Heatwaves have been the most prominent hazard causing weather-related human fatalities over the past decades. The 2003 summer European heatwave alone caused up to 70 000 excess deaths over 4 months in central and western Europe. Increased mortality is the most drastic impact of heatwaves. However, exposure to hot days and nights can impact human health and well-being in various other ways, including ‘bad moods', feeling discomfort and getting sick, all factors reflected by ‘thermal comfort'.
The temperature in urban areas tends to be higher than the temperature in their rural surrounding areas, creating a city-specific phenomenon known as the urban heat island (UHI). This effect is pronounced even at night. Cool nights are important to help people recover from the heat of the day.
Exposure to heat, measured as the number of hot days and tropical nights, is projected to increase across Europe. Cities in southern Europe are most exposed, but these hot days and tropical nights are also projected to increase in western, central and eastern Europe, where people and towns are less accustomed to heat.
Multiple factors influence the exposure of heat, the sensitivity to it and the response capacity (table). The following maps depict some of these factors, and provide some indication of the situation (in green). They need to be interpreted as a whole, together with the other factors still requiring local or qualitative information.