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Validation of a Two-Layer Model to Estimate Latent Heat Flux and Evapotranspiration in a Drip-Irrigated Olive Orchard

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 55(4): 1169-1178. (doi: 10.13031/2013.42237) @2012
Authors:   S. Ortega-Farías, R. López-Olivari
Keywords:   Canopy resistance, Energy balance, Evapotranspiration, cv Arbequina

A two-layer model was evaluated to simulate latent heat flux (LE) and evapotranspiration (ET) of a drip-irrigated olive orchard during the 2009-2010 and 2010-2011 growing seasons. This orchard is located in the Pencahue Valley, Maule Region, Chile (35 23' S; 71 44' W; 96 m above mean sea level). A constant canopy size was maintained during the two study periods, with leaf area index (LAI) and fractional cover (fc) ranging between 1.29 and 1.34 m2 m-2 and between 0.29 and 0.30, respectively. In addition, the olive orchard was maintained under non-water-stressed conditions, with a midday stem water potential greater than -1.96 MPa. The LE and ET obtained from the eddy covariance (EC) system were used to validate the performance of the two-layer model. The validation including the two study periods indicated that mean values of root mean square error (RMSE) and index of agreement (Ia) for latent heat flux were 28 W m-2 and 0.98, respectively, while the RMSE and Ia values for olive evapotranspiration were 0.52 mm d-1 and 0.84, respectively. This study also indicated that the two-layer model overestimated LE and ET by about 2% and 6%, respectively. Finally, results indicated that the model was very sensitive to errors in the measurements of stomatal conductance and LAI. Major errors of the two-layer model to simulate ET directly were associated with very dry atmospheric conditions (vapor pressure deficit between 3.5 and 4.5 kPa) observed during the afternoon. However, the main errors did not significantly affect the overall performance of the two-layer model.

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