Last week we restarted the project URBTREES, in which we investigate the effect of tree transpiration on urban heat island mitigation. For this, we installed sap flow sensors on eight Platanus trees on a town square in the city of Lancy, near Geneva. The sensors will continuously measure how much water the trees transpire during the entire growing season. In addition, we put small meteo stations in the tree canopy and on the street lamps of the town square that measure air temperature and relative humidity. We will combine the transpiration and climate measurements to calculate how much the platanus trees cool down the town square with their transpiration with a high temporal resolution.
We expect to find a high transpirational cooling of the trees during hot days in summer, but we also hypothesise that during extended dry periods, the cooling effect will be reduced, because the trees will close their stomata to prevent desiccation. It was great to see the high interest of the local people in the town square for this research project as we were installing the sensors.