FAO-56 dual approach combined with multi-sensor remote sensing for regional evapotranspiration estimations

Abstract. The aim of this paper is to use a dual, modified version of the FAO-56 methodology for the estimation of regional evapotranspiration. The proposed approach combines the FAO-56 technique with remote sensing. Two vegetation classes are considered in the evapotranspiration estimations. In the case of cereals, crop coefficients and cover fractions are estimated using relationships established with the Normalized Difference Vegetation Index (NDVI), retrieved from SPOT-VGT data. In order to characterize the soil, a relationship is established between evaporation and the retrieved soil moisture values, based on the ERS/WSC products developed by the University of Vienna. This approach is applied to a semi-arid region in central Tunisia (North Africa) and is validated over 1991–2007 period using simulations from the ISBA-A-gs physical SVAT model. The ISBA soil moisture outputs are validated using remotely sensed ERS/WSC products. Finally, a comparison is made between the ISBA and FAO approaches, for the same studied site.