Jena was the hottest city in Germany last Saturday afternoon.

35.6 degrees, that was hotter than any other June 18 in Jena since weather records began.

The city warned its citizens two days in advance: Please stay in the apartment in the afternoon and do not go out in the sun.

If symptoms such as circulatory problems, vomiting or headaches occur, please consult a doctor.

Draw the curtains and drink a lot.

Joachim Müller-Jung

Editor in the feuilleton, responsible for the "Nature and Science" department.

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The warning is only the beginning.

If it turns out to be a hot summer, for which there is much to be said, then there will be perhaps three dozen more such days in Jena.

Even more so in other cities.

The climate has changed.

It happens slowly but steadily;

it is getting hotter, drier, the groundwater level is sinking.

And when it rains, it is sometimes so heavy that towns, villages and entire regions are flooded.

At least if you haven't prepared for it.

But they can.

It's called climate adaptation.

The term has been known in municipal administrations for about 15 years, but it is only now that many people are realizing what it actually means.

Namely: to prepare for a future that will inevitably come.

And thereby save lives.

Every summer hundreds, sometimes even thousands of people die as a result of the heat.

And with the catastrophe in the Ahr Valley, it suddenly became clear what heavy rain can mean.

In Hamburg: a rainwater playground

However, climate adaptation is a voluntary task for municipalities.

That means they don't have to worry about it.

If something is voluntary, then only those who are particularly affected, who have enough money or enough people in administration, become active.

Otherwise the topic falls behind.

The same is true of climate change adaptation.

The big cities are therefore the pioneers, the small municipalities are usually lagging behind.

In 2007, Hamburg, for example, was the first city in Germany to engage in adaptation.

Especially with the rain, because that is a more urgent task for Hamburg than the heat.

The city has already rebuilt a lot, almost everything out of its own pocket.

The nicest example: A few years ago, a school and several single-family houses were under water.

The area is in a depression where there is also a playground.

It was transformed into a rainwater playground.

It now absorbs the excess water and the children can play with it until it is all gone.

What is not consumed gradually seeps away and forms groundwater.

The area is no longer flooded and the children say: Hopefully the next heavy rain will come soon!

People are also making headway in Jena.

The city is building green climate oases.

The aim is for all citizens to be able to walk to a place in the city within five minutes that relieves the circulation through shade, seating and cooler temperatures.

Garbage trucks with special sensors also drive through the streets.

They come to every corner of the city and measure much more precisely than computer models could calculate where the city is particularly heating up - so that trade can take place there.

Perhaps through a tree that can cool its immediate surroundings down by several degrees Celsius.

Urban gardens are being promoted in Stuttgart, drinking water fountains are being built in Worms, and playgrounds in Karlsruhe are being lowered so that they can be used as urban floodplains.

There are a multitude of ideas and projects.

But that's usually not enough.

Former Federal Environment Minister Svenja Schulze (SPD) set up the Climate Adaptation Center to support local authorities in adapting to climate change.

An employee told the FAS: The municipalities are the "key actors" in the adjustment.

But apart from a few exceptions, they are "often still at the beginning".