Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 2 2007 10.5194/acpd-7-4761-2007 http://www.atmos-chem-phys-discuss.net/7/4761/2007/ http://www.atmos-chem-phys-discuss.net/7/4761/2007/acpd-7-4761-2007.html http://www.atmos-chem-phys-discuss.net/7/4761/2007/acpd-7-4761-2007.pdf 4761 4779 2007-04-05 Past and future scenarios of the effect of carbon dioxide on plant growth and transpiration for three vegetation types of southwestern France J.-C. Calvet calvet@meteo.fr A.-L. Gibelin J.-L. Roujean E. Martin P. Le Moigne H. Douville J. Noilhan CNRM/GAME (Météo-France, CNRS), Toulouse, France The sensitivity of an operational CO₂-responsive land surface model (the ISBA-A-gs model of Météo-France) to the atmospheric CO₂ concentration, [CO₂], is investigated for 3 vegetation types (winter wheat, irrigated corn, coniferous forest). Past (1960) and future (2050) scenarios of [CO₂] corresponding to 320 ppm and 550 ppm, respectively, are explored. The sensitivity study is performed for 4 annual cycles presenting contrasting conditions of precipitation regime and air temperature, based on continuous measurements performed on the SMOSREX site near Toulouse, in southwestern France. A significant CO₂-driven reduction of canopy conductance is simulated for the irrigated corn and the coniferous forest. The reduction is particularly large for corn, from 2000 to 2050 (–18%), and triggers a drop in optimum irrigation (–30 mm y^−1). In the case of wheat, the response is more complex, with an equal occurrence of enhanced or reduced canopy conductance. Calvet, J.-C., Noilhan, J., Roujean, J.-L., Bessemoulin, P., Cabelguenne, M., Olioso, A., and Wigneron, J.-P.: An interactive vegetation SVAT model tested against data from six contrasting sites, Agric. For. Meteorol., 92, 73–95, 1998. Calvet, J.-C. and Soussana, J.-F.: Modelling CO₂-enrichment effects using an interactive vegetation SVAT scheme, Agric. For. Meteorol., 108(2), 129–152, 2001. 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