Isotopes in Land-surface Parameterisations : the IPILPS Proposal
A. Henderson-Sellers1, P. Aggarwal2, D. Noone3 and A. J. Pitman4
Approved “In Principle” by GLASS 27 August 2003
Aim
The land surface processes project within GEWEX, the GEWEX Land–Atmosphere System Study
(GLASS), aims to improve the representation of the energy and water fluxes and cycles in large scale
weather and climate models. Within GLASS, PILPS - the Project for Intercomparison of Land-surface
Parameterization Schemes - operates the off-line land-atmosphere intercomparisons. The aim of the
IPILPS initiative is to contribute to an international intercomparison of current state-of-the-art isotope
parameterization efforts in coupled climate, atmospheric and earth system models by promoting
comparison among land-surface schemes that incorporate isotopic representation under the auspices
of GLASS.
Motivation
Since the mid twentieth century the isotopic composition of water and carbon dioxide stored in
various archives (e.g. ice cores, ground water, biomass) has been recognized as being of value in the
study of changes in the atmosphere, hydrosphere and climate on timescales from glacial-interglacial
(Petit et al., 1999) to extreme weather variations (Lawrence & Gedzelman, 2003). Such changes in
local to global processes play a crucial role in forcing both past and future variability of the overall
Earth system.
The 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 among
which are the land-surface schemes employed in geophysical and biogeochemical models (e.g.
Henderson-Sellers et al., 2002). Isotopic data exist but, so far, there has been no tuning of models to
these data. However, as databases become more prevalent, schemes will be tested against, and
tuned to fit, isotopic measurements. There is therefore some urgency in establishing an international
intercomparison as soon as feasible.
Importance of the Land-surface
The continental surface is the locus of mankind’s habitation including dwellings, food production and
fresh water harvesting. Improving understanding & model predictive capability at the landatmosphere interface is a critically important goal of both WCRP (primarily through GLASS) and IGBP
(through the Integrated Land Ecosystem – Atmosphere Processes Study, ILEAPS). Measuring and
simulating the isotopic composition of water within the hydrological cycle of coupled, climate,
atmospheric and earth system models may help to overcome the deficit of observationally-validated
component simulations. Isotopic investigations of the 18O/16O and/or 2H/1H ratios demonstrated the
recycling of water in large river basins (Salati et al., 1979) and motivated the world’s first tropical
deforestation simulation (Henderson-Sellers & Gornitz, 1984). River routing parameterization
schemes may now be testable using river-based isotopic measurements being coordinated by the
International Atomic Energy Agency (e.g. Gibson et al., 2002).
The macroscopic interpretation of biophysical laws established at the molecular level is not unique
and as a consequence the land-surface simulation community will always be faced with a large
variety of models. These will differ in the scales that are explicitly represented and those which are
treated by conceptual representations of varying complexity. That intercomparison of off-line
simulations is of value in this diverse environment has been repeatedly demonstrated by
GLASS/PILPS – e.g. distributed hydrological applications (Lettenmaier and Bowling, 2002);
cryospheric simulation (e.g. Luo et al., 2003) and biological parameterization of carbon (e.g. Viovy,
2002).
Carbon isotopes are beginning to deliver value as measures of biogeochemical processes (e.g.
differentiating C3 and C4 photosynthesis). They can also be used to trace carbon flow through and
collection in various environmental pools (Riley et al., 2002). Importantly, carbon isotopes distinguish
IPILPS Proposal AH-S (August 2003)
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between terrestrial and oceanic fluxes of CO2 and can reveal details of soil decomposition, volatile
and dissolved organic compounds. Vegetation has been shown to affect the oxygen isotopic
composition of atmospheric CO2 (Farquhar et al., 1993).
Finally, many palaeoclimatic reconstructions interpreting changes in archived isotopic records in
terms of past conditions, especially temperature, fail to recognize the complexity of isotopic systems.
More complete interpretive methods based on derived global maps of past isotopic partitioning,
however, require detailed and valid parameterization of the surface-air interface (Dansgaard et al,.
1969, cf. Petit et al,. 1999).
Goals
It is timely to instigate a MIP focused on isotopic parameterization of the land-atmosphere interface.
IPILPS will build on the detailed knowledge and experience generated since the early 1990s in PILPS
(e.g. Pitman et al., 1999) and honed more recently within GLASS (e.g. Viovy, 2002) to contribute a
careful evaluation of land-surface schemes incorporating isotopes. The first initiative will focus on
stable isotopes of water and those of carbon. We plan a robust investigation of specific model
characteristics, or parameterizations, by comparing the results of several different land-surface
schemes run under identical boundary conditions.
Figure 1 Measurements of the isotopic concentration of oxygen 18 (18O) and deuterium (D) in water
vapour and precipitation at Belem, Brazil (1.43ºS, 48.48ºW). Daily isotopic concentrations are shown
as “delta” values where  is (R/Rstandard-1) x 1000.
