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The aim of this research was to evaluate the clumped model for estimating latent heat flux (LE) and actual evapotranspiration (ETa) over a non-water-stressed olive orchard. Additionally, submodels to compute the net radiation Rn, soil heat flux G, and canopy resistance were also included. For this objective, a database was used from an experimental unit inside a commercial superintensive drip-irrigated olive orchard located in the Pencahue Valley, Maule Region, Chile (35°23′S, 71°44′W; 96 m above sea level) during the 2009/10 and 2010/11 growing seasons. The evaluation was carried out using measurements of LE obtained from an eddy covariance (EC) system. In addition, estimated values of Rn, G, and were compared with ground-truth measurements from a four-way net radiometer, soil heat flux plates with soil thermocouples, and a portable porometer, respectively. Results indicated that the clumped model underestimated LE and ETa with errors of 11.0% and 3.0%, respectively. Values of the root-mean-square error (RMSE), mean bias error (MBE), and index of agreement dr for LE were 35 W m−2, −1.0 W m−2, and 0.96, while those for ETa were 0.48 mm day−1, 0.04 mm day−1, and 0.64, respectively. The submodels computed Rn and G with errors less than 6% and RMSE values less than 65 W m−2, while the Jarvis-type model predicted with RMSE = 41 s m−1 and MBE = 7.0 s m−1. Finally, a sensitivity analysis indicated that the ETa estimated by the clumped model was significantly affected by variations of ±30% in the values of the LAI and the minimum stomatal resistance rstmin. [ABSTRACT FROM AUTHOR]

To evaluate the partitioning of net radiation ( R) and actual evapotranspiration ( ET), measurements of R, sensible heat flux ( H), soil heat flux ( G), latent heat flux ( LE), reference evapotranspiration ( ET), transpiration ( T) and soil evaporation ( E) were taken during the 2009/2010 and 2010/2011 growing seasons on a flat and uniform olive (cv. Arbequina) orchard, located in the Pencahue Valley, Región del Maule, Chile (35°23′ LS; 71°44′ LW; 96 m above sea level). Olive trees were trained on a triangular hedgerow system with a plant density of 1333 trees ha (superintensive). An eddy covariance system, sapflow sensors and microlysimeter were used to measure ET, T and E, respectively. Results indicated that the eddy covariance measurements showed a lack of the energy balance closure of 12.8 %. Values of LE, H and G were between 28-47, 34-68 and 2-6 % of R, respectively, while ratios of T and E to ET ranged between 0.64-0.74 and 0.26-0.36, respectively. During two growing seasons, the single crop coefficient ( K = ET/ ET) was between 0.27 and 0.66, while the dual crop coefficient ( T/ ET + E/ ET) ranged between 0.26 and 0.56. According to these results, H and T were the main component of R and ET, respectively, for the particular conditions of the drip-irrigated olive orchard with a fractional cover of 30 % and wetted area of 4.5 %. [ABSTRACT FROM AUTHOR]

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 (35º 23'S; 71º 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 d¹ 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. [ABSTRACT FROM AUTHOR]