ISBA ModelISBA and TEB Code (and stand-alone DRIVER) in FORTRAN90
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Case Studies available for Model Validation
(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.
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.
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.  Back
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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.
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.
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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A more
thorough description of
ISBA-Ags can be found