Impact of evapotranspiration on the local microclimate

Climate change is having and will have drastic consequences for high density populated areas such as cities. There is thus a need to develop more tools to evaluate new strategies for adaptation to and mitigation of changing temperatures. Additional functionalities were integrated in the urban energy modelling tool CitySim to include an evapotranspiration process and to integrate low rise vegetation as well as trees. In the process, the Canopy Interface Model (CIM) – previously coupled with CitySim – was further developed to integrate the evapotranspiration process and to analyse its impact on the local microclimate. Tvapotranspiration as well as the surface temperature are computed in CitySim and the values are then used as boundary conditions in CIM to calculate the vertical profiles of wind speed, temperature and humidity. Using the campus of the EPFL in Lausanne, Switzerland as a case study, it was demonstrated that the ground evaporative cooling can be an effective mitigation measure for decreasing locally the urban heat island intensity. In future studies, other strategies such as reflective asphalt, will be combined with the evaporative cooling strategies, to determine the most effective action measures that could be easily implemented.