- The influence of well-watered trees on urban microclimate was investigated.
- A canyon street scale-model (1/5) in outdoor environment was instrumented.
- Climatic parameters, tree transpiration, and soil water status were measured.
- Trees reduced air and wall temperatures, cancelling out urban overheating.
- Trees reduced the level of heat stress, as measured by UTCI, in the canyon street.
Cities experience overheating due to factors such as urban form and materials, concentration of human activities, reduction in the amount of vegetation and water surfaces. Vegetation is one of the ways to reduce temperature peaks in the city during heat waves. The objectives of this paper are twofold: first, to study the impact on the microclimate of a north-south oriented canyon street at reduced-scale (1/5), then to study the impact of well-watered trees on the street microclimate. This study provides a highly integrated view of climatic mechanisms through the measurement of a set variables, including air temperature, relative humidity, wall temperature, conductive and radiation fluxes as well as tree transpiration and thus allows a better understanding of the physical phenomena at stake. It shows that the canyon street created an urban overheating of up to 2.8 °C during the night, and up to 2.4 °C during the day, and that trees reduced the air temperature in the street by up to 2.7 °C during the day. Finally, trees improved human thermal comfort with a reduction of 8 °C of the Universal Thermal Climate Index at midday.