Upscaling instantaneous to daily evapotranspiration (ETi
) is one of the central challenge in regional vegetation water use mapping using polar orbiting satellites. Here we developed a robust ETi
upscaling for global studies using the ratio between daily and instantaneous global radiation (RSd
). Using data from 126 FLUXNET tower sites this study demonstrated RSd
ratio to be the most robust factor explaining ETd
variability across variable sky conditions and multiple biomes.