Main description :

The new ISBA-CTRIP global land surface modeling system is more ambitious than the previous version, ISBA-TRIP. This system developed during the last decade is embedded in the SURFEX version 8 modeling platform. It is used in our atmospheric climate models and our coupled climate models that participate in CMIP6 but also in large scale hydrological applications. ISBA via SURFEX and CTRIP are interfaced with the Xml configurable Input/Output Server (XIOS) developped by IPSL/LSCE in order to provide both high performance output for massively parallel simulations, an easy configuration of model outputs and of some inline post-processing.

ISBA-CTRIP can be used with its physical core only, as for instance in our CNRM-CM6-1 climate model. It can also be used with the carbon cycle activated as in our « Earth System » model CNRM-ESM2-1.

 Physical core :

Schematic representation of the ISBA-CTRIP hydrologic modelling system used for climate and hydrological applications at the global scale (following Decharme et al. 2019).

ISBA is used here in its multi-layer "diffusion" version. It explicitly solves the one-dimensional Fourier and Darcy laws throughout the soil (Boone et al. 2000; Decharme et al. 2011; Decharme et al. 2013), accounting for the hydraulic and thermal properties of soil organic carbon (Decharme et al. 2016). The use of a multilayer snow model of intermediate complexity (Boone and Etchevers 2001; Decharme et al. 2016) allows separate water and energy budgets to be simulated for the soil and the snowpack. The leaf area index is imposed from satellite observations (as it is the case in CNRM-CM6-1) but, for some studies, it can also be interactively calculated (optional) as in the « Earth System » version.

CTRIP simulates river discharges and means "the CNRM version of TRIP". Indeed, the previous TRIP was coded in Fortran 77 with binary I/O format, which limited its performance, the development of new physical components, and its ability to be coupled with others models. Accordingly, it has been re-coded in Fortran 90 using the netcdf I/O format, and the previous global river channel network at 1° resolution has been increased to 0.5° resolution and enhanced over Europe. The river stream flow velocity is now solved dynamically via Manning’s formula and assuming a rectangular river cross-section (Decharme et al. 2010).

An explicit two-way coupling between ISBA and CTRIP has been set up via the introduction of a standardized coupling interface in SURFEX (Voldoire et al. 2017) with the OASIS3-MCT coupler. This coupling accounts for, first, a dynamic river flooding scheme in which floodplains interact with the soil and the atmosphere through free-water evaporation, infiltration and precipitation interception (Decharme et al. 2012) and second, a two-dimensional diffusive groundwater scheme to represent unconfined aquifers and upward capillarity fluxes into the superficial soil (Vergnes et al. 2012; Vergnes and Decharme 2012; Vergnes et al. 2014).

More details on hydrological aspects can be found in Decharme et al. 2019.

  Earth system :

Schematic of the carbon fluxes simulated by the ISBA-CTRIP "Earth System" version using 19 different surface types: 16 types of vegetation, bare ground, ice and rock. Following Delire et al. (2019).

The « Earth system » version of ISBA-CTRIP has a full representation of the land carbon cycle. The land biogeochemical module in ISBA represents plant physiology (photosynthesis and autotrophic respiration), carbon allocation and turnover, and carbon cycling through litter and soil. It also includes a module for wild fires, land cover changes, and carbon leaching through the soil. This dissolved organic carbon (DOC) is then transported to the ocean via the CTRIP hydrographic network.

Leaf photosynthesis is represented by the semi-empirical model proposed by Goudriaan et al. (1985), and implemented by Calvet et al (1998). Canopy level assimilation is calculated using a 10-layer radiative transfert scheme including direct ans diffuse radiation (Carrer et al. 2013). Vegetation in ISBA is represented by 4 carbon pools for grasses and crops (leaves, stem, small non structural carbonhydrate-NSC-storage pool, roots) and 6 for trees (leaves, twigs, aboveground wood, NSC storage, fine and coarse roots) (Gibelin 2007; Joetzjer et al. 2015). Leaf phenology results directly from the carbon balance of the leaves (Calvet and Soussana 2001). The model distinguishes 16 vegetation types (9 tree and 1 shrub types, 3 grass types and 3 crop types) alongside desert, rocks and permanent snow.

The litter and soil organic matter module in ISBA (Gibelin. 2007) is based on the soil carbon part of the CENTURY model (Parton et al. 1988). The 4 litter and 3 soil carbon pools are defined based on their presumed chemical composition, their location above- or below-ground and potential decomposition rates (or turnover times). The litter pools are supplied by the flux of dead biomass from each biomass reservoir (turnover). Decomposition of litter and soil carbon releases CO2 (heterotrophic respiration). During the decomposition process, some carbon is dissolved by water slowly percolating through the soil column. This dissolved organic carbon is transported by the rivers to the ocean by CTRIP.

In order to represent past and future climate evolution ISBA-CTRIP needs to take into account land cover changes that affect energy and water exchanges but also CO2. The changing geographical distribution of plant types was introduced in ISBA-CTRIP and allows to use the maps of land cover changes developped for IPCC simulation exercises for instance.

A detailed description of the terrestrial carbon cycle can be found in Delire et al. (2019).

