Trees cool Europe's cities surprisingly well

In Austria and other Central European countries, trees provide townspeople with a lot of cooling in summer, report Swiss researchers. Wherever they are, the temperature on the ground is on average ten degrees Celsius lower than in built-up areas. Treeless green spaces only cool half as much. In the south of Europe, the effects of the trees are much lower, where they only reduce the city heat by around two degrees, they explain in the specialist journal Nature Communications.

A team led by Jonas Schwaab from the Swiss Federal Institute of Technology (ETH) in Zurich compared the surface temperatures measured by satellites in green areas with and without trees and built-up areas in 293 European cities. These included four major Austrian cities: in Vienna, areas with trees are on average eleven degrees Celsius cooler than built-up areas in summer and treeless green areas are 5.5 degrees. In Salzburg trees reduce the temperature by 14 degrees, normal green spaces by eight degrees. In Linz it is 12.5 and 4.5 degrees, in Innsbruck even 15.5 and seven degrees Celsius.

Temperature differences

Accordingly, where trees grow, urban areas are strikingly cooler. “It is important for me to say, however, that these are surface temperatures that are derived from satellite data,” explained Schwaab der WHAT: “The temperature differences in the air, for example at a height of two meters, would be much less great.” Above all, however, the air temperature is important for people’s perception of heat. Therefore, the study results do not directly say how much summer heat the trees actually save people.

In the south of Europe, for example in Cordoba in Spain, the trees do not help so effectively in summer against the much stronger surface heat there. But they cool in such climes in warm spring times as much as possible.

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