Coupling hydrological and microclimate models to simulate evapotranspiration from urban green areas and air temperature at the district scale

Understanding and managing hydrological and microclimate conditions is needed for the adaptation of our cities to global warming. Evapotranspiration, or latent heat flux, plays a key role in heat mitigation strategies. Its modelling, as the modelling of its impact on the urban microclimate, remains a scientific challenge, especially during hot periods for which the urban vegetation is subjected to water stress. This article presents an original approach based on the coupling between a hydrological model and a microclimate model to assess the effect of urban green areas on evapotranspiration and air temperatures at the district scale. The approach is applied to a real urban development project, and under future climate conditions. The results show a complex variability of climatic and hydrological behaviour depending on the green zones considered. Results indicate that the water stress control over evapotranspiration can have a significant impact on local surface and air temperatures (respectively 3 to 6 ◦C and 0.6 and 1.6 ◦ C difference as compared to ideal water availability conditions).