Variability of Hot Days in the Middle Latitudes of Europe between 1973 and 2024

Hot days gain great attention around the world for their wide impacts on water resources, agriculture, society productivity, biosystems, and public health. We explore daily data from weather stations, the global surface summary of day product produced by the National Centers for Environmental Information of the United States, to determine changes in the monthly frequency of hot days (maximum daily temperature above 35 degrees Celsius) in Western, Central, and Eastern Europe. The monthly percentages show increasing trends in June, July, and August between 1973 and 2024. They are positively correlated with the monthly average geopotential height at 500hPa: Correlation coefficients computed with monthly ERA5 reanalysis data over the three regions lie between 0.54 and 0.78 (p