Swiss heatwaves linked to around 600 excess deaths

Around 600 additional deaths were recorded in Switzerland between June and September 2026, as the country endured its hottest summer since measurements began in 1864. Weekly mortality figures from the Federal Statistical Office show a sustained rise that coincided with two periods of extreme heat.

The first wave, which struck at the end of June, caused the sharpest increase. A second, longer episode arrived in early August after a brief break in July. Together, the events pushed summer mortality above expected levels across the country.

The estimate places the human cost of the summer above the Swiss Tropical and Public Health Institute’s recent seasonal average of around 500 heat-related deaths. It remains well below the roughly 1,400 additional deaths recorded during the severe summer of 2003, but the comparison offers little comfort to public health officials facing more frequent hot spells.

The figures also show why heat cannot be treated solely as a weather story. Its effects reach hospitals, care facilities, workplaces and households, particularly when high temperatures persist overnight and limit the body’s ability to recover.

The first heatwave of the summer proved the most lethal, a pattern Martina Ragettli, an epidemiologist at the Swiss Tropical and Public Health Institute, says is common. People have not yet adjusted physiologically or behaviourally to high temperatures when the first major hot spell arrives.

“At the beginning of summer, we are not yet adapted to the heat,” Ragettli told SRF. As the season continues, the body gradually develops greater tolerance. People also learn to change routines, drink more water, limit exertion and seek cooler places.

That adjustment offers only partial protection. The June heatwave arrived early, when households, employers and care providers may not have activated their full heat response plans. High temperatures can worsen cardiovascular and respiratory conditions, increase dehydration and place additional strain on the body.

The timing also matters because Switzerland’s heat exposure varies sharply by setting. Dense urban neighbourhoods retain heat after sunset. Outdoor workers face direct exposure during the day. Residents of care homes and people living alone may need help to recognise symptoms before their condition deteriorates.

The second heatwave exposed a rise in mortality among people under 65, a finding that has drawn particular attention from Swiss researchers. Older people remained the most affected group, as expected, yet the August increase among younger adults showed that vulnerability extends well beyond retirement age.

Ragettli points to a possible change in daily routines. The August heatwave arrived as the holiday period ended and people returned to construction sites, shops, offices and care facilities. Many resumed commuting and outdoor work, with fewer opportunities to stay in cooler environments.

“It was back to everyday life, and people had fewer opportunities to protect themselves from the heat,” Ragettli said. She stressed that this is only one hypothesis. The duration and intensity of the August event may also have contributed, and the available data cannot establish a single cause.

Outdoor workers, delivery staff, commuters and people without access to air conditioning can face prolonged exposure. Employers must manage rest periods, shade, hydration and working hours when forecasts show dangerous temperatures. Individuals with heart or lung conditions also face elevated risks, even if they are far younger than 65.

Heat deaths rarely appear on death certificates as heat deaths. Doctors and registrars usually record the immediate medical cause, such as a heart attack, respiratory failure or circulatory collapse. Extreme temperatures may trigger or accelerate that event without appearing in the official diagnosis.

This makes the Federal Statistical Office’s weekly figures an important warning system, but not a final medical accounting. The data can show that mortality rose unusually during the heatwaves. They cannot, on their own, prove how many deaths were caused by heat or identify the precise pathways.

Swiss TPH researchers will combine mortality records with temperature data to produce a more detailed assessment. Those results are expected in spring 2027. The current evidence points to heat as the main factor behind the rise because no other major event is known to explain the increase.

The wider summer added pressure to the health system and the environment. Switzerland also experienced exceptional drought. Between April 1 and July 31, around one-fifth of monitoring stations recorded their lowest water levels for that period since measurements began. Heat, dry conditions and strained water supplies formed a single season of overlapping risks.

The 2026 figures give Switzerland a clear public health signal before the final analysis arrives in 2027. Around 600 excess deaths in one summer show that heat protection must reach beyond emergency advice for older residents. It must also cover workers, commuters, people with chronic illnesses and residents in buildings that trap heat.

Several Swiss cities have strengthened heat measures, including public warnings, cooling advice and outreach to vulnerable residents. The national picture remains less consistent. Municipalities, cantons, employers, care homes and medical services do not all operate with the same resources or procedures.

The summer’s drought adds a second planning challenge. Lower water levels affect agriculture, ecosystems and local supplies, while dry landscapes can intensify pressure on communities already coping with high temperatures. Switzerland’s Alpine geography does not shield every resident from heat exposure, particularly in cities and lowland regions.

Swiss TPH’s detailed study will clarify the final mortality estimate. The immediate operational lesson is already visible in the weekly data: authorities need earlier alerts, clear workplace protections, stronger support for isolated residents and coordinated action before the first major heatwave arrives.