Stable water isotopes: revolutionary tools for global water cycle disturbance diagnosis

Here we assess the simulation of isotopic fluxes in basin-scale hydrology, focusing on the 'big leaf' representation of land surfaces in numerical models as the current mechanism for incorporating water isotopes. Applications of the simulation of stable isotopic behaviour simulated by global climate or earth system models, including river isotopic characterization of basin changes and plant-respired oxygen isotope 'tagging', to resolving uncertainty are limited until more basic criteria such as conservation, current mean climate and capture of observed variability are demonstrated. We find that surface water budgets are still rather poorly simulated and inadequately constrained at the scale of large basins; yet surface energy partition can be apparently well captured by models with inadequate land-surface parameterization. (author)