In the present century, for the first time in history, the urban population overpassed the rural one. Cities are growing, and their impact on the world energy balance is significant. Consequently, a sustainable urban environment focusing on the reduction of the energy demand of buildings, as well as the improvement of the environmental conditions is essential. In this context, a key aspect to address is the landscape design, and its impact on the urban energy balance. In order to address this point, we propose a new methodology to quantify the impact of the evapotranspiration, from grass, on the energy demand of building, as well as on the surface temperature of the city. The new model is applied to “La Jonction” district in the city of Geneva, focusing on the current and future impact of the evapotranspiration within the urban context. Indeed, by introducing grass and cooling materials within the urban context, the surface temperature of the site decreases by 2.5 °C on average per year, and up to 5 °C during the month of July. These results underline the positive impact of greening and cooling materials on the urban thermal behaviors, in the current and future climatic scenario.