Investigation on performance of evapotranspiration temporal upscaling methods based on eddy covariance measurements

Evapotranspiration (ET) temporal upscaling method plays an essential role in ET remote sensing. In order to compare the performance of evaporative fraction method, crop coefficient method and canopy resistance method to upscale daily ET from daytime measurements, the daytime variation of evaporative fraction, crop coefficient and canopy resistance were investigated and the performance of three methods were assessed. The field work was carried out in Daxing district under winter wheat surface from March to June and the ET data was measured by eddy covariance. The results showed that the crop coefficient was more constant during daytime than evaporative fraction and canopy resistance, and the closeness of daily value and hourly value for crop coefficient was better than other two parameters. Meanwhile, the crop coefficient method performed better to upscale daily ET than other two methods. It is recommended to choose crop coefficient method to upscale daily ET data for the areas with similar climate, underlying surface conditions and data with similar spatial scale in Daxing district.