Utilizing urban land surface model SUEWS to estimate effects of green infrastructures to carbon and heat balances in Zürich, Switzerland

As cities face the drastic effects of climate change, they must simultaneously focus on reducing carbon dioxide (CO₂) emissions, mitigating these emissions, and adapting to the changes. Green urban infrastructures hold an important role in both mitigation and adaptation. Green spaces, such as parks and street trees, act as carbon dioxide sinks and contribute to carbon storage while providing cooling effects through shading and transpiration.

In this study, the urban land surface model SUEWS (Surface Urban Energy and Water balance Scheme) is used in the city of Zürich, Switzerland, to study the combined effect of urban green infrastructures in a spatial scale and to explore how these effects vary across the city based on canopy coverage. The model can jointly simulate water, CO₂ and heat exchanges, and requires meteorological information and surface cover related parameters as input. The study covers the period from July 2022 to June 2023, with the first half of 2022 serving as the spin-up period. To evaluate the model's performance, eddy covariance (EC) measurements of CO₂, latent and sensible heat flux were recorded at the 111-meter-tall Hardau II tower.  The ICOS Cities rooftop temperature sensor network was used to assess simulated temperature variations.

Results show that the forests surrounding the city are the most prominent CO₂ sinks, but in the city center urban parks also act as sinks. The latent heat flux is the largest in the vegetated areas and sensible heat flux in the built-up parts. The area surrounding the EC tower is highly influenced by the anthropogenic emissions, making it challenging to discern the sinks of urban green vegetation in the model and the measurements. The model is able to catch the variations in temperature at different locations in the city. The results will be evaluated against canopy coverage of the city.