2.3.2 D-excess
Deuterium excess (hereafter D-excess, d ) is understood as a measure of the deviation of the LMWL from the GMWL. D-excess is also a key parameter to infer the origin of atmospheric vapor regarding the evaporation conditions in the region source of precipitation (Petit, White, Young, Jouzel, & Korotkevich, 1991; Froehlich, Gibson, & Aggarwal, 2002; Froehlich et al., 2008). D-excess follows the relationship:
d = δ2H − 8δ18O. (2)
Higher values of d refer to moisture originated under conditions of lower relative humidity, where the kinetic fractionation is more pronounced. Lower values of d correspond to air masses where the fractionation was close to equilibrium (Clark & Fritz, 1999). However, some secondary processes can change the initial value. For instance,d is an indicator of moisture recycling as evaporation from the land surface to the atmosphere increases its value (Froehlich et al., 2002; Froehlich et al., 2008). Spatial reconstruction of d values was developed through coKriging interpolation, using precipitation and temperature as auxiliary variables for improving the estimations over areas where there is no sampling data. The spatial resolution of D-excess value in the study zone is 1°x1° degree.