Water stress occurs when the demand for water exceeds the available amount during a certain period or when poor quality restricts its use. Water stress causes deterioration of fresh water resources in terms of quantity (aquifer over-exploitation, dry rivers, etc.) and quality (eutrophication, organic matter pollution, saline intrusion, etc.). Water stress and evapotranspiration estimated through the residual and contextual methods are instantaneous values at the time of the satellite overpass. The reconstruction of daily or seasonal evapotranspiration therefore requires the use of extrapolation (reconstitution of the diurnal cycle) and interpolation (estimation between two successive images, methods. Apart from the assimilation methods mentioned above, which allow us to continuously simulate AET over time according to the water supply forcing data but are relatively complex to implement, different simple reconstitution methods of temporal variations of AET are proposed. Water stress or an equivalent variable such as the evaporative fraction EF (the ratio between latent heat flux and available energy Rn-G), have the advantage of being dimensionless and relatively stable during the day, and are therefore good candidates for these reconstruction techniques. The evaporative fraction is relatively constant around the solar noon, especially during periods of water stress.