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Vulnerabilities - Cold versus heat stress

In Switzerland, both heat- and cold-related mortality will substantially increase this century because of climate change and population development (ageing population). Population development will lead to an increase in cold-related mortality despite the decrease in cold temperature under warmer scenarios. The combination of the progressive warming of the climate and population development will substantially increase and exacerbate the total temperature-related mortality burden in Switzerland. Cold-related mortality will substantially increase from 4069 in the baseline period 1990–2010 to 6558 annual deaths under 2.0 °C and to 5997 under 3.0 °C of global warming. This increase is solely driven by population development (the ageing population). Heat-related mortality is projected to increase from 312 in the baseline period to 1274 annual deaths under 2.0 °C and to 1871 under 3.0 °C of global warming. For this heat-related mortality, both climate change and population development (ageing population) have a similar contribution of around 50% to the projected heat-related mortality trends (35).

Vulnerabilities - Cold stress

For most countries, it is hard to say whether an increase of the number of heat stress victims is compensated by a decrease of the number of cold stress victims. Generally, In Europe the mortality in cold winters is higher in countries with relative mild winters than in countries with cold winters. In Switzerland 400-1000 people die from flue every winter (2).

Most European countries have between 5 and 30 % higher death rates in winter than in summer. Winter‑related mortality in many European populations has declined since the 1950s (16). Cold days, cold nights and frost days have become rarer, but explain only a small part of this reduction: improved home heating, better general health and improved prevention and treatment of winter infections have played a more significant role (17).

Vulnerabilities - Heat stress

Heat stress is determined by air temperature and humidity. Regional climate model (RCM) simulations of changes in daily maximum air temperature and daily mean specific humidity show a continuous increase of summer mean and maximum heat stress in Switzerland during the 21st century under a moderate (RCP 4.5) and high (RCP 8.5) scenario of climate change. By the end of the 21st century, high heat stress conditions may occur 3–5 times more often under the high-end scenario of climate change – with 4–6 events per year – than under a low-end scenario (RCP 2.6) scenario of climate change. Heat stress spells are also projected to last longer (31).

The summer of 2003

The increase in intensity of heat waves in combination with high tropospheric ozone concentrations represents the greatest direct risk that climate change poses to people’s health in Switzerland. During the heat wave of 2003 almost 1000 deaths were attributed to the extraordinary heat (1). For the whole of summer 2003, the number of heat related deaths in Western Europe is believed to amount to over 44,000 (15,18). During 4-15 August 2003, the mortality of men and women over 80 years old was 21 and 19% higher, respectively, than the long-term average in this period of the year (2).

The experience of 2003 shows that those most likely to die of the heat are the old, the chronically ill, and the isolated. Both northern and southern Europe are at risk (18).

In Switzerland, June 2003 was the hottest month ever recorded in 250 years of archives and a temperature record of 41.5°C was reached on August 11. With temperatures exceeding the average by +5.4°C in Geneva, the prevailing conditions corresponded to a usual summer in Rio de Janeiro! … With a death toll estimated to exceed 30,000, the heat wave of 2003 is one of the ten deadliest natural disasters in Europe for the last 100 years and the worst in the last 50 years (14). In Switzerland, the 2003 heat have caused an estimated 7% increase in all-cause mortality (30).

It has been shown that there is an optimum temperature range for which the mortality is at its lowest, and that this range is different for different parts of Europe:14.3-17.3°C in the north of Finland, 19.3-22.3°C in London and 22.7-25.7°C in Athens, for instance (2).

After a heat wave the mortality drops below the average. This phenomenon is called the „harvesting effect“: a part of the heat victims refers to people who would have died a few days later anyway, without a heat wave (3). Still, a part of the victims are people that would not have died otherwise: thus, a heat wave results in a higher mortality over a long period of time (4). There are indications that more people die during a heat wave at the beginning than at the end of the summer, when people are more used to the heat (5).

