References of "Warnant, Pierre"
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See detailBiospheric carbon stocks reconstructed at the Last Glacial Maximum: comparison between general circulation models using prescribed and computed sea surface temperatures
Otto, D.; Rasse, Daniel; Kaplan, J. et al

in Global and Planetary Change (2002), 33(1-2), 117-138

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution ... [more ▼]

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution of the vegetation inferred from physiological processes and climatic constraints. In this fourth version of CARAIB, we differentiate ground-level grasses from tree canopies, which allows us to determine the light available to grasses as a direct function of the leaf area index (LAI) of the forest canopy. Both of these storeys are potentially composed of several plant functional types (PFT). The cover fraction of each PFT within each storey is estimated according to its respective net primary productivity (NPP). A biome is assigned to each grid cell on the basis of three physiological criteria: (1) the cover fraction, (2) the NPP, and (3) the LAI; and two climatic constraints: (1) the growing degree-days (GDD) and (2) the lowest temperature reached during the cold season (T-min), which are well-known indices of vegetation expansion boundaries. Total biospheric carbon stocks (vegetation + soil) are reconstructed by forcing the model with eight climatic scenarios of the Last Glacial Maximum (LGM, 21 ka BP), which were obtained from the Palco-Modelling Intercomparison Project (PMIP) from four general circulation models (MRI2, UGAMP, LMD4, and GEN2) using prescribed and computed sea surface temperatures (SSTs). The model was also forced with a current climate together with a preindustrial atmospheric CO2 level of 280 ppm as reference simulation, To validate the model, current biome distribution is reconstructed and compared, for the modem climate, with two distributions of potential vegetation and, for the LGM, with pollen data. The model simulations are in good agreement with broad-scale patterns of vegetation distribution, The results indicate an increase in the total biospheric carbon stock of 827.8-1106.1 Gt C since the LGM. Sensitivity analyses were performed to discriminate the relative effects of the atmospheric CO, level ("fertilization effect"), the climate (present or LGM), and the sea level. Our results suggest that the CO, fertilization effect is mostly responsible for the total increase in vegetation and soil carbon stocks. The four GCMs diverged in their predicted responses of continental climate to calculated SSTs. Only one of them, i.e., MRI2, predicted a marked decline of the continental temperatures in response to lower calculated SSTs. For this GCM, the effect of reduced SSTs on continental biospheric carbon stocks was a decrease of 544.1 Gt for the soil carbon stock and of 283.7. [less ▲]

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See detailImpact of crops on biomass and soil carbon: steady state simulations
Nemry, B.; François, Louis ULg; Gérard, Jean-Claude ULg et al

in Cramer, W.; Doherty, R.; Hulme, M. (Eds.) et al Climate Scenarios for Agricultural, Forest and Ecosystem Impacts (2000)

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See detailComparison of vegetation distributions and terrestrial carbon budgets reconstructed for the last glacial maximum with several biosphere models
François, Louis ULg; Kaplan, J.; Otto, D. et al

in Braconnot, P. (Ed.) PMIP, 2000: Paleoclimate Modelling Intercomparison Project (PMIP), Proceedings of the Third PMIP workshop (2000)

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See detailThe interannual change of atmospheric CO2: contribution of subtropical ecosystems?
Gérard, Jean-Claude ULg; Nemry, B.; François, Louis ULg et al

in Geophysical Research Letters (1999), 26(2), 243-246

The global terrestrial carbon cycle model CARAIB (CARbon Assimilation In the Biosphere) is used to study the response of the terrestrial ecosystems to the large scale climate variations over the period ... [more ▼]

The global terrestrial carbon cycle model CARAIB (CARbon Assimilation In the Biosphere) is used to study the response of the terrestrial ecosystems to the large scale climate variations over the period 1980-1993. The global net carbon exchange flux with the atmosphere is calculated and compared with the terrestrial contribution derived from the deconvolution of the atmospheric CO2 and delta(13)C measurements. A fairly large CO2 biospheric source is predicted during the strong El Nino events of 1982-83 and 1986-87 as a consequence of the induced global warming. The direct and indirect temperature controls of the primacy production and respiration dominate the CO2 anomaly. An analysis of the relative contribution by latitudinal bands and ecosystems shows that low-latitude vegetation dominates the variability at the El Nino time scale. In savannas, the model indicates that the interannual changes result, to a large extent, from the control of soil water content on gross primary production (GPP). In the tropical cain forests, both respiration and GPP contribute to the response of the net biospheric flux. [less ▲]

