Iso-MATSIRO, a land surface model that incorporates stable water isotopes

This paper describes Iso-MATSIRO, a land surface model that includes stable water isotopes and simulates physically reasonable isotopic fluxes and reservoirs at the ground. The model calculates kinetic and equilibrium fractionation of HDO and H218O between ice, liquid, and vapor phases and separately considers soil surface evaporation, vegetation transpiration, evaporation from the canopy-intercepted reservoir, and snow sublimation. New aspects are consideration of subsurface advective flow and the use of canopy resolved leaf water. One-dimensional simulations with modeled meteorological forcings showed reasonable features in the annual isotopic budget, seasonal variations of δ18O in soil moisture, diurnal variations of leaf water with some enrichment, and δ-diagram of representative surface reservoirs and fluxes. Kinetic fractionation, however, should be carefully parameterized. A subsequent, independent global simulation used Iso-MATSIRO coupled with an atmospheric isotope circulation model for a half year in 1998. Simulated precipitation δ18O was closer to observations than in a previous study, confirming the physical treatments of isotopes in the land surface processes, and indicating their large impact on precipitation isotopes over middle to high latitudinal continents.