Determining the contribution of transpiration to the surface moisture fluxes – a perspective on different approaches

Continental evaporation (including transpiration, soil evaporation and interception) is an important process controlling energy and mass exchange between the terrestrial ecosystems and the atmosphere. Current techniques to disentangle the total evaporative flux into a contribution evaporated from soils, or transpired by plants are under debate. Many isotope-based studies show that transpiration contributes generally more than 70% to the total moisture fluxes while other isotope-independent techniques lead to transpiration fractions less than 70%. This paper provides a perspective on isotope based versus non-isotope based partitioning studies. We suggest that future studies should validate the parameterization of land surface and climate models by comparing the computed water isotope signals in the atmosphere with the available remote sensing and flux-based data sets to provide a better understanding of the hydrological cycle in vegetated regions.