The Swiss voice in the world since 1935

Study: trees have major cooling effect even in extreme heat

Trees cool cities better than previously assumed
Even in extreme heat above 39°C, plane trees continue to evaporate large amounts of water, thereby cooling their surroundings, the Swiss study published on Monday found. Keystone-SDA

Plane trees in cities have an important cooling effect even in extreme heat, according to a new study by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). This challenges earlier assumptions that the cooling effect of trees reaches its limits at 30-35° degrees Celsius.

+ Get the most important news from Switzerland in your inbox

Even in extreme heat above 39°C, plane trees continue to evaporate large amounts of water, thereby cooling their surroundings, the study published on Monday found.

This is good news for urban areas. Days with temperatures above 30°C are becoming more frequent. The next important step is to find out how effectively other tree species transpire in extreme heat.

Trees in cities cool their surroundings by evaporating water through their leaves. This process works like sweating: evaporation draws heat from the environment, causing the air temperature to drop.

If leaf temperatures rise above 30-35°C photosynthesis no longer works – the leaf pores close to prevent water loss.

More

‘Not yet fully understood’

In the summer of 2023, the research team from WSL and the Federal Institute of Technology Lausanne (EPFL) measured how plane trees behave under heat stress. The measurements on eight trees in the Geneva suburb of Lancy showed that the water flow in the tree trunks did not decrease even when it was very hot – on the contrary, evaporation actually increased as temperatures rose.

+ When a tree is worth more than air-conditioning

“Obviously, we have not yet fully understood how trees react to extreme conditions,” said study leader Christoph Bachofen. The researchers suspect that, among other things, deep-lying water reserves in the soil helped the plane trees.

The actual cooling effect of urban trees during heatwaves could therefore be significantly underestimated by current predictions using conventional models, the researchers said in the study, which was published in the journal Urban Forestry & Urban Greening.

More

Translated from German with DeepL/sb

We select the most relevant news for an international audience and use automatic translation tools to translate them into English. A journalist then reviews the translation for clarity and accuracy before publication.  

Providing you with automatically translated news gives us the time to write more in-depth articles. The news stories we select have been written and carefully fact-checked by an external editorial team from news agencies such as Bloomberg or Keystone.

If you have any questions about how we work, write to us at english@swissinfo.ch.

Popular Stories

Most Discussed

News

Lakes in Central Switzerland have the best bathing water quality

More

Lakes in Central Switzerland have best water quality for bathing

This content was published on Anyone who swims in a lake in Central Switzerland need have no fear of infection from intestinal bacteria. The water samples taken at 65 bathing sites in 13 lakes all have good to excellent bathing water quality.

Read more: Lakes in Central Switzerland have best water quality for bathing
Historic ring stolen from Basel museum

More

Historic Russian ring stolen from Basel museum

This content was published on Unknown assailants have stolen a historic ring from a Basel museum. The stolen item was a gift from Russian Tsar Alexander I to his host in Basel in 1814.

Read more: Historic Russian ring stolen from Basel museum
Ceasefire drives stock markets higher

More

Ceasefire drives stock markets higher

This content was published on The ceasefire in the Iran-Israel war has visibly eased tensions on the financial markets. The SMI, Switzerland's leading stock market index, has risen above the 12,000 point mark again.

Read more: Ceasefire drives stock markets higher
Swiss stick to tipping in cash

More

Swiss stick to tipping in cash

This content was published on The vast majority of Swiss people tip in restaurants – and preferably in cash. However, there are regional differences.

Read more: Swiss stick to tipping in cash

In compliance with the JTI standards

More: SWI swissinfo.ch certified by the Journalism Trust Initiative

You can find an overview of ongoing debates with our journalists here . Please join us!

If you want to start a conversation about a topic raised in this article or want to report factual errors, email us at english@swissinfo.ch.

SWI swissinfo.ch - a branch of Swiss Broadcasting Corporation SRG SSR

SWI swissinfo.ch - a branch of Swiss Broadcasting Corporation SRG SSR