Trees play a crucial role in shaping surface temperatures in our cities. New research conducted in Stockholm vividly demonstrates this impact. The study, led by Ulla Mörtberg, Professor of Energy Systems Analysis and Environmental Assessment, and Elina Merdymshaeva, PhD student and geographical analyst, spanned three months during the summers of 2022 and 2024, covering various parts of Stockholm.
Measuring urban surface temperatures isn’t new; typically, satellites or drones are used for such assessments. However, to get a more precise picture of Stockholm’s surface temperatures, the researchers took an innovative approach. They mounted IR camera scanners onto city vehicles like garbage trucks, three-wheeled electric mopeds, and e-bikes. This allowed them to measure the external temperature of building facades, street spaces, and areas around existing greenery. Measurements were taken in locations such as Hammarby Sjöstad, Södermalm, and around Norr Mälarstrand in Stockholm.
“We were able to pinpoint which facades are warmer and which parts of a street are more exposed to heat,” explains Elina Merdymshaeva.
In their measurements, the researchers focused on observation surfaces that remain stable over time, also considering the volume and area of buildings. They harnessed machine learning to uncover connections and combinations of variables, and Stockholm City’s tree data proved to be an invaluable asset. The researchers examined the landscape, individual city blocks, and a micro-scale, enabling them to uncover more details than previously possible.
“What’s new is that we can link surface temperatures to how the sun hits building facades and how trees interact with that, on a micro-scale but across the entire urban landscape. There’s a clear relationship between these two factors. Trees are significant for shading and cooling,” says Ulla Mörtberg.
How This Research Can Shape Greener Cities
These measurements are intended to directly support the planning of new residential areas and how to integrate greenery effectively.
“We probably can’t continue planning as if we’re in an arctic climate. That approach was taken because it used to cost energy to heat houses. Now, it costs energy to cool houses instead. Alternatively, people develop health problems, and we’ve seen an increase in those. It’s simply better to have an outdoor environment that’s more cooling,” says Ulla Mörtberg.
The measurements also highlight how building density affects temperatures. Heat islands emerge where there are many large buildings across wider areas.
“We need to consider how to build in a way that creates a pleasant microclimate for the people living in an area. Greenery is something we can compensate with, and this research can lead to greener cities with more cooling urban environments.”
The researchers will now continue to investigate which tree species are best to plant for cooling. To gather more insights, they are also conducting a heat-related survey for Stockholm residents during the summer of 2025.
“When it comes to microclimates, it’s important to think about which cardinal directions you build in. Regarding trees, they should be a vital part of the construction process, both planting new trees and taking into account existing trees during development,” says Ulla Mörtberg.
Text: Emelie Smedslund, KTH.
Photo: Lennart Backlund
