Résumé
Evapotranspiration (ET) is a key variable in the understanding of the hydrological cycle. However, in many regions, like the Sahelian Regions, there is a spatial scarcity of in-situ ET measurements, in spite of its vulnerability to water availability and food security problems. However, in the past decade, many spatialized ET products have been released. They use various calculation methods like physical or empirical modelling, upscaling of in-situ measurements or data fusion approaches. The aim of this study is to propose a quite exhaustive review and evaluation of global or continental ET products available over typical Sahelian ecosystems in both Senegal and Niger, in the frame of the EVAP’EAU project (ICIREWARD Unesco Center). 20 ET products have thus been evaluated at local scale, using flux tower measurements over a typical agropastoral ecosystems. A meso-scale (~150km) evaluation has also been performed, by doing a cross comparison of the products at different spatial aggregation levels. Results show that the products with the best temporal representation of ET have the lowest spatial resolution (>10km), and thus lack of spatial representativeness. On the other hand, higher resolution products (<1km) show a realistic spatial distribution but several issues on the representation of the ET cycle seasonality. Therefore, in order to tackle water and agricultural management issues, there is need for better spatialized ET estimates at both high spatial and temporal resolution in Sahelian region. This could be achieved by proposing new data fusion methods, dedicated to these issues. However, the upcoming TRISHNA (CNES-ISRO), LSTM (ESA) and SBG (NASA) satellite missions will help to fill this gap by providing TIR data and products with high spatial (~50m) and temporal (~2 days) resolution.