EGU2020-19013
https://doi.org/10.5194/egusphere-egu2020-19013
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modelling the cooling potential of street trees at city-scale with COSMO-BEP-Tree

Gianluca Mussetti1, Dominik Brunner2, Stephan Henne2, Scott Krayenhoff3, and Jan Carmeliet4
Gianluca Mussetti et al.
  • 1Dept. of Civil, Environmental and Geomatic Engineering , ETH Zurich, Switzerland
  • 2Laboratory for Air Pollution/Environmental Technology, Empa, Switzerland
  • 3School of Environmental Science, University of Guelph, Canada
  • 4Chair of Building Physics, ETH Zurich, Switzerland

Street trees are more and more regarded as a potential measure to mitigate the excessive heat in urban areas resulting from climate change and the urban heat island. However, the current knowledge of the cooling effect of street trees relies on studies at the micro-scale while potential interactions at the city-scale are yet to be understood. In fact, the vast majority of large-scale modelling studies only represent street trees outside the street canyon, neglecting important effects such as the shading and sheltering.

In order to explicitly represent street trees in coupled urban climate simulation, the multi-layer urban canopy model BEP-Tree was coupled with the regional weather and climate model COSMO-CLM. The coupled model, named COSMO-BEP-Tree, enabled simulating the radiative, flow and energy interactions between street trees, canyon surfaces and the atmosphere during weather and climate simulations.

In this study, COSMO-BEP-Tree is used to model the cooling potential of street trees during a heatwave event in Basel, Switzerland. The impact of street trees is explored in terms of near-surface air temperature and thermal comfort. The impact of greening scenarios is simulated and compared with other heat mitigation strategies.

The results highlight contrasting urban climate effects of street trees during daytime and night-time, where different processes become dominant. The daytime cooling was primarily a local effect and proportional to the local density of street trees.  In contrast, the impact was more widespread at night, where city-scale interactions become important. Beside air temperature, the model results suggest a significant impact of street trees on wind speed and canyon surface temperature. Owing to these effects, street trees produced a larger impact on thermal comfort than on air temperature. Finally, the need for further model development with respect to urban hydrology is outlined.

How to cite: Mussetti, G., Brunner, D., Henne, S., Krayenhoff, S., and Carmeliet, J.: Modelling the cooling potential of street trees at city-scale with COSMO-BEP-Tree, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19013, https://doi.org/10.5194/egusphere-egu2020-19013, 2020

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