Short-term estimation of sorghum evapotranspiration from canopy temperature

Abstract

This study was conducted to compare calculated evapotranspiration ( ET c) values using canopy and aerodynamic resistances derived by two methods with measured evapotranspiration ( ET) from a weighing lysimeter. Grain sorghum ( Sorghum bicolor (L.) Moench) mean potential canopy (r̄ cp) and aerodynamic (r̄ ap) resistances were estimated from the linear relationship between sorghum canopy minus air temperature and air vapor pressure deficit. Additionally, wind speed-dependent aerodynamic resistance ( r a) estimates were used. High-frequency short-term (10 min) estimates of crop evapotranspiration were made under clear and partly cloudy sky conditions. The agreement between ET c and measured ET from the lysimeter was optimum when r̄ cp and the wind speed-dependent r a were utilized ( r=0.95, RMSE=0.06 mm h −1, MB=−0.042 mm h −1) during clear sky conditions. On a day with partly cloudy sky conditions, the relationship was slightly less correlated ( r=0.81, RMSE=0.12 mm h −1, MB=−0.036 mm h −1) but the method's ability to track rapidly changing ET rates was notable. Short-term or high-frequency estimates of ET could be useful for crop-level physiological studies of response to water stress, and irrigation water management research.