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See detailCarbon stocks and isotopic budgets of the terrestrial biosphere at mid-Holocene and last glacial maximum times
François, Louis ULg; Godderis, Y.; Warnant, Pierre ULg et al

in Chemical Geology (1999), 159(1-4), 163-189

The carbon fluxes, stocks and isotopic budgets of the land biosphere at mid-Holocene (6 ka BP) and last glacial maximum (21 ka BP) times are reconstructed with the CARbon Assimilation In the Biosphere ... [more ▼]

The carbon fluxes, stocks and isotopic budgets of the land biosphere at mid-Holocene (6 ka BP) and last glacial maximum (21 ka BP) times are reconstructed with the CARbon Assimilation In the Biosphere (CARATB) model forced with two different sets of climates simulated by the European Centre-HAMburg (ECHAM) and LMD general circulation models. It is found that the trends predicted on the basis of both sets of GCM climatic fields are generally consistent with each other, although substantial discrepancies in the magnitude of the changes may be observed. Actually, these discrepancies in the biospheric results associated with the use of different GCM climatic fields are usually smaller than the differences between biospheric runs performed while considering or neglecting the CO2 fertilization effect (which might, however, be overestimated by the model due to uncertainties concerning changes in nutrient availability). The calculated changes with respect to the present of the biosphere carbon stock range from - 132 to + 92 Gt C for the mid-Holocene and from -710 to +70 Gt C for the last glacial maximum. It is also shown that the relative contribution of the material synthesized by C-4 plants to the total biomass of vegetation, litter and soils was substantially larger at mid-Holocene and last glacial maximum times than today. This change in the relative importance of the C-3 and C-4 photosynthetic pathways induced changes in the C-13 fractionation of the land biosphere. These changes in the average biospheric fractionation resulting from the redistribution of C-3 and C-4 plants were partly compensated for by changes of opposite sign in the fractionation of C-3 plants due to the modification of the intercellular CO2 pressure within their leaves. With respect to present times, the combination of both processes reduced the C-13 discrimination (i.e., less negative fractionation) of the land biosphere by 0.03 to 0.32 parts per thousand during the mid-Holocene and by 0.30 to 1.86 parts per thousand at the last glacial maximum. (C) 1999 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailStochastic generation of meteorological variables and effects on global models of water and carbon cycles in vegetation and soils
Hubert, Benoît ULg; François, Louis ULg; Warnant, Pierre ULg et al

in Journal of Hydrology (1998), 213(1-4), 318-334

Global models of water and carbon cycles in continental vegetation and soils are usually forced with monthly mean climatic data-sets and thus neglect day to day variations of the weather. This treatment ... [more ▼]

Global models of water and carbon cycles in continental vegetation and soils are usually forced with monthly mean climatic data-sets and thus neglect day to day variations of the weather. This treatment may be justified for empirical models based on parametrizations validated at a monthly timescale. Mechanistic models handling hydrological and biological processes at much shorter timescales might, however, be largely affected by such an approximation, since the various processes described are highly nonlinear. A random generator of daily precipitations and temperatures applicable at the global scale has thus been developed from worldwide meteorological data covering 6 years of observations. The probability of a wet day is correlated to the weather encountered the previous day. The amount of precipitation, the daily mean temperature and the diurnal. range of temperature are described from the statistical point of view by the cumulative distribution functions (CDF) of three random variables. The CDF's a relative to temperatures are different for rainy and dry days. This stochastically generated weather field is used as input to IBM (Improved Bucket Model) and CARAIB (CARbon Assimilation In the Biosphere), two global models of respectively soil hydrology and vegetation productivity. Large differences in both the geographical distribution and the global value of soil water, vegetation productivity and carbon stocks are obtained between the model runs using monthly uniform weather on one side and randomly generated weather on the other. The main contribution to this difference at the global scale arises from the precipitation generation occurring as a result of high degree of nonlinearity of the interception scheme used in IBM. (C) 1998 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailModelling the glacial-interglacial changes in the continental biosphere
François, Louis ULg; Delire, Christine; Warnant, Pierre ULg et al

in Global and Planetary Change (1998), 17

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to ... [more ▼]