Implementation Plan
There is a persuasive case for first examining three ‘typical’ environments: tropical forest, arid
grassland and a frozen soil/snow regime and three characteristic groups of land-surface schemes
IPILPS Proposal AH-S (August 2003)
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(Henderson-Sellers et al., 2003). This is because important isotopic characteristics differ significantly
in these situations: the tropical near-isothermal conditions allow probing of the Rayleigh formulation;
arid soils reveal ‘pulses’ of isotopically characterized water flows; and, as the solid phases of water do
not exchange isotopes with the atmosphere, snow & frozen soil water offer isotopically differentiable
characteristics in a strongly seasonal regime (Gibson & Edwards 2002).
We plan to test the proposed experimental framework using one (or two) LSSs incorporating
isotopes. Preliminary results from the first test experiments using one LSS, ISOLSM (Riley et al.,
2002) demonstrate that near-surface continental parameters of importance to the large-scale water
cycle are affected differently in different climate regimes (Figure 2).
Figure 2: Isotopic concentration of simulated water stores in ISOLSM. Results are spatial averages
over North America (45o-80oN), Siberia (45o-170oE, 45o-80oN), Equatorial Amazon (30oS-10oN) and
Australia. Isotopic concentrations are shown as “delta” values where  is (R/Rstandard-1)x1000 (after
Noone et al., 2003)
Two steps need to be completed before a general call for participation in this GLASS/PILPS MIP:
1. confirmation of the experimental plan; and
2. quality control of the available isotopic data (preferably new data not already used or
previously available to modelling groups).
Under the Global Network for Isotopes in Rivers (GNIR) initiative of the IAEA, Pradeep Aggarwal,
advises that the following novel data can be made available to GLASS: Amazon surface air vapour,
rivers, groundwater and precipitation – Figure 1.; Friedman et al. –USA Great Basin; Gibson et al. –
IPILPS Proposal AH-S (August 2003)
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Canadian Arctic; and Stone et al. - Murray Darling, Australia. Primary quality control of these data
will be undertaken by IAEA although it may be valuable to workshop (~3 days hosted by
IAEA/PILPS/GLASS) existing observational data in support of the IPILPS. This could involve a small
number of experts on biogeochemical isotope modelling (e.g. Inez Fung and David Schimmel),
oceans & ice core modellers (e.g. David Rind and Jean Jouzel) and hydrologists and/or climate
modellers interested in river basin water isotopes (e.g. Mike Bosilovich and Kit Szeto).
Timeline (draft)
1. August 2004: Approval by GLASS Panel
2. October/November 2004: Data availability and quality control confirmation
3. November/December 2004: Experimental framework agreement
4. January/February 2005: Call for participation to all current & past PILPS and AMIP II DSP 12
members
5. April/May 2005; First workshop and analysis
6. December 2005: Publication
Links
AMIP II – Diagnostic Subproject 12 (refer -Tom Phillips, PCMDI, LLNL)
SIMPLE: “Stable Water Isotope Modelling Intercomparison Initiative” (refer - Martin Werner, MPI,
Jena)
CCSM: new isotope working group initiative (refer - Natalie Mahowald, ACD, NCAR)
Global Network for Isotopes in Rivers (GNIR) initiative (refer - Pradeep Aggarwal, IAEA).
References
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climates – better skill or moving targets?, Geophys. Res Lett. 30, (14), 1777,
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Lawrence, J.R. and Gedzelman, S.D. (2003) Tropical ice core isotopes: do they reflect changes in
storm activity. Geophys. Res. Lett., 30, No.2, 44-1 to 44-4, 10.1029/2002GL015906
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Gedney, N., Gusev, Y.M., Habets, F., Kim, J., Kowalczyk, E., Mitchell, K., Nasonova, O.N., Noilhan,
J., Pitman, A.J., Schaake, J., Shmakin, A.B., Smirnova, T.G., Verseghy, D., Wetzel, P., Xue, Y.,
Yang, Z.-L. and Zeng, Q.C., 2003, Effects of frozen soil on soil temperature, spring infiltration, and
runoff: results from the PILPS 2(d) experiment at Valdai, Russia, J. Hydrometeorology, 4, 334-351
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core, Antarctica, Nature, 399, 429–436
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World Meteorological Organization, 4.19-4.20
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Viovy,
N.,
2002,
Description
of
the
tokyo.ac.jp/GLASS/Doc/2002/pilpsc1-galss.pdf
PILPS
C-1
experiment,
http://hydro.iis.u-
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Contact
Ann Henderson-Sellers, ANSTO Environment
Currently Visiting NCAR CGD and CIRES / NSIDC, Boulder, Colorado, USA
[email protected]
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Sponsors
Pradeep Aggarwal, Isotope Hydrology Section, International Atomic Energy Agency, Vienna, Austria
[email protected]
David Noone
Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
Andrew Pitman
Integrated Land Ecosystem – Atmosphere Processes Study (ILEAPS) member,
Professor of Physical Geography, Macquarie University, North Ryde, Australia
IPILPS Proposal AH-S (August 2003)
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