It is expected that the mortality in the summer will increase substantially because of climate change (6). Not only high temperatures during the day but also during the night are important. Especially in cities the nights will cool less during the summers because of the urban heat island effect. Probably, in the future more people will live in big cities. Thus, more people are subject to higher temperatures (2).

The summer of 2022

The summer of 2022 was Europe’s hottest since 2003. A study for Switzerland shows that 60% of the people that died from heat that summer would not have died in the absence of global warming.

Research has shown that nearly 1% of the global population dies because of heat (33). One out of three of these heat-related mortalities can be attributed to human-induced climate change (34). A recent study focused on the observed mortality due to heat in Switzerland during the summer of 2022 and quantified the contribution of human-induced climate change to this extreme event. They concluded that 60% of the people that died from heat that summer in Switzerland would not have died in the absence of global warming (32).

The summer of 2022 in Western and Central Europe was characterized by a cascade of heatwaves. Temperatures reached extremely high values, partly amplified because of the drought that reduced the cooling effect of evaporation. The number of people that died during these heatwaves in Switzerland was much higher than in the same period in previous years. 3.5% of all-cause deaths between June and August 2022 were attributed to heat, and 60% of this heat-related mortality was due to anthropogenic climate change (32).

For the period 1990-2017, thus not including the COVID pandemic, researchers quantified the relationship between summer heat and mortality. They quantified the summer heat that would have occurred in Switzerland in 2022 in the absence of global warming. Then they used the heat-mortality relationship over the 1990-2017 period to quantify the hypothetical number of heat-related deaths in a summer without climate change, compared this number with the observed heat-related mortality, and quantified the impact of climate change as the difference between these two numbers (32).

In this study, a distinction was made between people younger and older than 65. Remarkably, the percentage of deaths attributed to heat was the same for both age groups, about 3.5%. However, nearly 90% of the estimated heat-related mortality happened in the age group of people over 65, simply because overall mortality is much higher in this age group.

In the absence of climate change, the heat-related burden would have amounted to 1.4% of all-cause mortality. Thus, 2.1% of the all-cause mortality in the summer of 2022 can be attributed to climate change. This corresponds to 60% of the observed heat-related mortality (32).

Urban heat islands

In cities, the heat load is larger than in the surrounding area due to the larger proportion of sealed surfaces, less numerous green areas, waste heat from buildings, industry and traffic, and poor air circulation. With climate change, the problem of urban heat islands will increase (19).

The urban heat island (UHI) of the 10 most populous cities in Switzerland has been quantified for the 6 year period 2016-2022. The results show that the UHI is of considerable magnitude, in spite of the relatively small size of Swiss cities. The average UHI during this 6 years period is 1.36°C for Zurich and less then 1°C for all other cities. All 10 cities have days with maximum UHI exceeding 3°C. The UHI is highest during the night (36).

Vulnerabilities - Tick-borne diseases

In the case of diseases transmitted by ticks, global warming may affect the distribution of the vectors, the infection rate and the season in which the vectors are active (1). The number of Lyme-Borreliose infections is increasing. This is not only due to climatic factors but also due to changes in recreational behavior (8).

Worldwide more than 800 different ticks are known. In Switzerland Ixodes ricinus is the most important one; it can spread several illnesses, especially a bacteria (Borrelia burgdorferi) and a virus (Zeckenenzephalitis-Virus). In Switzerland 5-30% of the ticks are infected by Borrelia burgdorferi; about 3,000 people get Lyme-Borreliose each year. Only 1% of the ticks in some nature reserves are infected by the virus; people are therefore seldom infected by this virus (2).

Vulnerabilities - Vector-borne diseases

It is still highly uncertain what future developments are to be expected with respect to the occurrence of vector-borne diseases. In Switzerland, the dissemination of malaria or dengue fever is quite unlikely. However, some vector-borne diseases, such as West Nile virus, occur more often. In a warmer climate, some parasitic vectors may change their host or new vectors may appear (1). The number of vector-borne diseases (for humans and animals) in Switzerland is increasing; this is due to the import of diseases from global travelling (2).

