Quantifying the effects of advection on canopy energy budgets and water use efficiency in an irrigated wheat field in the North China Plain

Competing demands for water with increasing population calls for developing strategies for increasing the crop water use efficiency (WUE) of irrigated crops, especially in the semiarid regions of the world. In this context, it is important to quantify the various factors that control the WUE of irrigated crops in these regions. Advection is an important factor that can have significant effects on the energy exchange in irrigated fields of arid regions, and hence control the crop canopy WUE (CWUE). An eddy covariance system was applied to measure water and heat fluxes and then to quantify advection in an irrigated winter wheat filed at the Yucheng Integrated Experiment Station, Chinese Academy of Sciences in the North China Plain (NCP) (36°57′N, 116°36′E, 28 m a.s.l.) in 2004. Priestley–Taylor parameter and canopy–air temperature differences were employed to identify the occurrence of advection. Effects of advection on canopy energy budgets and CWUE were examined by computing the equilibrium and advective evapotranspiration. It was found that enhanced advection occurs when the crop canopy–air temperature differences are negative or when the Priestley–Taylor parameter takes on values >1.5. Due to enhanced advection, the percentage of latent and sensible heat flux exchange contribution to the total water loss from the fields through evapotranspiration can exceed 50%, and CWUE decreased remarkably. Advection in the experiments probably resulted from drier soil regimes in the upwind areas.