Potential Evapotranspiration as Influenced by Wind1

Abstract

AbstractThe contribution of wind to calculated potential evapotranspiration was investigated with applications for the climate of the Great Plains. A revised combination model proposed by van Bavel for computing instantaneous potential evapotranspiration was used. The model contains two terms that are expressions for the portions of potential evapotranspiration primarily due to net radiation and wind, respectively. With ambient water vapor pressure 20 mb, temperature 30C, wind 2, 4, and 6 m sec−1 at 2 m with a roughness length of 1 cm, contribution of wind dominant term to evaporation from a wet surface is 0.15, 0.30, and 0.45 mm hr−1, respectively. At 10‐mb vapor pressure and the same temperature, the corresponding evaporation rates are 0.22, 0.43, and 0.65 mm hr−1. On representative and consecutive “nonwindy” and “windy” days at Manhattan, Kans. (average daily windspeeds at 45 cm were 0.88 and 2.26 m sec−l), the wind dominant term contributed 33 and 113%, respectively, as much as the radiation dominant term to the total calculated potential evapotranspiration. For these 2 days the ratio of potential evapotranspiration to net radiation was 0.98 and 1.60.