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PhD Defense


Title : Modelisation of carbon, energy and water fluxes between the atmosphere and sahelien ecosystems with a global vegetation model.

Date and time : The 29-05-2012 at 10h30

Type : thèse

Université qui délivre le diplôme : AgroParisTech-ENGREF

Location : LSCE, Orme des Merisiers. Salle 17C (bâtiment 701)
Members of jury :

Eric Mougin, Laboratoire Géosciences Environnement Toulouse (rapporteur)

Thierry Lebel, Laboratoire d'étude des Transferts en Hydrologie et Environnement. Saint Martin d’Hères (rapporteur)

Jan Polcher, Institut Catalan des sCiences du Climat, Barcelone(examinateur)

Cyril Kao, AgroParisTech-ENGREF, Paris (examinateur)

Pierre Hiernaux, laboratoire Géosciences Environnement Toulouse (examinateur)

Jérôme Demarty, laboratoire HydroSciences Montpellier (examinateur)

Catherine Ottlé, LSCE/IPSL, Gif sur Yvette (directrice de thèse)

Philippe Ciais, LSCE/IPSL, Gif sur Yvette (directeur de thèse)

Summary :

This thesis is an attempt to improve the representation of sahelian rangelands and fallows in the vegetation model ORCHIDEE. It has largely been constructed on the use of data acquired within the AMMA program on the sahelian sites of Agoufou and Wankama (which has been conducted in collaboration with colleagues from the Géosciences Environnement Toulouse and HydroSciences Montpellier labs).

This work has been conducted with a version of the model that used the vertically discretized soil hydrology scheme developed by de Rosnay et Polcher [2002] and d'Orgeval et al. [2008]. The use of this code in conjonction with the module that brings a prognostic representation of the phenology, STOMATE has been the subject of much work.

At the same time, different modifications of the phenology that could be relevant for water-limited ecosystems at large have been implemented. At a broader scale, the model has then been applied over West Africa, in order to characterize its ability to describe the phenology of the main ecosystems between the Sahara and the Gulf of Guinea, when forced with the climatic datasets that are available.

In particular, the interest and limits of the developments that have been achieved in this thesis are presented. Finally, the evolution of the vegetation cover simulated by the model is compared to the one observed by remote sensing between 1982 and 2009

This modelisation work has been achieved in parallel with a large bibliography study on the regreening of the Sahel, that is presented as an introductory chapter to the thesis. A methodological work on the characterization of the systematic errors of the ORCHIDEE surface model has also been conducted (Wang et al., submitted)

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