Climatic benefits of street trees on the microclimate and thermal comfort: an in-situ experiment in paris

31st International Horticultural Congress, Angers, FRANCE, 14-/08/2022 - 20/08/2022Global warming is accompanied by a multiplication of extreme events such as heatwaves. In cities, this phenomenon is amplified by the urban configuration and the nature of the materials whose optical and thermal properties enhance overheating. Vegetation appears to be a solution to partially overcome this issue. Trees in particular offer two main benefits: cast shadows and evapotranspiration. But, the evolution of such climatic benefits during warm and dry periods as well as their dependence on the tree species remain poorly quantified. In this context, the green spaces department of the city of Paris monitored the microclimate (air and globe temperature, air relative humidity and wind speed) inside the crowns of 9 trees, representing 5 different species, and on 3 reference lamp posts located in a Paris canyon street during a 22 days summer period in 2020. All trees were able to counteract the diurnal overheating generated by the street and provided an efficient human thermal stress improvement all along the period which was dry and included 2 heatwaves. Ulmus Resista appeared to be on average more efficient than Sophora Japonica but the differences between individuals remained low (from 2.8 °C to 4.1 °C reduction were calculated on average during daytime on sunny days regarding the Universal Thermal Climate Index). Further analysis will take into account other periods of time, more individuals and will try to assess their access to water in order to provide stakeholders guidance on how to maximize the climatic benefits of street trees