HR: 11:50h
AN: B41E-07    [PDF]
TI: Incorporating and Evaluating Stable Water Isotopes into Land-surface Parameterisation Schemes
AU: * Henderson-Sellers, A
EM: ahssec@ansto.gov.au
AF: ANSTO Environment, PMB 1, Menai, NSW 2234 Australia
AU: McGuffie, K
EM: kendal.mcguffie@uts.edu.au
AF: Department of Applied Physics, University of Technology, Sydney, Broadway, NSW 2007 Australia
AB: Measuring and simulating the isotopic composition of water in the near-surface component of the hydrological budget of coupled climate system models may help to overcome the lack of observational data for validation. Isotopic investigations (Salati {\it et al.}, 1979) of the $^{18}$O/$^{16}$O and $^2$H/$^1$H ratios motivated the world's first global climate model tropical deforestation simulation (Henderson-Sellers and Gornitz, 1984). The GRDC (Global Runoff Data Centre) runoff data set is problematic as a source for model validation in some areas (e.g. Amazon) because it is inconsistent with accepted precipitation data such as CMAP. However, modelled river routing systems are now being tested against river-based isotopic measurements (e.g. Gibson {\it et al.}, 2002). Complete interpretation of isotopic variations in terms of system variability and change is currently handicapped by the lack of agreed and validated isotopic earth system model components, although this difficulty is balanced by the fact that there has been no tuning of models to isotopic data as yet. Before databases become more prevalent and schemes are tested against, and tuned to fit, isotopic measurements, this initiative contributes an intercomparison of current state-of the-art isotope modelling. Among the land-surface schemes that incorporate isotopic representation that were compared under the auspices of IPILPS (Isotopes in the Project for Intercomparison of Land-surface Parameterization Schemes) we find three characteristic groups (Henderson-Sellers {\it et al.}, 2003). Results from experiments using ISOLSM (Riley {\it et al.}, 2002) demonstrate that the near-surface isotopic composition of the atmosphere is affected differently in different climate regimes. Our results make a persuasive case for examining other environments in which isotopic characteristics differ significantly, e.g. the tropical forests where near-isothermal conditions allow probing of the Rayleigh formulation; arid soil revealing \lq pulses' of isotopically characterized water flows; and, as the solid phases of water do not exchange isotopes with the atmosphere, snow and frozen soil water, which isotopically differentiate characteristics seasonally (Gibson \& Edwards 2002).
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
SC: Biogeosciences [B]
MN: 2003 Fall Meeting