Evaporation Rate of a White Class A Evaporation Pan

Abstract

This study experimentally investigates the influence of color on the evaporation rate of a Class A evaporation pan. Two Class A evaporation pans, one in the original galvanized metal color and the other painted white, are placed in the same meteorological station for 18 months. Since the wind speed, air temperature, and vapor pressure deficit are the same for both pans, the color and the resulting net radiation are the only causes for differences in the evaporation rate. The results reveal that the average net radiation of the white pan is about 90% that of the metal-colored pan. This leads to the annual evaporation rate of the white pan (1,041 mm year−1) being only 75% of the evaporation rate (1,392 mm year−1) of the metal-colored pan. In addition, the prediction error of the daily evaporation rates by the energy budget method is lower than that of the Penman-Monteith type models. The differences between the measured evaporation rates of the two pans are analyzed to examine the role of irradiance on the pans’ evaporation rate. The results indicate that the irradiance absorbed by the pan wall can affect the energy budget and evaporation rate of the pan.