An Application of the Keeling Plot Slopes: New Isotope-Based Evapotranspiration Partition Method

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 field scale to global scale. Isotopic approach has been widely used in terrestrial ecosystem ET partition. The isotopic composition of ET (δ_ET) is a crucial parameter in traditional isotope-based ET partition model, which however has large uncertainty. Here we put forward a new method relying on the slope of Keeling plot (k) to avoid the direct use of δ_ET. Derivation of the new method was provided, and observation data was used to evaluate the new method. Result showed that a regression analysis between the novel method and traditional isotopic method was highly significant. The sensitivity of k in the novel method was lower than that of δ_ET in the traditional model. This study provides an analytical framework to estimate T/ET using a novel method and provide an insight into the numerical relationship between Keeling plot slope and T/ET.

Key words: evapotranspiration, Keeling plot slope, transpiration, stable isotope