In most of the important agricultural regions of the world, evaporation in the growing season exceeds the precipitation, and also often the sum of precipitation and plant available water in the root zone. This causes a need of supplemental irrigation for effective agricultural use. Information about the greatest possible water consumption in given periods, therefore, is important for the water policy of a given region.

Several methods for estimation of the maximum (potential) evaporation have been suggested, and many methods have been compared earlier (W.M.O. 1966, Heldal 1969, Kristensen 1971, Iruthayaraj and Marachan 1978).

In Denmark a screened sunk iron pan has been used as a standard since 1956 (Aslyng and Hansen 1960). This standard pan and other methods for estimating potential evaporation have been compared during a 15-year period. The results are reported and discussed.