Using the FAO-56 dual crop coefficient method over an irrigated region as part of an evapotranspiration intercomparison study

Evapotranspiration (ET) calculations were made on a daily basis throughout 1988 for two locations near Menemen, Turkey. Calculations used the FAO-56 "dual" crop coefficient approach that includes separate prediction of evaporation from soil. Two days were drawn from the data set to correspond with Landsat flyovers to provide for comparison with remote sensing estimates of ET. One study site was a cotton field in a relatively flat, irrigated region. The second study site was an integrated area in the Gediz River Basin where the farm and held sizes are small, of the order of 3-5 ha, and about ten different "crops" are grown. Predicted ET (ETc act) for the cotton site was 3.1 and 5.3 mm/day for 26 June and 29 August, and was 4.9 and 4.3 mm/day for the integrated crops in the Gediz valley. Total calendar year ETc act was predicted to be 800 for cotton and 940 mm for the Gediz valley. Evaporation during the crop growing periods averaged 9% of total evapotranspiration for cotton and 14% for the mixed crops. The predictions of ETc act were within 20% of predictions by the Landsat-based SEBAL remote sensing method at only one site and date. Predictions were within 20% of ET based on an energy feedback remote-sensing application using NOAA-AVHRR and Landsat data for both sites on one of the two dates. Before comparison, the predictions of ETc act by the FAO-56 procedure were reduced by 15%, to account for less than pristine crop establishment, growth and water management in the area. (C) 2000 Elsevier Science B.V. All rights reserved.