How do the city’s trees and greenery impact the indoor climate? This is being investigated by a research team at KTH, in collaboration with the City of Stockholm and ElectriCITY, as part of the DigiCityClimate project. Over the summer, measurements have been taken using cargo bikes, waste trucks, and feedback from residents in Hammarby Sjöstad. The goal is to generate new insights into how cities of the future should be planned and built.
We live in an increasingly warmer climate, and cities are especially affected by heat. In Stockholm, there are 180 heat islands larger than one hectare, where temperatures exceed 35°C during heatwaves. However, it’s not equally hot everywhere.
– In Stockholm, like in many other large Nordic cities, buildings are designed to retain heat, not to keep it out. So, what options do we have to create cooling without relying on energy? Trees and greenery are part of the solution, says Ulla Mörtberg, professor at KTH.
The role of trees and greenery goes beyond just providing shade. When it rains, some of the water is captured by the leaves of the trees, where it then evaporates back into the atmosphere. Trees also transport water from the ground through their trunks and branches to the leaves, where it evaporates again. This process affects the temperature.
Combining Multiple Measurements
What makes this research project unique is that it combines different types of temperature measurements to provide a comprehensive understanding of how trees and greenery affect both outdoor and indoor temperatures, as well as perceived heat.
In Hammarby Sjöstad, KTH students have been riding cargo bikes equipped with scanners that measure temperatures on various surfaces throughout the area. Waste trucks in Hammarby Sjöstad have also been fitted with scanners on their roofs to collect data during the summer months. Additionally, residents have participated by completing surveys to share how they experience heat both indoors and outdoors.
– We know that trees and greenery provide shade, but we don’t yet fully understand the overall impact of trees. For example, how tall do the trees need to be to influence how residents perceive indoor heat? These are some of the questions we hope to answer, which could help improve the planning process for future city developments, says Ulla Mörtberg.
DigiCityClimate
This heat project is part of the larger DigiCityClimate initiative, which aims to support the City of Stockholm in meeting its climate and sustainability targets. It includes the development of technology that empowers citizens to take control of their energy transition and sustainability efforts — enabling them to monitor and reduce their own energy and climate impact.
The project has three main tracks:
• Develop an AI-driven energy advisor chatbot to guide citizens in making climate-efficient energy investments.
• Provide the city with climate models and data to support urban planning for a sustainable microclimate. • Develop a digital control room to offer housing cooperatives increased transparency and the ability to manage their building’s energy use.
This project is a collaboration between KTH, the City of Stockholm, and ElectriCITY Innovation, funded by the ICLEI Action Fund with a grant from Google.org. Hammarby Sjöstad is serving as the testbed for the project.
Segment on SVT Stockholm
SVT Stockholm was on-site when the measurements with the cargo bikes began. The segment can be viewed here.