Thermal stress during heat waves and cold spells in Poland

Abstract

The study objective was the determination of the temporal and spatial variability/changes in the occurrence of heat waves and cold spells in Poland, and characteristics of biometeorological conditions during their occurrence based on the Universal Thermal Climate Index (UTCI). The research was based on data provided by the Institute of Meteorology and Water Management – National Research Institute from the period 1966–2021 for 37 stations in Poland. A heat wave was (HW) defined as a sequence of at least 3 days with maximum daily air temperature >30.0 °C, and a cold spell (CS) as a sequence of at least 3 days with maximum daily air temperature <-10.0 °C. After identifying HWs and CSs, the pattern of their occurrence was determined, i.e. their number and duration, first and last day of HWs and CSs, and the longest HW and CS. The analyses were performed for each station. Characteristics of biometeorological conditions were conducted based on the UTCI. Daily UTCI values provided the basis for the calculation of mean index values for individual HWs and CSs. Those with the highest and lowest mean UTCI were identified, as well as their days with the maximum and minimum UTCI values. The frequency of occurrence of individual classes of thermal stress during HWs and CSs was also determined. The study showed more and more frequent occurrence of HWs in Poland. Regions of Poland the most prone to the occurrence of HWs were the southern and central-western regions. They were also regions in which HWs were characterised by some of the highest UTCI values. The analysed years also showed high variability of occurrence of CSs both in temporal and spatial terms. The highest number and the longest CSs were recorded until the end of the 1980's. The study showed that the most strenuous biometeorological conditions were recorded in east, and particularly north-east Poland.