Trees and grass cool urban heat islands

Swiss researchers are analysing the problem of increasing heat in cities. The Federal Laboratories for Materials Science and Technology has developed initial model calculations for areas such as the Münsterhof square in Zurich.

A simulation program developed by the Federal Laboratories for Materials Science and Technology (Empa) can make detailed predictions about which pavements and types of vegetation could help cool urban heat islands.

Such calculations could minimise the increasing heat stress caused by climate change, according to a statement. The researchers simulated their model on the Münsterhof in Zurich.

In summer, concrete and facades heat up considerably. The climate simulation developed by scientists from the Laboratory of Multiscale Studies in Building Physics at Empa and the Chair of Building Physics at the Federal Institute of Technology in Zurich (ETH) shows that soil and grass on the Münsterhof would significantly reduce temperatures.

The ground would cool down more at night and store less heat during the day. Even if only a quarter of the paved area at Münsterhof were re­placed by a porous floor covering that could be watered, the “oven” would be deactivated in summer, according to the statement.

The researchers also simulated the effect of four narrow standing trees on the northeast side of the square. “The shade of the trees and at the same time their transpiration cooling would greatly reduce the heat stress,” said Aytaç Kubilay, an ETH and Empa expert in heat sources. That the trees can change the wind-flow field would also help cool the square.

There are plans to further refine the simulation in order to enable city planners to make detailed predictions on how heat islands can be tackled.

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