Canicules et sécheresses en Méditerranée : contributions des processus couplés surface-atmosphère à méso-échelle

Abstract : In a context defined as that of global warming, with fears that one summer out of two could be very similar to the 2003 European heat wave, the significant role played by droughts and land-atmosphere coupling in the enhanced and persistent high temperatures during heat-wave events has been highlighted by various studies. I have developed an original classification based on the spatial structures of the heat waves ocurring in the Euro-Mediterranean area. Classification are generally designed to classify numerous events, so we have had to adapt to classifying rare events, by introducing three criteria grounded on temperature and the spatio-temporal extension of the phenomena to be described. The classification has enabled us to sort out six different categories of heat wave. In course of the investigation, I then proceeded to focus on one of the categories, id est on Westen Europe heat wave. I carried out numerical sensitivity tests in order to analyse how the hydric deficit of soils contributes to amplifying heat waves and was able to bring out different behaviours. In the continental plains, the atmospheric boundary layer temperatures are largely controlled by local dry convection processes. In the mountainous and coastal areas, mesoscale circulations such as slope winds and sea breezes contribute to mitigating heat waves by allowing fresh and moist air to advect and precipitations to form. The effect of vegetation on heat waves was also examined. To do so, I have developed modelling tools which couple atmospheric dynamics with vegetative dynamics and thus present an innovative view on heatwave and drought conditioning processes in Western Europe. This modelling development is part of a larger project that aims at developing a model for regional climatic system and which has been undertaken at the Institut Pierre Simon Laplace (IPSL) as part of the MORCE-MED project. This question has so far been little addressed in the scientific literature. I have shown that the inclusion of an interactive vegetation into modelling enable to simulate the modifications of the phenological cycle that control plant growth and development as well as evapotranspiration. Used to analyse the heat waves of June and August 2003, I have been able to demonstrate that the interaction of vegetation had a mitigating effect on the June 2003 heat wave, while it had a reversed effect in August, id est that of reinforcing. Lastly, we have measured the effects of land cover change that would allow to mitigate the consequences of heat waves on humans. In a preliminary study, I replaced anthropized surfaces (mainly agricultural land) by forests and meadows. There again, the effects noted were more contrasted than expected and presented a mitigation of the heat in June and an increase in the temperatures in August, with a high spatial variability on a mesoscale.
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Submitted on : Tuesday, October 30, 2012 - 3:09:34 PM
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Marc Stéfanon. Canicules et sécheresses en Méditerranée : contributions des processus couplés surface-atmosphère à méso-échelle. Géophysique [physics.geo-ph]. Ecole Polytechnique X, 2012. Français. ⟨pastel-00747124⟩

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