Publication issue des travaux du projet MORCE MED.

Anav et coll. ont étudié les effets potentiels de l'ozone sur la photosynthèse et l'indice de surface foliaire et, inversement, les impacts de la végétation sur la concentration atmosphérique en ozone, dans la région euro-méditerranéenne. Ils ont mené ces travaux à l'aide du modèle de biosphère continentale ORCHIDEE à haute résolution (30 km) couplé au modèle de chimie atmosphérique CHIMERE, sur l'année 2002.
Le modèle estime que, durant cette année, l'ozone troposphérique a provoqué une réduction annuelle d'environ 22% de la production primaire nette et une diminution d'environ 15% de l'indice de surface foliaire. Les impacts les plus forts ont eu lieu en été, lorsque les concentrations en ozone troposphérique étaient les plus élevées.

Résumé en anglais

Impact of tropospheric ozone on the euro-mediterranean vegetation

The impact of ozone (O₃) on European vegetation is largely under-investigated, despite huge areas of Europe are exposed to high O₃ levels and which are expected to increase in the next future. We studied the potential effects of O₃ on photosynthesis and leaf area index (LAI) as well as the feedback between vegetation and atmospheric chemistry using a land surface model (ORCHIDEE) at high spatial resolution (30 km) coupled with a chemistry transport model (CHIMERE) for the whole year 2002. Our results show that the effect of tropospheric O₃ on vegetation leads to a reduction in yearly gross primary production (GPP) of about 22% and a reduction in LAI of 15–20%. Larger impacts have been found during summer, when O₃ reaches higher concentrations. During these months the maximum GPP decrease is up to 4 g C m⁻² day⁻¹, and the maximum LAI reduction is up to 0.7 m² m⁻². Since CHIMERE uses the LAI computed by ORCHIDEE to estimate the biogenic emissions, a LAI reduction may have severe implications on the simulated atmospheric chemistry. We found a large change in O₃ precursors that however leads to small changes in tropospheric O₃ concentration, while larger changes have been found for surface NO₂ concentrations.