Belgium’s third heatwave of summer 2026 ends, but the health toll remains unclear

Belgium’s third heatwave of summer 2026 ended on Monday, 17 August, after the temperature at the Royal Meteorological Institute’s reference station in Uccle dropped below the level needed to keep the episode running, La Libre Belgique and La Dernière Heure reported. The change brings relief to households, care homes, outdoor workers and densely built neighbourhoods in Brussels and other cities, although it does not by itself end the federal season of vigilance for heat and ozone.

For people in Belgium, the immediate distinction matters. The Royal Meteorological Institute, known as the IRM, applies a climatological definition: Uccle must record maximum temperatures of at least 25°C for five consecutive days, including at least three days reaching 30°C. Once that sequence is broken, the meteorological heatwave ends. Public-health precautions operate under separate criteria, however, and Belgium’s vigilance period for strong heat and ozone continues annually until 30 September under the federal plan.

That means cooler weather is not the same as a clean bill of health. Sciensano’s mortality monitoring has repeatedly found that deaths can rise during severe heat and in the following days, particularly among older people. The institute stresses that its all-cause mortality figures reveal associations rather than proving that heat caused every additional death. No consolidated mortality estimate for this third 2026 heatwave was available on Monday, and federal Health Minister Frank Vandenbroucke’s department had not announced a specific assessment of the episode in the material reviewed for this article.

The unanswered question is especially important after the first official heatwave of the summer. IRM records show that the Uccle episode from 17 to 28 June lasted 12 days, included seven days of at least 30°C and peaked at 35.5°C. Preliminary Risk Management Group data subsequently reported by Brussels broadcaster BX1 indicated 1,222 more deaths than expected between 18 and 29 June, an excess of 39%. Those preliminary figures described deaths from all causes and should not be read as a confirmed heat-attributable toll.

The June episode also showed why warm nights can be as consequential as daytime peaks. According to the IRM, the highest minimum temperature during that heatwave reached 24.1°C, a record for a Belgian heatwave, while the average minimum equalled the previous record. Little overnight cooling deprives bodies and buildings of recovery time, increasing pressure on older residents, people with chronic illnesses and those living in poorly insulated or top-floor accommodation.

There are two legitimate ways to frame Monday’s development. The meteorological view, represented by the IRM, treats the fall below the defined threshold as the formal end of a measurable event. The public-health view, represented by Sciensano and the federal heat-and-ozone plan, treats exposure and its delayed effects as a continuing risk requiring surveillance. These are complementary perspectives rather than a dispute: one provides a consistent climate benchmark, while the other guides protection of vulnerable people.

The broader European picture makes the repetition more significant than an isolated spell of summer weather. The EU’s Copernicus Climate Change Service reported that western Europe had already experienced an unusually early and intense heatwave between 21 and 30 May. Copernicus says Europe has warmed by about 0.56°C per decade since the mid-1990s, more than twice the global average, and expects heatwaves to become more frequent, intense and extended beyond the traditional summer season.

Belgium therefore sits inside a continental pattern, even though national heatwave counts depend on measurements at Uccle and cannot be directly compared with alerts issued under different rules in France or elsewhere. Brussels also has two distinct roles: it is a dense city exposed to urban heat, and it hosts EU institutions overseeing Copernicus data and European climate policy. The end of this episode offers short-term respite in the city; it does not settle the longer argument over adaptation, housing quality, workplace protection and emissions reduction.

Attention now turns to the next forecasts, ozone measurements and delayed mortality data. The federal vigilance period remains active, so residents should continue checking IRM and regional health guidance if temperatures climb again. What remains unknown is whether another qualifying heatwave will develop before autumn and how large the cumulative health impact of Belgium’s exceptionally repetitive summer will prove to be.