Actual and Reference Evapotranspiration in a Cornfield in the Zhangye Oasis, Northwestern China

摘要

Evapotranspiration ( ET ) is an important component of the surface energy balance and water cycle, especially in arid and semiarid regions. The characteristics of the actual evapotranspiration ( ET a ), which was calculated using the eddy covariance method, and the reference evapotranspiration ( ET 0 ), which was estimated using the Food and Agriculture Organisation (FAO) Penman–Monteith method, were analysed. This work focussed on the seasonal variations in evapotranspiration and crop coefficient ( K c ) above the heterogeneous canopy of an arid oasis ecosystem in a cornfield of the Zhangye oasis in northwestern China. The results showed that in 2008, the total net radiation ( R n ) was 2457.73 MJ?m ?2 and that the rainfall was 117 mm. The average wind velocity, air temperature, and specific humidity, which were observed 2 m above the ground surface, were 1.23 m?s ?1 , 7.07 °C, and 3.66 g?kg ?1 , respectively. The total ET a and ET 0 were 654.69 mm and 1039.92 mm, respectively; thus, the ET 0 was higher than the ET a . The difference between the ET 0 and ET a was high in summer and autumn, and low in winter and spring. The ET a was greatly influenced by irrigation events, whereas the ET 0 was not influenced by irrigation. The ET a and ET 0 were both greatly influenced by meteorological elements. The K c values were less than 0.5 outside of the maize-growing stage and greater than 0.5 during the entire maize-growing stage (from 20 April to 22 September 2008). The K c values were 0.63, 0.75, 0.78, 0.76, 0.61 and 0.71 at the seedling, shooting, heading, filling, and maturity stages and the entire growth stage, respectively.