All of Germany is currently groaning under the extreme heat. With the current temperatures, cities are turning into real ovens, it is significantly hotter here than in the countryside. But there are clever ways to make our big cities heat-proof for the future.

We are in the middle of a heat wave. There is a local threat of up to 40 degrees. Even in the north, the high temperatures do not stop: On Tuesday, the oppressive heat reached Hamburg with around 30 degrees Celsius. On Wednesday it should be even hotter with up to 38 degrees Celsius in the afternoon. Even the night doesn’t offer any real cooling at the moment, the temperatures don’t fall below 20 degrees in many places.

The new normal? There are more heat waves than before and there will be even more in the future. Experts and scientists agree on that.

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A dangerous situation, because the extreme weather is a great physical strain – especially for the elderly and sick people as well as for small children and pregnant women. From 2018 to 2020, almost 200,000 people across Germany died as a result of the heat. The hot days can become a deadly trap, especially for city dwellers.

Gray asphalt and concrete landscapes with little green space are true heat accumulators. Glass surfaces reflect sunlight. Due to dense development, the air can hardly circulate. Car exhaust fumes also have a negative effect on temperatures. All of this turns big cities into ovens. The so-called “urban heat island effect” ensures that city centers are two to eight degrees hotter than the surrounding areas. There are numerous anti-heat strategies that can make life in big cities much more pleasant.

The most important are summarized here:

There needs to be more greenery in the city! Whether on roofs, facades, streets or sidewalks – green spaces help to lower temperatures in cities. Shady trees also provide plenty of cooling. The cooling capacity of a single tree, for example, is 20 to 30 kilowatts, which is about as much as that of ten air conditioners. This was shown by researchers at the Dutch University of Wageningen.

A recent study commissioned by the Federal Environment Agency (UBA) examined what works best against overheated cities. The researchers tested measures in the cities of Hamburg, Frankfurt am Main, Cologne, Madrid and Tunis. Even if the circumstances were not the same everywhere – some methods proved to be helpful everywhere. In addition to green areas, ponds, fountains and drinking fountains also bring cooling evaporation into urban areas.

Singapore shows what it can look like when cities plant plants on buildings. The tropical city-state has been pursuing this concept for years and is now a global role model for green architecture. Singapore wants to be a “city in a garden”. But there are now also examples of green architecture in Europe. For example in Milan, Italy. The “Bosco Verticale”, two skyscrapers, are covered with 900 trees and 2000 plants. When water evaporates from the plants during hot periods, it has a cooling effect.

The magic word in so-called “sponge cities” is unsealing. Because when cities are paved with asphalt and concrete, rainwater cannot seep into the ground. When the sealing is unsealed, for example, concrete surfaces are broken open – the water can now seep away. The UBA study shows that soil then releases moisture into the air and cools it.

This also explains the term sponge city. Cities absorb water, store it and release it again. So they imitate the structure of sponges. A natural water cycle is created. This not only helps against heat, but also against flooding. Water does not have to be discharged into the sewage system, it can be stored where precipitation falls.

Whether roofs, streets or house facades: In the fight against the heat, light-colored surfaces also prove to be useful. They deflect the sun’s rays and thus store significantly less heat than dark ones. The UBA study shows that surfaces can also be painted in a light color afterwards. You can see that especially in cities like Los Angeles, New York or Athens.

Another helpful measure: shade open spaces in the cities. Sun sails are suitable for this. They prevent seats from heating up too much. The study names Urban-Loritz-Platz in Vienna as a model. Here waiting areas and footpaths are covered with a sail and thus provide shade.

There are numerous measures against overheated cities – but what about the implementation?

There is currently no national heat action plan. In Germany, responsibility lies with the federal states and local authorities. After all – since 2017 there has been a nationwide guideline that is intended to offer cities orientation. The coalition agreement of the traffic light parties states that a strategy for heat prevention should be developed together with the federal states. So far, however, not much has happened.

Also read: Heatwave: These tips will help you keep a cool head

In view of the current heat wave, it is too late for long-term planning. But there are also measures that can help in the short term.

Expert Jörn Birkmann, head of the Institute for Regional Planning and Development Planning (IREUS) at the University of Stuttgart, names three essential instruments in a statement to the Science Media Center: “Early risk communication aimed at vulnerable people and sensitive infrastructures and comprehensive and low-threshold Warning of civil society, secondly, showing cool places as retreats and thirdly, expanding the range of free drinking water in public spaces.”