Linking evapotranspiration, boundary-layer processes and atmospheric moisture using isotope tracer modeling and data

This study uses high-quality spectroscopy measurements to place local constraints on the isotopic composition of near-surface water vapor in an isotope-incorporated land surface model. A full-year, near continuous observation of hourly oxygen-18 and deuterium isotope ratios in atmospheric water vapor at Wind River field station, WA, USA, reveals times of strong influence from surface ET versus times when convective mixing dominates. These surface isotope measurements provide a robust foundation to improve the representation of the kinetic isotopic effects arising from ET and source water partitioning. Nudged, isotope-enabled GCM (IsoGSM) simulations reproduce isotopic variations influenced by large-scale, synoptic weather cycles, but are less successful in capturing variations associated with sub-grid processes. Specifically, the model is unable to produce the large and consistent variability in the deuterium excess (dx) values of near-surface water vapor. This ‘terrestrial feedback’ to...