Comparative Assessment of Different Satellite-Derived Actual Evapotranspiration Estimates in Northeast Italy

Accurate estimation of actual evapotranspiration (ETa) is essential for understanding hydrological processes and managing water resources, especially in regions characterized by intensive agriculture and complex groundwater–surface interactions. This study intercompares three independent satellite-based ETa estimation approaches applied over Northeast Italy. The first two methods correspond to the classical MODIS algorithm (MOD16), which is based on a simplified Penman–Monteith approach, and to the more recent Sen-ET modelling framework, which relies on a surface energy balance principle. The outputs of these methods are compared to those produced by a water balance algorithm, NDVI-Cws, which predicts ETa through the combination of conventional ancillary data and MODIS NDVI imagery. The results obtained show that, while the MODIS algorithm yields ETa estimates which are generally lower than those of Sen-ET and NDVI-Cws, the latter methods produce similar predictions for most cover types examined. The same two methods are potentially capable of providing higher spatial resolution daily ETa estimates depending on the satellite inputs used; out of them, however, only NDVI-Cws can yield spatially complete and temporally continuous datasets. The analysis therefore provides insights into the reliability and usability of different remote sensing approaches for regional-scale water resource monitoring.