As the alpine nation endures its latest heatwave, experts from universities in Switzerland have found that temperatures in cities can be up to 10 degrees higher than in the surrounding countryside. Experts have blamed densely packed housing, a lack of wind and trees, and climate change.

Swiss cities trap the heat during hot weather

Over the last week, the residents of Bern, Zurich, Geneva and Lausanne have baked in 34-degree temperatures. While the entire nation has endured significantly higher temperatures than usual, experts noted that those in the city centre were the most affected. 

Moritz Burger, a researcher at the Oeschger Center for Climate Research, explained that "during heat phases like the one we are currently experiencing, the temperatures in the city centre at night are often a good six, in extreme cases even up to 10 degrees above those of less densely built-up areas in the city."

In Bern especially, the old town can be several degrees warmer than outside the city limits. Burger explained that large urban centres create so-called “heat islands,” where air is trapped and heated by city houses and streets, leading to hot days and “tropical nights.” 

Number of heatwaves to increase dramatically in Switzerland

To cope with the increased temperatures, many cities are planting trees and using lighter building materials to absorb the heat. In Lucerne, authorities have started to test a lighter road surface which reflects more sunlight to help cool the city down. 

However, many experts say this won’t be enough, with city authorities in Lucerne predicting the number of “hot days” - days when the temperature rises above 30 degrees Celsius - in the city will increase from two days every 10 years to 22 days a year by 2060. Geo-ecologist Jonas Schwaab from ETH Zurich argued that temporary measures like more trees and lighter asphalt will not do the trick, and that CO2 needs to be reduced to make cities cooler.