Solothurn Tests Mobile Trees to Combat Urban Heat Islands

The city of Solothurn, Switzerland is using mobile trees, mature trees planted in large steel containers, to mitigate the urban heat island effect on Klosterplatz. City officials installed five maple trees two years ago to test the concept before finalizing plans to transform the square from a parking lot into a public space.

The trees allow the city to experiment with green infrastructure and gather data on effectiveness before making permanent changes. Researchers from the Bern University of Applied Sciences are studying the trees’ cooling impact as part of the “Mobile Urban Green” project, funded by the Swiss federal government.

They are focusing on perceived temperature, how warmth is actually felt considering sun exposure, humidity, and wind, rather than air temperature alone. Preliminary findings show the trees can reduce perceived temperature by 13 to 19 degrees Celsius during hot summer days.

The planters also include 800-liter water tanks and sensors to monitor water levels, reducing maintenance. While more expensive upfront, the system promises long-term cost savings. A decision on the square’s final design, and the trees’ future location, is expected this fall.