(1) MODEL AND VERSION
Full model name: CARAIB (CARbon Assimilation In the Biosphere)
Host institution: LPAP (Laboratory for Planetary and Atmospheric Physics)
Key references:
François L., B. Nemry, P. Warnant and J.-C. Gérard; Seasonal and Interannual Influences of the Terrestrial Ecosystems on Atmospheric CO2: a
Model Study. Phys. Chem. Earth, 21, 537-544, 1996.
François L., Ch; Delire, P. Warnant and G. Munhoven. Modelling the glacial-interglacial changes in the continental biosphere. Global and Planetary Change, 16-17, 37-52, 1998.
Gérard J.-C., B. Nemry, L.M. François and P. Warnant. The interannual change of atmospheric CO2: contribution of subtropical ecosystems ? J. Geophys. Res., 26, 243-246, 1999.
Hubert B., L. François, P. Warnant and D. Strivay. Stochastic generation of meteorologic variables and effects on global models of water and carbon cycles in vegetation and soils. J. of Hydr., 212-213, 318-334, 1998.
Nemry B., L. François, P. Warnant, F. Robinet and J.-C. Gérard. The seasonality of the CO2 exchange between the atmosphere and the land biosphere: a study with a global mechanistic vegetation model. J. Geophys. Res., 101, 7111-7125, 1996.
Nemry B., L. François, J.-C. Gérard, A. Bondeau and M. Heimann. Comparing global models of terrestrial net primary productivity (NPP): analysis of the seasonal atmospheric CO2 signal. Global Change Biology, 5 (suppl. 1), 65-76, 1999.
Warnant P., L. François, D. Strivay and J.-C. Gérard. CARAIB: a global model of terrestrial biological productivity. Global Biogeochem. Cycles, 8, 255-270, 1994.
(2) MODEL TYPE (E.G. ECOSYSTEM, BIOGEOGRAPHY, DGVM):
Ecosystem model with an optional biogeographic module.
Plant functional types (PFTs):
a) C3/C4 grasslands
b) C3/C4 crops
c) needleleaves (deciduous and evergreen)
d) broadleaves (deciduous and evergreen)
(3) PRIMARY MODEL PURPOSE:
Calculate the influence of the seasonal and interannual climate changes on the carbon fluxes between continental biosphere and atmosphere.
(4) MODELING APPROACH:
Photosynthetic assimilation: mechanistic models of Farquhar (C3) and Collatz (C4).
Reservoir models for carbon in 2 biomass pools (leaves and wood), 2 litter pools (leaves and wood) and 1 soil carbon pool.
(5) RESOLUTION (SPATIAL, TEMPORAL)
Standard spatial resolution: grid cells of 1° x 1° in longitude and latitude (all PFTs are included in every grid cell according various fractional distributions). Please, see comment 1.
Photosynthetic assimilation calculated every 2 hours.
Climatic fields (temperature, precipitation) calculated every day by stochastic weather generator using monthly climatic fields.
Carbon fluxes and contents calculated every day for every reservoir of every PFT.
(6) SPATIAL AND TEMPORAL SCALE(S) AT WHICH THE MODEL RESULTS SHOULD BE CONSIDERED:
1° x 1°. Please see comment 1.
Monthly averages of the results during a year. Daily results could be compared if daily measurements are available. Please see comment 2.
(7) PROCESSES AND PROCESS COMPONENTS SIMULATED (E.G. CARBONG: GPP, NPP, NEP):
Carbon:
a) fapar (fraction of absorbed photosynthetically active radiation)
b) LAI (Leaf Area Index)
c) GPP
d) Ra (Growth and maintenance autotrophic respirations)
e) NPP = GPP - Ra
f) Rh (Heterotrophic respiration)
g) NEP = NPP - Rh
Water:
a) Soils (simple bucket, saturated/unsaturated flow, controls on water movement through the profile, etc.):
b) Improved bucket model (IBM) is a one-layer model with calculation of hydraulic conductivity to estimate deep drainage. It provides evapotranspiration fluxes and interception by foliage.
c) Energy balance: (e.g. latent, sensible heat, aet, pet):
PET from Penman
AET
d) Snow: calculated in IBM
e)'Order' of water balance: (e.g. incoming water is first evaporated from plant/soil surface, then infiltration, transpiration, runoff)
Interception is parameterized
Nitrogen: not yet included
(8) SIMULATED RESERVOIRS
Carbon:
For each PFT:
vegetation: 2 pools (leaves and woody material)
litter: 2 pools (leaves and woody material)
SOC: 1 pool
Nitrogen: none
vegetation:
litter:
SON:
Soil water: 1 snow pool and 1 water pool
(9) CALIBRATION VARIABLE(S) AND METHOD:
The ratio between root and microbial contributions to soil respiration has been determined for grasslands and forests in such a way to optimize the agreement between observation and simulation of seasonal changes in atmospheric CO2. Atmospheric transport of CO2 has been simulated with model TM2 driven by carbon fluxes (NEP) from CARAIB.
(10) SCALING OF THE PROCESSES TO THE GRID CELL:
Leaf level: photosynthesis and stomatal exchange
Plant and ecosystem level: canopy model, plant and soil processes
Regional level (1° x 1°): area weighted average of several PFTs in each grid cell
(11) DISTURBANCE: (FIRE, GRAZING, HARVEST, TREE REMOVAL, ETC.)
None
(12) VEGETATION I/O: (E.G. POTENTIAL, ACTUAL)
Standard simulations: actual vegetation is considered, and crops are C3 or C4 plants.
Optionally, the model predicts potential vegetation if biogeography module is used.
(13) INPUT DRIVERS (CLIMATE, SITE, VEG, SOILS) AND RESOLUTION (E.G. DAILY, MONTHLY) REQUIRED FOR MODEL INITIALIZATION:
In standard version, CARAIB needs monthly climatic fields with the resolution 1° x 1° in longitude and latitude. These fields are (monthly values)
a) surface air temperature
b) range of daily temperature variation (Tmax — Tmin)
c) precipitation
d) fractional cloud cover or sunshine hours
e) magnitude of surface wind
f) relative humidity
Please, see also comment 2.
The model also needs soil texture (fractions of sand, silt and clay) and rooting depth.
(14) ADDITIONAL COMMENTS:
comment 1: the standard resolution of the model is 1° x 1° but it can run at 0.5° x 0.5°, provided that all inputs are supplied at the same resolution.
comment 2: it should be interesting to dispose on daily fields of temperature and precipitation, at least in some regions during some parts of the year, for example during growing period.