Abstract
Abstract. Current techniques to disentangle the evaporative fluxes from the continental surface into a contribution evaporated from soils and canopy, or transpired by plants, are under debate. Many isotope-based studies show that transpiration contributes generally more than 70% to the total evaporation, while other isotope-independent techniques lead to considerably smaller transpiration fractions. This paper provides a perspective on isotope-based versus non-isotope-based partitioning studies. Some partitioning results from isotope-based methods, hydrometric measurements, and modeling are presented for comparison. Moreover, the methodological aspects of the partitioning analysis are considered, including their limitations, and explanations of possible discrepancies between the methods are discussed. We suggest sources of systematic error that may lead to biases in the results, e.g., instruments inaccuracy, assumptions used in analyses, and calibration parameters. A number of comparison studies using isotope-based methods and hydrometric measurements in the same plants and climatic conditions are consistent within the errors; however, models tend to produce lower transpiration fractions. The relatively low transpiration fraction in current state-of-the-art land-surface models calls for a reassessment of the skill of the underlying model parameterizations. The scarcity of global evaporation data makes calibration and validation of global isotope-independent and isotope-based results difficult. However, isotope-enabled land-surface and global climate modeling studies allow for the evaluation of the parameterization of land-surface models by comparing the computed water isotopologue signals in the atmosphere with the available remote sensing and flux-based data sets. Future studies that allow for this evaluation could provide a better understanding of the hydrological cycle in vegetated regions.
Highlights
IntroductionContinental evaporation (including transpiration, soil evaporation, and canopy evaporation) is an important process controlling energy and mass exchange between the terrestrialS
Continental evaporation is an important process controlling energy and mass exchange between the terrestrialPublished by Copernicus Publications on behalf of the European Geosciences Union.S
Many isotope-based studies show that transpiration contributes generally more than 70 % to the total evaporation, while other isotope-independent techniques lead to considerably smaller transpiration fractions
Summary
Continental evaporation (including transpiration, soil evaporation, and canopy evaporation) is an important process controlling energy and mass exchange between the terrestrialS. Many studies have been carried out to quantify the transpiration fraction through direct measurements or techniques disentangling the various evaporation components. Direct measurement of transpiration has been performed for decades, but the accuracy and separation of transpiration from total evaporation still remain a challenge. The fraction of transpiration to the total evaporation flux obviously depends upon the nature and state-of-the-surface, such as the presence of lakes or the seasonality of vegetation (growing in the spring or dormant in autumn). These conditions generate variability in each evaporation component and complicate the separation of the various components
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