Since 1990, malaria has been observed in parts of Europe (southern Europe, parts of the former Soviet Union, Turkey) (9). These outbursts are probably not related to climate change, but are due to a deterioration of socio-economic and health circumstances, global tourism and an increasing resistance of the mosquitoes against vaccines. Malaria infections in Western Europe will be restricted to relatively few people (2).

Vulnerabilities - Water-borne diseases

Climate change may affect the number of water-borne diseases through more intense rainfall, floods, and higher temperatures (10). In industrialized countries, epidemics after floods have not been observed (11). Higher temperatures have an effect on the number of illnesses through certain types of algae (such as Cyanobakterien).In general, drinking water quality is not expected to suffer so much from climate change in Europe as to have an effect on the spread of water-borne diseases (2).

Vulnerabilities - Air quality

High summer temperatures affect air quality through an increase of ozone concentration and smog. Both the heat and substances like NO2 and fine particles can strengthen the impact of ozone. From research it is shown that ozone is a serious health risk for the Swiss population (7). Ozone may lead to infections of the bronchial tubes, reduce the lung function and result in premature death (2).

Climate change may both increase the concentration of pollen and the length of the pollen season, and thus increase the impact on allergies. It is unlike though, that the observed increase of the number of asthma and hay fever patients over the last decades is related to change in pollen concentrations (2).

Vulnerabilities - Floods

Floods may result in death by drowning, injuries and psychological traumas. The latter may last for months or even years after a flood (12). In Poland 50 suicides are related to the 1997 flood (13). In between 1980 and 1999 1.3 deaths and 5.7 injured casualties have been observed in Western Europe per 10,000,000 citizens per year (12). Floods may also lead to the spread of pollutants.

Vulnerabilities - Food poisoning

As a result of climate change, the danger of food poisoning due to spoilt food and of diseases spread by food (e.g. salmonella) will increase. This risk is particularly high during heat waves and primarily affects private households, where knowledge about the proper handling of perishable food is limited (19).

Adaptation strategies - Switzerland

The Swiss population needs to be better informed about heat-related risks. The experience of 2003 can be used as a basis. A heat warning system along with a monitoring of temperature and mortality should be introduced. Information should be given how to protect against ultraviolet radiation and substances such as ozone. A monitoring of the number of tick-borne and vector-borne diseases in relation to climate variability should be introduced (2).

Urban heat islands

In Switzerland, the increased heat load in cities has been neglected so far in urban development. This aspect needs to be considered in spatial planning in order to prevent the heat load resulting from climate change from increasing further for urban dwellers. Thus, for instance, greening and shading of pavements and pedestrian zones can reduce the heat load (19).

Adaptation strategies - General - Heatwaves

The outcomes from the two European heat waves of 2003 and 2006 have been summarized by the IPCC (20) and are summarized below. They include public health approaches to reducing exposure, assessing heat mortality, communication and education, and adapting the urban infrastructure.

1. Public health approaches to reducing exposure

A common public health approach to reducing exposure is the Heat Warning System (HWS) or Heat Action Response System. The four components of the latter include an alert protocol, community response plan, communication plan, and evaluation plan (21). The HWS is represented by the multiple dimensions of the EuroHeat plan, such as a lead agency to coordinate the alert, an alert system, an information outreach plan, long-term infrastructural planning, and preparedness actions for the health care system (22).

The European Network of Meteorological Services has created Meteoalarm as a way to coordinate warnings and to differentiate them across regions (23). There are a range of approaches used to trigger alerts and a range of response measures implemented once an alert has been triggered. In some cases, departments of emergency management lead the endeavor, while in others public health-related agencies are most responsible (24).

2. Assessing heat mortality

Assessing excess mortality is the most widely used means of assessing the health impact of heat-related extreme events.

