the incidence of heat load, apparent temperature, acceptable level of physical activity, predicted thermal insulation of clothing, degree of dehydration, and risk of hyperthermia. Studies have shown that, in Europe during the summer, between 12 p.m. and 3 p.m., there may be a burden of very intense heat stress (particularly in July and August), with a subjective sensation described as “very hot”. The risk of dehydration is not significant; however, there is a notable risk of hyperthermia, which can occur even after 20 minutes of exposure in open areas. In southern Europe, from 9 a.m. to 3 p.m., beachwear would be sufficient to maintain thermal comfort, while in the north, especially at night-time, transitional season clothing is necessary. Analyses have also shown that, particularly in cities such as Madrid, Bucharest and Rome, physical exertion should be avoided during midday hours. Climate warming in Europe during the summer is a serious challenge that requires coordinated actions at the local, national and international levels.