No access parameterization of a clumped model to directly simulate actual evapotranspiration over a superintensive drip-irrigated olive orchard

Abstract

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 rsc 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 rsc 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 rsc 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.