PERFORMANCE OF THE SAFER MODEL IN ESTIMATING ACTUAL EVAPOTRANSPIRATION OF WHEAT AND BEAN IRRIGATED CROPS IN THE CENTRAL BRAZILIAN SAVANNAH

Abstract

Meeting the ever-growing demand for food depends tightly on irrigation. In this scenario, it is essential to manage the scarce water resources available and so to understand the spatial and temporal variation of actual evapotranspiration (ETa). In the past decades, models for monitoring and mapping ETa applying remote sensing data were developed and assessed. In this work, the performance of the Simple Algorithm for Evapotranspiration Retrieving (SAFER) for estimating the evapotranspiration of two annual winter irrigated crops in the Cerrado (Brazilians Savannah) was evaluated. Multispectral and thermal images from the sensors ETM+/Landsat 7 and OLI-TIRS/Landsat 8 were used for this purpose. Initially, the model was calibrated for the wheat crop, then this calibration was tested for the bean crop, using Bowen ration ETa data as reference. After calibration, a coefficient of determination (r²) equal to 0.91 and the root mean square error (RMSE) equal to 0.58 mm d^-1 were found for the wheat. For the bean, the r² was equal to 0.65 and RMSE, equal to 0.77 mm d^-1. The results are satisfactory, although they suggest that the model may present an improved performance with specific calibration for each crop and/or region, or adopting calibration in two stages, for lower and higher NDVI values.