High temperatures and heatwaves pose a threat to human health. Heat can lead to exhaustion and heat stroke. It can also exacerbate existing conditions such cardiovascular and respiratory diseases, kidney problems or mental health issues. According to the European Environment Agency EEA, heat is the greatest direct climate-related threat to human health in Europe.
The «heat-related deaths» indicator estimates the number of deaths statistically attributable to heat stress in Switzerland between May and September. The indicator can be used to track the long-term impacts of climate change on human health and determine the need for adaptation measures.
Between 2000 and 2022, estimated numbers of heat-related deaths peaked in the hottest summer on record (2003) and the third hottest summer on record (2015). In the record summer of 2003, a total of 1,402 deaths (95% confidence interval (CI): 1,157-1,658) were attributable to heat. This corresponds to 5.6% of total mortality between May and September. In the summer of 2015, an estimated 747 (CI 95%: 544-935) or 2.9% were heat-related. Over-75s are generally the worst affected, and a higher proportion of women die from heat-related causes than men.
The indicator helps to assess the impact of different mean daily temperatures by showing the number of heat-related deaths in three temperature ranges based on the MeteoSwiss heat warning thresholds. The most heat-related deaths occur in periods with moderately hot (above optimal seasonal temperatures and below 25°C) and hot mean daily temperatures (at least 25°C but below 27°C). In moderately hot periods, fewer people die from heat-related causes than during periods of very hot weather (27°C and above), but moderately hot periods are also much more common.
Heat-related mortality during hot spells and heatwaves has fallen slightly over time. For example, although temperatures were high, the estimated figures for the second hottest summer (2022) and the fourth to sixth hottest summers (2017, 2018 and 2019) are lower than would be expected based on the 2003 and 2015 figures. This suggests that society has adapted to some extent to the stress of increased heat levels.
In Switzerland, far more people die from heat-related causes than, for example, traffic accidents. In 2022, 241 people were killed in traffic accidents. In 2022, 474 deaths were recorded as «heat-related». Owing to the high number of heat related deaths, progress on this key indicator has been deemed «poor». With climate change, heat waves and hot spells are becoming more frequent and intense. Therefore, measures to protect human health are becoming increasingly important. The evolution, therefore, is described as «unsatisfactory».
More information on heat and human health from the National Centre for Climate Services: Human health (admin.ch)
There is currently no uniform international reporting on heat-related mortality, so it is not possible to make comparisons at international level on the basis of this indicator.
Since 2023, the heat-related death rate in Switzerland have been estimated based on the number of deaths attributable to heat-related causes. Data on the measured mean daily temperatures is associated with exposure and outcome data to show the correlation between temperature and observed mortality. Unlike the current mortality statistics of the FSO and the the analyses of excess mortality in especially hot summers, the «heat-related deaths» indicator incorporates the temperature measures by MeteoSchweiz. This better takes into account the impact of moderately hot and warmer periods. The method can also attribute deaths to heat-related causes if several extraordinary events simultaneously exert an influence on mortality in one summer. The indicator thus complements the FSO's Mortality statistics, which compares weekly numbers of deaths against expected mortality.
Explanation of daily mean temperatures: A daily mean temperature of 25°C is reached, for example, when the daily minimum temperature is 21°C and the maximum is 29°C, or when the daily minimum is 18°C and the maximum is 32°C. Very hot conditions of more than 27°C daily mean are reached, for example, with a combination of 15.9°C daily minimum and 36.5°C daily maximum or 22.2°C daily minimum and 32.3°C daily maximum.