June 27: Second Deadliest Day of Century in Belgium Heatwave

June 27, 2026, was the second deadliest day of the 21st century in Belgium, with approximately 650 deaths recorded in a single day, according to provisional data published by Statbel, the Belgian national statistical office. Only the peak of the first COVID-19 wave in April 2020, which saw 675 deaths on April 10, surpassed this toll. The following day, June 28, recorded approximately 640 deaths, making it the third deadliest day of the century.

Context

The deaths occurred during an unprecedented 12-day heatwave that swept across Belgium from June 17 to June 28, with temperatures approaching 40°C at its peak. The official heatwave was recorded at the Uccle meteorological station, operated by the Royal Meteorological Institute (IRM). The data, based on a National Register extract from July 18, 2026, shows that in total, 9,741 people died in Belgium during June 2026 — 5,351 in Flanders, 3,582 in Wallonia, and 808 in the Brussels-Capital Region.

What made this heatwave particularly dangerous was not just the daytime highs but the exceptionally high night-time temperatures. For 10 consecutive nights, minimum temperatures remained above 18°C, preventing the body from recovering from daytime heat exposure. This lack of overnight relief is a known risk factor for heat-related mortality, as it places sustained stress on the cardiovascular and respiratory systems.

Key Developments

According to RTBF, the figures released on July 23 confirm that the heatwave’s human toll was catastrophic. The Belgian Institute of Public Health, Sciensano, reported that excess mortality during the heatwave period (June 18 – July 3) reached 48% — the highest ever recorded for a heatwave since monitoring began in 2000. This translates to approximately 2,000 excess deaths, a figure that was revised upward from an initial estimate of 1,747.

“It is the combination of three factors that explains the exceptional nature of this heatwave episode: its duration, the intensity of temperatures, and ozone concentrations,” Sciensano stated, as reported by Brussels Today. Ozone concentrations exceeded EU information thresholds on June 25, 26, and 27, while high PM2.5 particulate levels were observed in Flanders and Brussels on June 25. The combination of extreme heat and poor air quality created a compounded health hazard.

Regional Disparities

The impact varied dramatically across Belgium. Wallonia suffered the highest toll with 77% excess mortality (1,059 excess deaths), followed by Brussels at 63% (188 excess deaths), and Flanders at 31% (768 excess deaths), as reported by DHnet.

Notably, the heatwave affected more than just the elderly. Excess mortality among working-age adults (15–64) reached 61.3%, challenging the common assumption that extreme heat primarily threatens older populations. This suggests that occupational exposure, housing quality, and access to cooling played significant roles in determining who was most at risk.

Analysis

The June 2026 heatwave far exceeded previous major events. The August 2020 heatwave caused 37.5% excess mortality (1,557 excess deaths) — significantly less than the current figures. The only comparable mortality levels in recent Belgian history were during the first COVID-19 wave in April 2020, when the healthcare system was overwhelmed and the country was under strict lockdown.

Sciensano noted that a delayed mortality effect contributed to the high toll. “This is not unusual. Other countries also observe a delayed effect: people can die from the effects of a heatwave even after it has passed,” the institute explained. The institute extended its reference period by two days because mortality remained significantly elevated on the fourth and fifth days following the heatwave. The data also reflects that France experienced 5,764 excess deaths during the same late-June heatwave, indicating a broader European public health crisis consistent with climate change projections for Western Europe.

The stark regional disparities have prompted urgent policy questions. Why was Wallonia hit so much harder than Flanders? Possible explanations include differences in housing quality — older buildings with less effective cooling — as well as population age structure, access to green spaces, and socioeconomic factors. The PS party has proposed a “massive plan” including heatwave unemployment benefits, drinking water points, and free public transport during extreme heat events. As another heatwave was forecast for late July 2026, the need for adaptive measures has become increasingly urgent.

What’s Next

All figures remain provisional, based on a National Register extract from July 18, 2026. Statbel emphasizes that these are statistical measurements and do not alone establish causality with any specific phenomenon. Final consolidated mortality statistics are not expected until mid-2027, and the figures could be revised upward or downward. With climate projections indicating more frequent and intense heatwaves, Belgium faces pressing questions about heatwave preparedness, infrastructure resilience, and the protection of vulnerable populations across all regions. The data from June 2026 serves as a stark warning: extreme heat is no longer a future threat but a present-day public health emergency.