Belgium’s June heatwave caused 1,747 more deaths than expected between 18 June and 1 July, a 47.8% rise in mortality, according to data published on Wednesday by the federal research institute for public health, Sciensano.
The south of the country was hit hardest. Excess mortality reached 76% in Wallonia, compared with 31.4% in Flanders and 60.9% in Brussels.
Older people were not the only group affected. Among people aged 15 to 64, excess mortality was 61.3%.
The deadliest period was the weekend of 27 - 28 June. There were 641 deaths on that Saturday, equivalent to an excess mortality rate of 146.5%, and 632 (+143.1%) on Sunday.
By the end of the month, when temperatures had eased slightly, daily deaths had fallen back to about 260.
Some excess mortality is expected during heatwaves or cold spells, but the June 2026 episode was exceptional in scale, Sciensano noted. It was the highest excess mortality recorded during a heatwave across the entire period analysed since 2000, both in absolute terms, with 1,747 additional deaths, and in relative terms, at 47.8%.
During the previous major heatwave, in August 2020, excess mortality stood at 37.5%, with 557 additional deaths.
Sciensano said the exceptional impact of the June heatwave was caused by a combination of three factors: its duration, the intensity of the temperatures, and ozone concentrations.
For each of these factors, the episode reached particularly high levels, the agency said.
