Abstract
The concept of potential evapotranspiration, as applied to arid regions, is examined using an energy balance approach suggested by Budyko. Using data for Yuma, Ariz., it is shown that a 50 per cent increase in the relative humidity of the air above an irrigated field is accompanied by a 10 to 15 per cent decrease in potential evapotranspiration, a negligible decrease in the net radiation, and a temperature increase of the surface relative to the air of 2 to 3C.
The estimated annual potential evapotranspiration at Yuma is about 2000 mm, which is 30 to 50 per cent higher than estimates based on Thornthwaite's method.
