ISBA Model

ISBA and TEB Code (and stand-alone DRIVER) in FORTRAN90

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Case Studies available for Model Validation

ISBA Standard

(Noilhan and Planton 1989: Noilhan and Mahfouf 1996

   A parameterization of land surface processes to be included in mesoscale and large-scale meteorological models is presented. The number of parameters has been rcduced as much as possible, while attempting to preserve the representation of the physics which controls the energy and water budgets. We distinguish two main classes of parameters. The spatial distribution of primary parameters, i.e., the dominant types of soil and vegetation within each grid cell, can be specified from existing global datasets. The secondary parameters, describing the phyisical properties of each type of soil and vegetation, can be inferred from measurements or derived from numerical experiments. A single surface temperature is used to nt the surface energy balance of the land/cover system. The soil heat flux is linearly interpolated between its value over bare ground and a value of zero for complete shielding of the vegetation. The ground surface moisture equation includes the effect of gravity and the thermo-hydric coefficients of the equations have been either calculated or calibrated using textural dependent formulations. The calibration has been made using the results of a detailed soil model forced by prescribed atmospheric mean conditions. The results show that the coefficients of tlte surface soil moisture equation are greatly dependent upon the textural class of the soil as well as upon its moisture content. The new scheme has been included in a one-dimensional model which allows a complete interaction between the surface and the atmosphere. Several simulations have been performed using data collected during HAPEX-MOBILHY. These first results show the ability of the parameterization to reproduce the components of the surface energy balance over a wide variety of surface conditions.
Schematic diagrams of the baseline scheme. The mass (water) and heat transfer pathways and reservoirs/stores are indicated. 

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(Calvet et al. 1998

   The soil-vegetation-atmosphere transfer (SVAT) schemes now employed in meteorology are at the surface together with the water partitionning between vegetation transpiration, drainage, surface runoff and soil moisture change. Recent advances in SVAT modeling consisted in accounting for vegetation- climate-CO2 feedbacks in order to:

(1) describe, in a more realistic way, the canopy stomatal conductance by considering the functional relationship between stomatal aperture and photosynthesis (Wong et al. 1979)

(2) make the SVATs more general in order to properly simulate the surface processes in contrasting CO2 concentration, air temperature, and air humidity conditions, with the same calibrated model

(3) use the estimated assimilation rate to simulate the plant growth and mortality, and diagnose the leaf area index (LAI) consistently with the prescribed climate and CO2 concentration (Calvet et al. 1998).

   The ISBA (Interactions between Soil, Biosphere, and Atmosphere) scheme (Noilhan and Planton 1989) was modified in order to account for the atmospheric carbon dioxide concentration on the stomatal aperture. The physiological stomatal resistance scheme proposed by Jacobs (1994) was employed to describe photosynthesis and its coupling with stomatal resistance at leaf level. In addition, the plant response to soil water stress was accounted for by a normalized soil moisture factor applied to the mesophyll conductance. The computed vegetation net assimilation was used to feed a simple growth submodel, and to predict the density of vegetation cover. Only two parameters are needed to calibrate the growth model: the leaf life expectancy and the effective biomass per unit leaf area. The new scheme, called ISBA-Ags, was tested against data from six micrometeorological databases for vegetation ranging from temperate grassland to tropical forest.
A more thorough description of ISBA-Ags can be found here

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Sub-grid Surface Runoff Scheme

(Habets et al. 1999a

   As a first step towards coupling atmospheric and hydrological models, this article describes the implementation of the Interactions between the Soil Biosphere Atmosphere (ISBA) surface scheme within a macroscale hydrological model at the regional scale. The introduction of the diurnal cycle in the hydrological model allows a coupling with the atmosphere through the energy balance and water budget computations. The coupled model is used in a forced mode, i.e. atmospheric forcing is imposed on the surface scheme without any retroaction of the surface exchanges on the atmosphere. The initial version of ISBA was modified to account for sub-grid runoff. Existing classifications of soil and vegetation at high spatial resolution (1 km) were used in conjunction with satellite information to monitor the monthly evolution of the vegetation. A dense surface network facilitated the interpolation of atmospheric fields with a time step of 3 h. The two years considered show large differences of annual precipitation and potential evaporation, which have an impact on the regime of the river flows. A one-dimensional study presents the sensitivity of the partitioning of precipitation into evaporation and runoff to the sub-grid runoff and drainage parameterizations, soil depth, and vegetation cover.

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ISBA 3-Layer Soil Hydrological Model

(Boone et al. 1998

   The inclusion of a third soil layer in the Interactions between the Soil Biosphere and Atmosphere (ISBA) model is presented in this paper. The soil water content between the base of the root zone and the deep soil layer is described using a generalized form of the force-restore method. The new force restore coefficient is calibrated using a detailed high-resolution soil water transfer model, and it is then related to the soil textural properties using simple regression relationships. It is shown that the use of a calibrated coefficient gives better results, in general, than a direct solution method using similar model geometry with the same number of layers.

   In the initial two-layer version of ISBA, it was not possible to distinguish the root zone and sub-root zone soil water reservoirs. With the three-layer version, the deep soil layer may provide water to the system through capillary rises only, and the available water content (for transpiration) is clearly defined. Three test cases are examined in which atmospheric forcing, a good description of the soil properties and vegetation cover and measured soil moisture profile data are present for an annual cycle. Using the three-layer version of ISBA, there is general improvement in modeling results, and values for key parameters which relate evapotranspiration to soil moisture are more consistent with those inferred from observations.
Schematic diagrams of the baseline 2-layer and new 3-layer schemes. The mass (water) pathways and reservoirs are indicated. 

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ISBA-ES: 3-Layer Snow Model

(Boone and Etchevers 2000

    There are currently two ISBA snow scheme options available for hydrological modeling: the baseline force-restore approach which uses a composite snow-soil-vegetation energy budget and a single snow layer, and a multi-layer detailed internal process snow model. The force-restore method is currently used in atmospheric modeling applications (Meteo-France GCM: ARPEGE). Recent studies have shown that hydrological simulations for mountainous catchments within the Rhone basin, France, are significantly improved using the detailed snow scheme. The main drawback is that the scheme is computationally expensive and it is not currently feasible for routine application in atmospheric models. For these reasons, a third new intermediate complexity scheme has been developed which includes certain key physical processes from the complex model for improved snowpack realism and hydrology while it attempts to have computational requirements similar to the simple default scheme. The new scheme has been evaluated and compared with the results from the two other schemes at a local scale at an alpine site located within the Rhone basin for two contrasting (weather) years. It has been tested using the PILPS-Valdai experimental design and dataset. It has recently been used in the PILPS Phase2e intercomparison study, the Rhone-AGGregation land surface scheme intercomparison project, and it is participating in the SNOWMIP project. 
A Meteo-France Technical Memo (Note de Centre) which describes ISBA-ES in detail is available on request (
Schematic diagrams of the the mass (water) and energy pathways and reservoirs for ISBA-ES. 

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Case Studies for Model Validation/Testing

The case studies currently available for use by ISBA or other Soil Vegetation Atmosphere Transfer (SVAT) schemes for validation/testing are listed below. A breif description of each dataset and associated published references will be added soon. Please contact us about data availability.

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