Analyzing the Areas Contributing to Evapotranspiration Measured from the Eddy Covariance System in a Winter Wheat Field.

(Background and objective) Evapotranspiration from managed and natural ecosystems is an important process in hydrological cycle but not trivial to measure at large scales. The eddy covariance developed over the past decade is a technique to measure atmospheric turbulent fluxes which can be used to estimate evapotranspiration and fluxes of other gases. Calculating evapotranspiration from the measurements of eddy covariance is complicated, and the aim of this paper is to experimentally investigate the areas in a farmland system that contribute to the fluxes measured from an eddy covariance. (Method) Atmospheric fluxes were measured from October 2019 to June 2020 using the closed-path eddy covariance system installed in a winter wheat field at Xinxiang comprehensive experimental station in Henan province. Distribution and variation of the measured flux sources were analyzed using the footprint models and FFP and KM methods. (Result) 1 Southwest-northeast wind was the dominant wind during the experimental period, following by northeast-southwest wind. 2 The results calculated under different growth stages and atmospheric conditions revealed that the areas that contributed to the fluxes measured from the device were larger under stable atmospheric conditions than under less stable atmospheric conditions. The direction and length of the areas were affected by wind direction and speed. 3 The results calculated by the FFP and KM models showed a linear relationship between the source areas with SKM=0.93SFFP-1962.5 and R&#178=0.96, and that, in the general, the areas calculated by the KM method were greater than that calculated by the FFP model. (Conclusion) The flux source areas calculated by the FFP and KM methods differed, and the wind direction and speed were the main factors affecting the flux source distribution. For our experiment, the winter wheat was the main contributor to the fluxes measured from the eddy covariance system. [ABSTRACT FROM AUTHOR]