Measurement and Estimation of Evapotranspiration

Evapotranspiration is a major term of the soil water balance. Knowing the amount of water directly evaporated from the soil or through transpiration of plants is a point of interest not only for agronomists but for meteorologists, hydrologists and irrigation project managers. A large number of papers have been published in the last thirty years concerning both mechanisms, measurements and estimation techniques (for review see e.g. Brutsaert 1982, Seguin et al. 1982, Hatfield and Fuchs 1990, Jensen et al. 1990, Allen 1994). The aim of this paper is not only to review what is available today, for different time and space scales but also to see how it could be used by farmers or more generally by project managers. Recommendations are made to improve both knowledge and transferability to users.