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to drive the biosphere model are derived from results of the ECHAM2 General Circulation Model (GCM). Six model simulations (four under typical interglacial and two under typical glacial climatic conditions) were performed to analyse the roles of different environmental changes influencing the biospheric net primary productivity (NPP) and carbon stocks. The main differences between these simulations come from the adopted CO, levels in the atmosphere, the presence or absence of crops and from changing continental boundaries. The variation of the terrestrial carbon stocks since the LGM are estimated by comparing the pre-agricultural (280 ppm of CO2, no crops, modern climate) and the full glacial simulations (200 ppm of CO2, LGM climate reconstruction). Our model predicts a global NPP increase from 38 Gt C year(-1) to 53 Gt C year(-1) during the deglaciation, a substantial part of that change being due to CO, fertilization. At the same time, the terrestrial biosphere would have fixed between 134 (neglecting CO2 fertilization effects) and 606 Gt C. The treatment of both the C-3 and C-4 photosynthetic pathways in the CARAIB model enabled us further to reconstruct the partitioning between C, and C, plants. Following our experiments, 29.7% of the total biospheric carbon stock at the LGM was C-4 material, compared to an interglacial fraction of only 19.8%. The average biospheric fractionation factor was similar to 1.5 parts per thousand less negative at LGM than it is today. Considering an atmospheric delta(13)C 0.5 +/- 0.2 parts per thousand lower at LGM than at pre-industrial times, the 606 Gt C transfer would lead to a global ocean delta(13)C shift of roughly -0.41 parts per thousand, fully consistent with currently available data. For the smaller change of 134 Gt C obtained without the CO2 fertilization effect, this shift would only be on the order of -0.10 parts per thousand. (C) 1998 Elsevier Science B,V. All rights reserved. [less ▲]

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See detailA global model of the biosphere : validation and applications to present and past climatic conditions
François, Louis ULg; Gérard, Jean-Claude ULg; Nemry, Bernard et al

in Sciences Géologiques. Bulletin (1997), 50(1-4), 89-107

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See detailThe seasonality of the CO2 exchange between the atmosphere and the land biosphere: A study with a global mechanistic vegetation model
Nemry, B.; François, Louis ULg; Warnant, Pierre ULg et al

in Journal of Geophysical Research (1996), 101(D3), 7111-7125

Two simulations of the seasonal variation of the global atmospheric CO2 distribution are obtained by combining an atmospheric transport model, two parameterizations of soil heterotrophic respiration (SHR ... [more ▼]

Two simulations of the seasonal variation of the global atmospheric CO2 distribution are obtained by combining an atmospheric transport model, two parameterizations of soil heterotrophic respiration (SHR), and a mechanistic model of carbon assimilation in the biosphere (CARAIB) that estimates the net primary production (NPP) of continental vegetation. The steady state hypothesis of the biosphere allows the spatial distribution and the global content of the soil carbon to be expressed as a function of the root fractions of soil respiration under forested and herbaceous vegetation covers. The sensitivity of the modeled CO2 signal to the wind field does not exceed the observed interannual variability. The influence of the various vegetation zones is quantified by the Fourier analysis of the modeled atmospheric signal. In the northern hemisphere, the temperate ecosystems dominate the seasonal atmospheric signal of the extratropical latitudes. The ecosystems of the tropical northern zone determine the local signal, while the southern tropical ecosystems influence largely the signal in the whole southern hemisphere. The results give credence to the mechanistic modeling of NPP since the simulated atmospheric signal is comparable with that obtained with normalized difference vegetation index (NDVI) based diagnostic models coupled with a parameterization of SHR fitted to optimize the atmospheric signal. [less ▲]

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See detailSeasonal and interannual influences of the terrestrial ecosystems on atmospheric CO2: a model study
François, Louis ULg; Nemry, Bernard; Warnant, Pierre ULg et al

in Physics & Chemistry of the Earth - Parts A/B/C (1996), 21

The prognostic CARAIB (Carbon Assimilation In the Biosphere) model has been used in conjunction with the Max-Planck Institut TM2 atmospheric transport model to calculate the atmospheric CO2 fluctuations ... [more ▼]

