Danger levels heat wave
Heat is considered a serious natural hazard, with major impacts on the population, nature and infrastructure. Excessive heat can have an adverse effect on human health. Days with high temperatures represent a potentially major health burden for the population. Recent scientific studies show that heat-related mortality depends not only on daily maximum temperatures (during the day), but also on night time temperatures. In addition, short and intense periods of heat adversely impact human health.
Danger level 1 (no or minor danger)
Despite summerlike temperatures, no particular impacts on the human health or the healthcare system are to be expected. Nevertheless, fragile individuals may begin to feel some discomfort and must therefore protect themselves accordingly.
Danger level 2 (moderate danger)
Effects
- Risk of circulatory complaints
- Physical discomfort
Behaviour
For information on recommended action, see What to do during a heatwave or the Swiss Federal Office for Public Health (BAG) website.
Description of measurement and prognostic values
- Daily mean temperature ≥ 25 °C for one or two consecutive days
Danger level 3 (considerable danger)
Effects
- Risk of circulatory complaints
- Physical discomfort
Behaviour
For information on recommended action, see What to do during a heatwave or the Swiss Federal Office for Public Health (BAG) website.
Description of measurement and prognostic values
- Daily mean temperature ≥ 25 °C for at least three consecutive days
Danger level 4 (high danger)
Effects
- Risk of circulatory complaints
- Physical discomfort
Behaviour
For information on recommended action, see What to do during a heatwave or the Swiss Federal Office for Public Health (BAG) website.
Description of measurement and prognostic values
- Daily mean temperature ≥ 27 °C for at least three consecutive days
Danger level 5 (very high danger)
Heat warnings are only issued for levels 2, 3 and 4.
Notes
Starting on 1st June 2021, MeteoSwiss will issue heat warnings based on the daily mean temperature (Tmean). Tmean is a meteorologically robust index as it does not depend on individual temperature peaks but takes into account the temperature development over the course of the entire day (24 hours). It is calculated as the average of all temperature measurements during one day (from midnight to the following midnight). Using Tmean as heat indicator also allows MeteoSwiss to take into account the night time temperatures. The temperature during the night is particularly important for the human organism. If the nights are too warm, the human body is not able to cool down sufficiently and to recover from daytime heat stress. Our organism can therefore cope less with the heat.
The thresholds and criteria used in the new heat warning system are based on scientific analyses done by the Swiss Tropical and Public Health Institute (Swiss TPH Basel), customized for Switzerland. The study takes into account the effects of mean daily temperature on mortality. According to their study, even one day with high temperatures already leads to an increase in mortality. Taking this into account, from summer 2021, MeteoSwiss has introduced a level 2 warning in the new heat warning concept to warn against short, intense heat periods.
The MeteoSwiss heat warning concept is based on the daily mean temperature and does not take into account other meteorological parameters. In addition to temperature, humidity also has an influence on human well-being, but not on mortality, according to various studies in the Swiss climate.