Assessing the discrepancy of energy fluxes over spring wheat under sloping topography conditionsbased on eddy covariance measurements

Accurately quantifying surface energy budgets in croplands is essential for efficient water resource allocation and sustainable agricultural practices. However, the representativeness of eddy covariance (EC) measurements in hilly agricultural fields remains less examined. In this study, we conducted an experiment employing three EC flux towers to assess the consistency of surface energy budget components across a hilly agricultural field (~90 acres). The experimental field was divided into three zones, each equipped with an EC tower positioned at its central location to ensure that 90% of the flux footprint fell within the corresponding zone (i.e., US-SZ1, US-SZ2 and US-SZ3). The meteorological conditions and energy fluxes were found to be significantly influenced by various agricultural activities, including both growing and non-growing periods, as well as cropland management practices. Despite relatively similar meteorological conditions observed across the three sites during the wheat growing period (WGP), substantial discrepancies were evident in the primary energy budget components, with the exception of net radiation, at both diurnal and seasonal scales. During WGP, the sensible, latent, and ground heat fluxes exhibited differences within 10%, 27%, and 29%, respectively, leading toconsiderable disparities in the energy balance closure. The closure ratios (CRs) for US-SZ1, US-SZ2, and US-SZ3 were approximately 93%, 84%, and 85% respectively. The influence of environmental variables on the discrepancies in their CRs were also investigated. The relationships between CRs and friction velocity, atmospheric stability, turbulent kinetic energy, as well as heat transport efficiency exhibited certain distinctions among the three sites. Our findings indicate that factors like site elevation, topography, and measurement uncertainty differentially affect energy flux components in sloping landscapes. Employing multiple tower/point measurements is crucial for reducing uncertainties in energy flux estimates under sloping terrain conditions.