Preprints
https://doi.org/10.5194/hess-2020-519
https://doi.org/10.5194/hess-2020-519

  20 Oct 2020

20 Oct 2020

Review status: this preprint is currently under review for the journal HESS.

New isotope-based evapotranspiration partitioning method using the Keeling plot slope and direct measured parameters

Yusen Yuan1,2, Lixin Wang2, Wenqing Lin1, Wenzhe Jiao2, and Taisheng Du1 Yusen Yuan et al.
  • 1Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China
  • 2Department of Earth Sciences, Indiana University–Purdue University Indianapolis, Indianapolis, Indiana 46202, USA

Abstract. To better quantify water and energy cycles, numerous efforts to partition evapotranspiration (ET) into evaporation (E) and transpiration (T) have been made over the recent half century. Various methods such as direct measurements, analytical models and satellite-based estimations have been used to separate ET across the field scale to the global scale. One of the analytical methods, isotopic approach, has been often applied in terrestrial ecosystem ET partitioning. The isotopic composition of ET (δET) is a crucial parameter in the traditional isotope-based ET partition model, which however has considerable uncertainty. Here we proposed a new method relying on Keeling plot slope (k), and relying on the direct measurements of atmospheric vapor concentration (Cv) and isotopic composition of atmospheric vapor (δv), to avoid the direct use of δET. Mathematical derivation of the new method was provided, and field observations were used to evaluate the new method. The T/ET results based on the new method agreed well with those using the traditional isotopic method. The new method eliminates the high sensitivity contribution parameter δET. In addition, the new method utilized directly measured values and regressive slope of Keeling plot instead of using the interpolated Keeling plot intercept. Our study shows an analytical framework to estimate T/ET based on the Keeling plot slope and direct-measured parameters. The new method potentially reduces the uncertainty of isotope-based ET partition approach.

Yusen Yuan et al.

 
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Yusen Yuan et al.

Yusen Yuan et al.

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