3. Communication and education

One particularly difficult aspect of heat preparedness is communicating risk. In many locations populations are unaware of their risk and heat wave warning systems go largely unheeded (25). Some evidence has even shown that top-down educational messages do not result in appropriate resultant actions (26).

More generally, research shows that communication about heat preparedness centered on engaging with communities results in increased awareness compared with top-down messages (27).

4. Adapting the urban infrastructure

Several types of infrastructural measures can be taken to prevent negative outcomes of heat-related extreme events. Models suggest that significant reductions in heat-related illness would result from land use modifications that increase albedo, proportion of vegetative cover, thermal conductivity, and emissivity in urban areas (28). Reducing energy consumption in buildings can improve resilience, since localized systems are less dependent on vulnerable energy infrastructure. In addition, by better insulating residential dwellings, people would suffer less effect from heat hazards. Financial incentives have been tested in some countries as a means to increase energy efficiency by supporting those who are insulating their homes. Urban greening can also reduce temperatures, protecting local populations and reducing energy demands (29).


The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Switzerland.

  1. Federal Office for the Environment FOEN (Ed.)  (2009)
  2. Thommen Dombois and Braun-Fahrländer (2004)
  3. Schwartz (2000a,b); Zeger Dominici et al. (1999), in: Thommen Dombois and Braun-Fahrländer (2004)
  4. Koppe Jendritzky (2004); Koppe et al. (2003), in: Thommen Dombois and Braun-Fahrländer (2004)
  5. Kyselý Huth (2004), in: Thommen Dombois and Braun-Fahrländer (2004)
  6. IPCC (2001); Semenza et al. (1999, 1996), in: Thommen Dombois and Braun-Fahrländer (2004)
  7. Gryparis et al. (2004); Samet et al. (2000); Katsouyanni et al. (1997), in: Thommen Dombois and Braun-Fahrländer (2004)
  8. Randolph (2002); Randolph (2001b); Randolph Rogers (2000), in: Thommen Dombois and Braun-Fahrländer (2004)
  9. Epstein (2000), in: Thommen Dombois and Braun-Fahrländer (2004)
  10. Hunter (2003), in: Thommen Dombois and Braun-Fahrländer (2004)
  11. Greenough et al. (2001), in: Thommen Dombois and Braun-Fahrländer (2004)
  12. Hajat et al. (2003), in: Thommen Dombois and Braun-Fahrländer (2004)
  13. Kovats et al. (1999), in: Thommen Dombois and Braun-Fahrländer (2004)
  14. UNEP (2004)
  15. Swedish Government Official Reports (2007)
  16. Kunst et al. (1991); Lerchl (1998); Carson et al. (2006), in: EEA, JRC and WHO (2008)
  17. Carson et al. (2006), in: EEA, JRC and WHO (2008)
  18. Kosatsky (2005)
  19. OcCC/ProClim- (2007)
  20. IPCC (2012)
  21. Health Canada (2010), in: IPCC (2012)
  22. WHO (2007), in: IPCC (2012)
  23. Bartzokas et al. (2010), in: IPCC (2012)
  24. McCormick (2010b), in: IPCC (2012)
  25. Luber and McGeehin (2008), in: IPCC (2012)
  26. Semenza et al. (2008)), in: IPCC (2012)
  27. Smoyer-Tomic and Rainham (2001), in: IPCC (2012)
  28. Yip et al. (2008); Silva et al. (2010), both in: IPCC (2012)
  29. Akbari et al. (2001), in: IPCC (2012)
  30. Ragettli et al. (2017)
  31. Casanueva et al. (2023)
  32. Vicedo-Cabrera et al. (2023)
  33. Zhao et al. (2021), in: Vicedo-Cabrera et al. (2023)
  34. Vicedo-Cabrera et al. (2021), in: Vicedo-Cabrera et al. (2023)
  35. De Schrijver et al. (2023)
  36. Canton and Dipankar (2024)

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