Understanding the physical and thermal processes that govern Bleu Green Solutions (BGS), such as evapotranspiration (ET), is one of the challenges of urban hydrology to determine their possible impacts to mitigate urban heat islands. Evaluate the ET process in BGS, specifically in the green roof installed in front of the Ecole de Ponts, is the main objective of this work. Hence, three different direct and indirect methods have been tested and compared to estimate ET: (i) a soil moisture content measurement via a wireless sensors network and by using the water balance, (ii) an absolute humidity measurement provided by a dynamic transpiration chamber, and (iii) an indirect method based on the energy budget and by using a scintillometer to assess the sensible heat flux. In a second time, the spatial and time variability of the measured ET flux will be evaluated by multifractal tools, allowing to assess this hydrological process through different scales.