Swiss heatwaves linked to around 600 excess deaths

Around 600 additional deaths were recorded in Switzerland between June and September 2026, as two extended heatwaves pushed mortality above expected levels. The figures come from weekly monitoring by the Federal Statistical Office and cover the country’s hottest summer since records began in 1864.

The first heatwave, at the end of June, produced the highest increase in deaths. A second spell arrived in early August after a short break in July, extending the pressure on people whose health was already vulnerable to high temperatures.

The figures do not represent deaths certified as caused by heat. Doctors and registrars generally record the immediate medical event, such as a heart attack or circulatory failure. Heat can worsen an existing condition or trigger a fatal event without appearing on the death certificate.

Still, the timing of the mortality increase points to the heat as the most plausible explanation. The Federal Statistical Office can identify an unusual rise in deaths, while a fuller attribution requires mortality figures to be matched with detailed temperature records. Swiss TPH plans to publish that analysis in spring 2027. Until then, the estimate offers a clear measure of the summer’s public health burden.

People over 65 suffered the greatest impact, reflecting the known vulnerability of older adults to extreme heat. Ageing bodies regulate temperature less efficiently, and many older people live with heart, lung or circulatory conditions that heat can aggravate.

The first heatwave also carried a seasonal disadvantage. Martina Ragettli, an epidemiologist at the Swiss Tropical and Public Health Institute, said people are less prepared physiologically when summer begins. “At the beginning of summer, we are not yet adapted to the heat,” she said. As the season continues, the body gradually adjusts and can cope more effectively with high temperatures.

Switzerland’s recent baseline is already high. Swiss TPH estimates that about 500 heat-related deaths occur in an average recent summer. The 2026 estimate of around 600 excess deaths therefore signals a particularly severe season, although the two figures come from different methods and should not be treated as identical measures.

The historical comparison is sharper. Swiss TPH recorded around 1,400 additional deaths in 2003, when a major European heatwave struck Switzerland. That event remains a reference point for assessing the risks of prolonged high temperatures.

Mortality among people under 65 rose noticeably during the second heatwave, an unusual feature of this summer’s data. The increase broadens the health warning beyond retirement homes, hospitals and households caring for older relatives.

Ragettli offered one possible explanation. The August heat arrived after the holiday period, when people returned to construction sites, shops, offices and care facilities. “It was back to everyday life, and people had fewer opportunities to protect themselves from the heat,” she said.

Outdoor workers face direct sun and physical exertion. Commuters and delivery workers can spend long periods in hot vehicles or on exposed platforms. Indoor workplaces may also retain heat when ventilation and cooling are limited. These conditions can reduce the time available to rest, drink water or move into a cooler environment.

Ragettli stressed that these explanations remain hypotheses. The length and intensity of the heatwaves may also have influenced mortality, and the available data cannot establish one definitive cause for the increase among younger adults. The pattern does show how quickly heat risk can reach people who do not usually consider themselves medically vulnerable. Public health warnings need to reach workplaces and transport networks as well as private homes.

Switzerland will receive a more precise account of the summer’s deaths in spring 2027, when Swiss TPH combines mortality records with temperature data. That work should clarify how many deaths can be attributed to heat exposure and how the risk varied across age groups and heatwave periods.

The national picture already extends beyond hospitals and death statistics. Switzerland also faced an 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. Dry rivers, stressed agriculture and overheated urban areas formed part of the same summer environment.

The mortality figures add urgency to preparations for future heat. Swiss cities have introduced measures such as cooling plans, public alerts and shaded spaces, but Switzerland still lacks a consistent nationwide strategy, according to related reporting by Swissinfo. Effective protection requires coordination among cantonal health authorities, municipalities, employers, care facilities and emergency services.

The next assessment will refine the numbers, not erase the warning. Two heatwaves in one summer exposed risks for older residents, outdoor workers and people returning to everyday routines. The country’s public health planning will need to account for heat that lasts longer, arrives earlier and affects more parts of daily life.