ABSTRACT
A vast amount of literature describes the determination of evaporation and evapotranspiration under varying climatic and agricultural circumstances. Recently, the FAO published new practical guidelines for computing crop evapotranspiration (as Publication 56; Allen et al. 1998), replacing the classical Irrigation and Drainage Report 24 (Doorenbos & Pruitt 1977). In these reports the calculation of reference crop evapotranspiration (ET0) (formerly called potential evapotranspiration) and actual evapotranspiration under standard and non-standard conditions is described in great detail, at the same time providing a large number of references to the scientific work underlying developments in this particular field of applied science. Furthermore, standard hydrological textbooks such as Dingman (1994) give clear accounts of the physical background of evaporative processes.