  Publications :


  • Decharme B., Delire C., Minvielle M., Colin J., Vergnes J.-P., Alias A., Saint-Martin D., Séférian R., Sénési S., Voldoire A., (2019). Recent changes in the ISBA‐CTRIP land surface system for use in the CNRM‐CM6 climate model and in global off‐line hydrological applications. Journal of Advances in Modeling Earth Systems, 11, 1207– 1252.,
  • Delire C., Séférian R., Decharme B., Alkama R., Calvet J.‐C., Carrer D., Gibelin A.-L., Joetzjer E., Morel X., Rocher M., Tzanos D. (2020). The global land carbon cycle simulated with ISBA‐CTRIP: Improvements over the last decade. Journal of Advances in Modeling Earth Systems, 12, e2019MS001886.
  • Voldoire, A., Decharme, B., Pianezze, J., Lebeaupin Brossier, C., Sevault, F., Seyfried, L., et al. (2017). SURFEX v8.0 interface with OASIS3-MCT to couple atmosphere with hydrology, ocean, waves and sea-ice models, from coastal to global scales. Geoscientific Model Development, 10(11).

ISBA "diffusion" :

  • Boone, A., Masson, V., Meyers, T., Noilhan, J., Boone, A., Masson, V., et al. (2000). The Influence of the Inclusion of Soil Freezing on Simulations by a Soil–Vegetation–Atmosphere Transfer Scheme. Journal of Applied Meteorology, 39(9), 1544–1569.<1544:TIOTIO>2.0.CO;2
  • Decharme, B., Boone, A., Delire, C., & Noilhan, J. (2011). Local evaluation of the Interaction between Soil Biosphere Atmosphere soil multilayer diffusion scheme using four pedotransfer functions. Journal of Geophysical Research Atmospheres, 116(20).
  • Decharme, B., Martin, E., & Faroux, S. (2013). Reconciling soil thermal and hydrological lower boundary conditions in land surface models. Journal of Geophysical Research Atmospheres, 118(14).
  • Decharme, B., Brun, E., Boone, A., Delire, C., Le Moigne, P., & Morin, S. (2016). Impacts of snow and organic soils parameterization on northern Eurasian soil temperature profiles simulated by the ISBA land surface model. Cryosphere, 10(2).

ISBA "carbon" :

  • Calvet, J.-C., Noilhan, J., Roujean, J.-L. L., Bessemoulin, P., Cabelguenne, M., Olioso, A., & Wigneron, J.-P. P. (1998). An interactive vegetation SVAT model tested against data from six contrasting sites. Agricultural and Forest Meteorology, 92(2), 73–95.
  • Calvet, J. C., Soussana J., F. (2001), Modelling CO2-enrichment effects using an interactive vegetation SVAT scheme, Agr. Forest Meteol., 108,129-152.
  • Carrer, D, Roujean, J.-L., Lafont, S., Calvet, J.-C., Boone, A., Decharme, B., Delire, C., and Gastellu-Etchegorry, J. P. (2013), A canopy radiative transfer scheme with explicit FAPAR for the interactive vegetation model ISBA-A-gs: impact on carbon fluxes, J. Geophys. Res. Biogeo., 118, 1–16, doi:10.1002/jgrg.20070.
  • Gibelin 2007, Cycle du carbone dans un modèle de surface continentale : modélisation, validation et mise en oeuvre à l’échelle globale, thèse de doctorat, 2007
  • Goudriaan, J., H.H. van Laar, H. van Keulen & W. Louwerse: Photosynthesis, C0 2 and plant production. In: W. Day & R.K. Atkin (Eds.), Wheat growth and modelling. NATO AS/ Series, Series A, Vol 86. Plenum Press, New York, 107-122. 1985
  • Joetzjer E., Delire C., Douville H., Ciais P., Decharme B., D. Carrer, H. Verbeeck, M. De Weirdt, D. Bonal (2015), Improving the ISBACC land surface model simulation of water and carbon fluxes and stocks over the Amazon forest, Geosci. Model Dev. 8, 1709-1727, doi:10.5194/gmd-8-1709-2015
  • Parton, W. J., Stewart, J. W. B., & Cole, C. V. (1988). Dynamics of C, N, P and S in grassland soils: a model. Biogeochemistry, 5(1), 109–131.


  • Decharme, B., Douville, H., Prigent, C., Papa, F., & Aires, F. (2008). A new river flooding scheme for global climate applications : Off-line evaluation over South America. Journal of Geophysical Research Atmospheres, 113(11).
  • Decharme, B., Alkama, R., Douville, H., Becker, M., & Cazenave, A. (2010). Global Evaluation of the ISBA-TRIP Continental Hydrological System. Part II: Uncertainties in River Routing Simulation Related to Flow Velocity and Groundwater Storage. Journal of Hydrometeorology, 11(3), 601–617.
  • Decharme, B., Alkama, R., Papa, F., Faroux, S., Douville, H., & Prigent, C. (2012). Global off-line evaluation of the ISBA-TRIP flood model. Climate Dynamics, 38(7–8), 1389–1412.
  • Vergnes, J.-P., & Decharme, B. (2012). A simple groundwater scheme in the TRIP river routing model: Global off-line evaluation against GRACE terrestrial water storage estimates and observed river discharges. Hydrology and Earth System Sciences, 16(10).
  • Vergnes, J.-P., Decharme, B., Alkama, R., Martin, E., Habets, F., & Douville, H. (2012). A simple groundwater scheme for hydrological and climate applications: Description and offline evaluation over France. Journal of Hydrometeorology, 13(4).
  • Vergnes, J.-P., Decharme, B., & Habets, F. (2014). Introduction of groundwater capillary rises using subgrid spatial variability of topography into the ISBA land surface model. Journal of Geophysical Research, 119(19), 11,065-11,086.