The use of actual evapotranspiration (
ETa) models requires an appropriate parameterization of the available energy, where
the net radiation (
Rn) is the most important component. Thus, a study was carried out to calibrate and evaluate three semiempirical
approaches to estimate net radiation (
Rn) over a drip-irrigated olive (
Olea europaea
L. ‘Arbequina’) orchard
during 2009/2010 and 2010/2011 seasons. The orchard was planted in 2005 at high density in the Pencahue Valley, Maule
Region, Chile. The evaluated models were calculated using the balance between long and short wave radiation. To achieve
this objective it was assumed that
Ts =
Ta for Model 1,
Ts =
Tcv for Model 2 and
Ts =
Tr for Model 3 (
Ts is surface temperature;
Ta is air temperature; and
Tcv is temperature inside of the tree canopy;
Tr is radiometric temperature). For the three models,
the Brutsaert’s empirical coefficient (φ) was calibrated using incoming long wave radiation equation with the database of
2009/2010 season. Thus, the calibration indicated that φ was equal to 1.75. Using the database from 2010/2011 season, the
validation indicated that the three models were able to predict the
Rn at a 30-min interval with errors lower than 6%, root
mean square error (RMSE) between 26 and 39 W m
-2 and mean absolute error (MAE) between 20 and 31 W m
-2. On daily
time intervals, validation indicated that models presented errors, RMSE and MAE between 2% and 3%, 1.22-1.54 and
1.04-1.35 MJ m
-2 d
-1, respectively. The three
Rn-Models would be evaluated and used in others Mediterranean conditions
according to the availability of data to estimate net radiation over a drip-irrigated olive orchard planted at high density.
