On April 26th, the first EVNATURB evapotranspiration campaign was carried out on the Blue Green Wave, in front of École des Ponts ParisTech. The campaign aims at estimating evapotranspiration flux in different locations to assess its variability in space and time. With this purpose, a portable transpiration chamber developed by David Ramier (Cerema Île de France) was used. It contains several sensors: temperature probes, a gaz analyser to estimate absolute humidity, and a radiometer to assess net radiation. Absolute humidity is measured during 1 minute after the chamber implementation on the vegetated surface. During this period of time, a linear relationship between evapotranspiration and humidity variation is maintained. Further campaigns are planned in the next (spring and summer) months. These measurements will be coupled with TDR water content and scintillometer measurements to assess the different components of the energy balance.