More trees are needed to cool down European cities in heat waves—but they must be planted near homes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Heat waves claimed the lives of tens of thousands of people in Europe's capital cities this summer as they experienced record temperatures. In London, emergency wards filled with elderly patients injured after fainting in the heat.

Meanwhile, dry weather caused subsidence and left homes with cracks. In Paris, temperatures exceeded 40°C (104°F) in late June, and people struggled to carry on with their lives. In Madrid, heat waves burned thousands of hectares on the outskirts of the city.

Thami carried out preliminary research on the effects of extreme heat on European cities this summer. The study examined how many buildings have adequate shade from trees. The results were striking.

In London, Paris and Madrid, more than 90% of buildings did not have enough shade around them to prevent urban heat island effects. These were among the worst results in the cities studied, but even the best performers had a majority of residents without adequate heat protection—cities such as Hamburg (56% unprotected) and Barcelona (70% unprotected). This builds on past research showing how major cities around the world—including in Europe—tend to struggle to reach useful levels of tree canopies to create shade close to homes and workplaces.

It suggests that homes should have a view of three trees and be within a 300 m (984-foot) walk of a park. Early results from the research suggest that huge portions of European cities are exposed to avoidable heat island effects. On many days during summer 2026, it did not get much cooler in the evening.

This is because of what is known as the urban heat island effect. Cities typically lack shade, due to high rates of tree removal, sparse planting, and poor tree health, and there are vast amounts of asphalt, clay and concrete. These are nearly perfect materials for soaking up and holding heat from direct sunshine.