ObjectiveEstimating evapotranspiration (ET) based on the semi-empirical and semi-theoretical Priestly-Taylor model (PT) mainly relies on accurately determining the appropriate value of the model coefficient α in a specific study area. This study expored the applicability of the model coefficient α. Localization studies have been conducted to more accurately estimate evapotranspiration in arid and semi-arid regions.
MethodThis paper used the eddy covariance technique combined with micro-meteorological data to monitor the water and heat transfer processes of a typical Artemisia ordosica shrubland in growing season in Mu Us Sandy Land of northwestern China to quantify the seasonal variations in α coefficients.
ResultThe results showed that the actual α coefficient had significant seasonal variations, peaking during the leafing period, and remaining relatively plateau during expanded leaf period and the leaf discoloration period. The maximum α coefficient was 0.66 and the minimum value was 0.03, averaging 0.23 in growing season. There was a logarithmic positive correlation between α coefficient and canopy conductance and saturated vapor pressure difference in the growing season. Soil water content (30 cm belowground) and leaf area index were positively correlated with α coefficient. Evapotranspiration estimated from the PT model with α=1.26 and with α=0.50, which was calculated from the wind speed data at 2 m height, was significantly larger than the measured evapotranspiration. The recommended localization value of the improved PT model coefficient α was 0.23, which gave better estimation of ET, linear gradient was 0.72, R2 was 0.57.
ConclusionTherefore, the modified PT model can be used to accurately estimate evapotranspiration in arid and semi-arid regions.