Europe has just endured a brutal summer heatwave, and the toll was measured in far more than broken records. The World Meteorological Organization reported that large parts of the continent ran 3 to 10°C above the seasonal average through late June.
France logged its hottest day on record on 24 June, a national average of 30.0°C, according to Météo-France. Germany then set a provisional national high of 41.7°C on 28 June, confirmed by the DWD. In Switzerland, Zurich saw the mercury reach 37.1°C, the city's hottest on record, surpassing a high set in August 2003, according to MeteoSwiss.
As the heat pushed eastward, records continued to fall across Central Europe. The Czech Republic logged 41.1°C on 28 June, the first time 41°C has appeared in its official network, according to the CHMI. In Poland, a provisional 40.5°C the same day surpassed a national record that had stood since 1921, the IMGW said.
Behind those numbers were real people. The World Health Organization linked more than 1,300 excess deaths across Europe to the extreme heat since 21 June, while Public Health France recorded around 1,000 excess deaths in the country since 24 June, a rise it said affected all age groups.
Unfortunately, the respite may be short-lived. Forecasting models indicate that another heatwave is already brewing and will hit Western Europe on the second weekend in July. It is a stark reminder that the question is no longer whether extreme heat returns, but when.
Why a Thermometer Is Not Enough
Heat rarely takes its heaviest toll where the thermometer reads highest. Air temperature is only part of the picture: it says nothing about the wind that cools a person, the humidity that prevents sweat from evaporating, or the direct sun that loads heat onto the body.
These factors vary street by street. A shaded, breezy square and a treeless bus stop a few hundred metres apart can pose very different risks on the same afternoon, and a top-floor flat that traps heat overnight can be more dangerous than the daytime peak outside.
This is where Physiological Equivalent Temperature (PET) comes in. PET folds temperature, wind, humidity and solar radiation into a single figure: the equivalent indoor temperature at which a person, sheltered from wind and sun, would feel the same thermal stress as they do outdoors. In short, it measures how hot a place truly feels, which is the number that matters most when heat becomes dangerous.
A 3-Metre View of Urban Heat
This microclimate reality is exactly what the PET map makes visible. Deployed in Zurich, Frankfurt and Gelsenkirchen as part of Urban Maps, a wider platform already present in hundreds of cities worldwide, the map is calculated at a resolution of 3 by 3 metres, fine enough to show the shade cast by a single row of trees or the heat trapped between buildings.
A three-day forecast gives cities enough time to act: to open cooling centres before the temperature peaks, to check on vulnerable residents living alone, and to steer people away from the streets that will affect them most. All of this data is fully digital and also available via API, ready to feed urban planning, public communication or emergency response.
When Information Becomes Relief
Heatwaves are among the weather events with the greatest impact on public health. Unlike storms or floods, their effects are often less apparent, developing gradually over several days. Elderly adults, children and people with pre-existing health conditions are particularly vulnerable, especially during prolonged periods of high temperatures.
Knowing where the danger concentrates changes how a city can respond. A map that shows exactly which blocks turn lethal, and when, lets help reach the right doorstep in time rather than after the fact. That is the difference PET data makes: it turns a heatwave from something a city simply tries to survive into something it can prepare for, and in doing so it can spare lives that a plain temperature reading would miss.
The same mapping can be built for any city that chooses to invest in understanding its own heat. If yours is not yet among them, the people to ask are the ones who shape how it prepares. See what it reveals on the Urban PET Maps. The heat, after all, is not waiting.
