More trees are needed to cool down European cities in heatwaves – but they must be planted nearer to homes

A landscape shot of Copenhagen with a line of green trees lining the road
Image credit: Getty Images

An opinion piece written by Dr Simon Hodder, from º£½ÇÉçÇø University's School of Design and Creative Arts, and Dr Thami Croeser, RMIT University, for The Conversation platform.

Heatwaves claimed the lives of tens of thousands of people in Europe’s capital cities this summer, as they experienced record temperatures.

In London,  after fainting in the heat. Meanwhile, the dry weather created  and left .

In Paris temperatures exceeded 40°C in late June and people struggled to carry , and in Madrid,  on the outskirts of the city.

How trees can help

Thami carried out preliminary research on the results of extreme heat on European . The study looked into how many buildings have adequate shade from trees. The results were striking.

In London, Paris and Madrid over 90% of buildings did not have enough shade around them to prevent urban heat island effects. These were among the worst results in cities we studied, but even the best performers had a majority of residents without adequate heat protection – cities like Hamburg (56% unprotected) and Barcelona (70% unprotected).

This builds on past research that shows how major cities around the world – including in Europe – tend to  to create shade close to homes and workplaces. It suggests that that homes should have a view of three trees and be within a 300 m walk of a park.

Early results for my research suggests that huge portions of European cities are exposed to avoidable heat island effects.

How urban heat islands work

On many days during summer 2026 it didn’t get much cooler in the evening. This is because of what is known as the urban heat island effect. Cities , due to  and there are vast amounts of asphalt, clay and concrete. These are almost the perfect materials to soak up and hold heat from all that direct sunshine. Unshaded asphalt can reach  on heatwave days.

Even after sunset, cities stay hot because roads, buildings and footpaths begin to radiate their absorbed heat back at us as they cool. The urban heat island effect can  to ambient temperatures, making a day that is already very hot (perhaps 35°C) even more dangerous in high-asphalt, low shade locations (over 40°C).

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