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 transaction is still a challenge today given the significance of evapotranspiration for a basin’s hydrology. Consequently, much research has been devoted to this topic. However although there have been many advances in meteorological equipment and observations, more universal recognition of the impact of climate and land cover changes on evaporation and hydrology, and the increased accessibility of many parts of the world, evaporation from much of the globe remains elusive to quantify.

This is particularly true in areas with few meteorological observations, in regions where precipitation is particularly hard to predict such as in semi arid or mountain environments, and in places where are strong effects of unpredictable climate oscillations. These often correspond to places where climate change has already had a great impact and where changes in evaporation demand have a large impact on downstream hydrology. In this session we want to focus on quantifying evapotranspiration dynamics in diverse climates and environments as a tool for improving hydrologic assessments and predictions at a catchment scale. We are interested presentations that discuss:

- Sensitivity of ET models under highly variable climate conditions (observational and modelling approaches)
- Potential hydrological impacts under harder to predict precipitation regimes,
- Modelling ET approaches designed to cope and deal with the effects of this unpredictable climate oscillations
- Datasets that show about ET dynamics in extreme climate areas or places where changing climate is predicted to have a strong impact such as alpine ecosystems, drylands, or areas affected by El Niño or other altered ocean-climate dynamics)
- Spatio-temporal variability of actual ET and its consequences for hydrology at diverse scales
- Trends and effects of changing climate and land use on evapotranspiration and evaporative demand and its driving forces.


For more general sessions on evapotranspiration (including scaling issues), see HS10. For an ET session with a special focus on arid and semi-arid sessions, see HS6.5.