Eddy covariance fluxes versus satellite-based modelisation in a deficit irrigated orchard

This study describes a combined approach to determine actual evapotranspiration (ETa) fluxes in a deficit irrigated orchard in Sicily, Italy. Different ET models mostly based on satellite data (i.e., surface energy balance models: one source ET1S-two source ET2S, and vegetation indexes derived crop coefficient model, ETVI) were compared with both direct ET measurements obtained in situ by the Eddy Covariance (EC) technique (ETEC) and crop ET (ETc) calculated by FAO-56 approach. Results of the comparisons show a general overestimation of the latent heat flux (or ET) by the satellite models and estimated ETc, respect to the direct ETEC data. This discrepancy can be the consequence of the deficit irrigation regimes (i.e. ranging from a minimum reduction of about 15% to a maximum of 45% of ETc) applied at the experimental orange orchard, which may have caused a high source of sensible heat flux, driven by the temperature gradient between plant canopy-atmosphere continuum.