The prognostic CARAIB (Carbon Assimilation In the Biosphere) model has been used in conjunction with the Max-Planck Institut TM2 atmospheric transport model to calculate the atmospheric CO2 fluctuations at the global scale. Two applications are briefly described. In the first one, the seasonal CO2 variation is calculated and a Fourier analysis is performed to determine the relative contributions of the various vegetation types. It is found that the seasonal signal is dominated by the grasslands and needle leaf forests in the northern boreal and temperate zones. In the southern hemisphere, tropical deciduous forests and grasslands make the primary contribution. In the second application, the net primary productivity (NPP), soil heterotrophic respiration (SHR) and net ecosystem productivity (NEP) are calculated for years 1987 and 1988 with the model driven by observed climatic variables. Preliminary results indicate that the NEP variations between these two years are strongly dominated by tropical ecosystems. However, it is shown that the results are strongly dependent on the dataset used for the 1987-88 temperature record, raising the question of reliability of sudl modelling studies of the interannual variability of the biosphere. 01997 Elsevier Science Ltd [less ▲]

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See detailA new vegetation map and its inclusion in a global biosphere model
Warnant, Pierre ULg; François, Louis ULg; Nemry, Bernard et al

in Guyot (Ed.) Photosynthesis and remote sensing (1995)

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See detailStochastic generation of precipitation and effect on vegetation net primary production
Hubert, Benoît ULg; François, Louis ULg; Warnant, Pierre ULg

in Global Energy and Water Cycle Experiment news (1995), 5

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See detailCarbon cycle modelling and remote sensing
François, Louis ULg; Gérard, Jean-Claude ULg; Warnant, Pierre ULg

in Space scientific research in Belgium, Vol. III, Earth Observation, Part 2 (1994)

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See detailCARAIB - A global model of terrestrial biological productivity
Warnant, Pierre ULg; François, Louis ULg; Strivay, David ULg et al

in Global Biogeochemical Cycles (1994), 8(3), 255-270

CARAIB, a mechanistic model of carbon assimilation in the biosphere estimates the net primary productivity (NPP) of the continental vegetation on a grid of 1 degrees x 1 degrees in latitude and longitude ... [more ▼]

CARAIB, a mechanistic model of carbon assimilation in the biosphere estimates the net primary productivity (NPP) of the continental vegetation on a grid of 1 degrees x 1 degrees in latitude and longitude. The model considers the annual and diurnal cycles. It is based on the coupling of the three following submodels; a leaf assimilation model including estimates of stomatal conductance and leaf respiration, a canopy model describing principally the radiative transfer through the foliage, and a wood respiration model. Present-day climate and vegetation characteristics allow the discrimination between ecotypes. In particular, specific information on vegetation distribution and properties is successfully used at four levels; the leaf physiological level, the plant level, the ecosystem level, and the global level. The productivity determined by the CARAIB model is compared with local measurements and empirical estimates showing a good agreement with a global value of 65 Gt C yr(-1). The sensitivity of the model to the diurnal cycle and to the abundance of C-4 species is also tested. The productivity slightly decreases (10%) when the diurnal cycle of the temperature is neglected. By contrast, neglecting the diurnal cycle of solar irradiance produces unrealistically high values of NPP. Even if the importance of this increase would presumably be reduced by the coupling of CARAIB with a nutrient cycle model, this test emphasizes the key role of the diurnal cycle in a mechanistic model of the NPP. Uncertainties on the abundance and spatial distribution of C-4 plants may cause errors in the NPP estimates, however, as demonstrated by two sensitivity tests, these errors are certainly lower than 10% at the global scale as shown by two tests. [less ▲]

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See detailForcing of a global model of plant productivity with climatic and remote sensing data
Warnant, Pierre ULg; François, Louis ULg; Strivay, David ULg et al

in Veroustraete, F.; Ceulemans, R. (Eds.) Vegetation, modelling and climatic change effects (1994)

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See detailCoupled modelling of the global chemical-climatic changes due to human activities
Gérard, Jean-Claude ULg; François, Louis ULg; Delire, C. et al

in Proceedings of the global change symposium (1993)

Detailed reference viewed: 23 (9 ULg)