Heat: People will suffer the most in these German cities

Climate change is noticeable: More than twelve million Germans are exposed to extreme heat stress in their homes during the summer. This is shown by new data from the German Environmental Aid (DUH), presented on Thursday. As in the previous year, the DUH conducted a nationwide "heat check" and evaluated data from 190 German cities with more than 50,000 residents.

The heat stress is highest in Mannheim, and lowest in Hattingen. Calculating heat stress isn't just about how high the temperatures are in summer. Urban design is also taken into account, which can make residents more or less able to tolerate the summer heat. For example, many built-up areas cause urban areas to heat up particularly quickly. While green spaces and trees provide pleasant cooling.

Therefore, in addition to summer temperatures, the German Environmental Aid (DGU) measured the extent of sealed surfaces in cities, using satellite data from the EU's Copernicus Earth observation program and AI models. Aerial photographs were also used to determine the height of vegetation in the respective cities. This yielded the "green volume" that contributes to cooling. This year, population density was also taken into account, as heat is particularly stressful in densely populated areas.

Data on summer temperatures, the proportion of sealed areas and green spaces, and the population density of the cities studied were compared with national averages for the survey. Points were awarded depending on whether the corresponding values ​​were above or below the average – and by how much. Areas with high temperatures, high levels of sealed areas, and little green space received more points than cooler, greener, and less densely populated areas. Based on all of this data, the DUH ultimately calculated a heat impact index for all 190 cities studied and published it in tabular form.

Mannheim has a heat stress index of 18.61, the highest in Germany. The table also includes a column titled "Resident distribution by heat stress level." This shows that in Mannheim, approximately 88 percent of residents are affected by severe heat stress, and around 12 percent by moderate heat stress. Ludwigshafen and Worms also have particularly high levels of heat stress.

Hattingen in North Rhine-Westphalia, on the other hand, has the lowest heat stress index in all of Germany, with a value of just 11.99. Only around eight percent of the population there is exposed to severe heat stress at their place of residence, around 69 percent is moderately exposed, and around 23 percent is low.

Of the other cities with low levels of pollution, many are, as expected, located in the north, such as Kiel, Wilhelmshaven, and Flensburg. Summer temperatures there are comparatively moderate. But even there, action is needed, according to a press release from the DUH. Some of these cities have sealed surfaces of over 45 percent and urgently need to invest in green spaces in the coming years. Because as the climate crisis progresses, the north will soon be even more severely affected by heat.

A total of 24 cities received a "red card," meaning they were above average in heat stress. 82 were issued a "yellow card" for average heat stress, and 84 received a "green card" for below-average heat stress.

"Our heat check is an alarm signal and should serve as a wake-up call for local, state, and federal policymakers," said Barbara Metz, Federal Director of the DUH, at the presentation of the heat check. "It clearly shows where the need for action to create green spaces is most urgent. From now on, greening cities and preserving trees must be given the same priority as housing construction and any other infrastructure." Of the 34 million people in the cities surveyed, 32 million are affected by moderate to extreme heat stress. Around 3,000 people die in Germany every year as a result of extreme heat.

The DUH is calling for a mandatory minimum green space on every property, building, and in public spaces. Municipalities also need the necessary financial support to green their cities, according to Metz. The DUH is calling on citizens to directly request their city to provide more heat protection. This can be done online at: www.duh.de/hitze-check.