Estimation of water requirements for an irrigated hazelnut (Corylus avellana L.) orchard using Landsat satellite images

A study was carried out to validate the METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) model to estimate the spatial variability of water requirements for a drip and micro sprinkler irrigated European hazelnut orchard (1,500 ha) located in Maule Region, Chile (35°18’ S 71°21’ W; 219m above sea level). To estimate hazelnut water requirements (actual evapotranspiration (ET) and crop coefficient (Kc)) using the METRIC model, Landsat 7 ETM+ and 8 OLI satellite images acquired during clear sky days were used for the 2016-2017 growing season. The performance of METRIC was evaluated in an experimental block (4,5 ha) located within the orchard using measurements of ET from an eddy covariance (EC) system at the time of satellite overpass (11:30 h). The statistical analysis indicated that the original METRIC model overestimated ET values by about 42%. After calibrating sub-models for estimating leaf area index (LAI), roughness length (Z_om), and soil heat flux (G), METRIC estimated ET with errors < 10 %, root mean square error (RMSE) = 0.98mm d^-1, mean absolute = 0.90mm d^-1 and index of agreement = 0.70. Results suggested that the calibrated version of METRIC could be a valuable tool for mapping the spatial and temporal variability of ET and Kc for a drip-irrigated hazelnut orchard.