More than 50 years ago John Monteith pointedly wrote that “evaporation of water is like a commercial transaction in which a wet surface sells water vapour to its environment in exchange for heat”. The spatio-temporal measurement and modelling of the details of this “commercial transaction” however still is a challenge today. Additionally, a significant part of the hydrologic activity in a basin is determined by evapotranspiration. Consequently, much research has been devoted to this topic, as summarized in the seminal book of Wilfred Brutsaert’s “Evaporation into the Atmosphere”. However, this term in the water balance remains difficult to reliably quantify, in particular on scales relevant for catchment hydrology. This session therefore welcomes contributions from different disciplines not only on theoretical aspects, as well as modeling and measurement of spatio-temporal variability of actual evapotranspiration, but also on evaporative demand. Contributions on the following are strongly encouraged:

- Novel techniques for measuring and modelling evapotranspiration, from in situ methods to remote sensing techniques, and from ground-based devices, UAVs to spaceborne platforms.
- Novel approaches to modelling the space-time variability of evapotranspiration, including upscaling procedures.
- Applications of measured and/or modelled evapotranspiration in catchment hydrological models for the purpose of process understanding or predicting hydrological response.
- Trends and effects of changing climate and land use on evapotranspiration and evaporative demand and its driving forces.