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AbstractAbstract
[en] Peatlands are widely present in northern latitudes and especially in permafrost regions. They contain a high carbon stock and are one of the greatest natural sources of methane. Their representation in a climate model is crucial to improve the one of the carbon cycle. Moreover, the contribution of methane peatland emissions remains uncertain. Methane emissions from peatlands strongly depend on the climate and are influenced primarily by temperature and soil moisture. Meanwhile, climate change is particularly severe at these latitudes and leads to thawing permafrost with increasing the active layer depth. This large carbon reservoir may be partially mobilized and emitted as CO2 or CH4, depending on hydrological conditions at the surface. The aim of this PhD thesis is to represent northern peatlands in the ORCHIDEE land surface model. This development is carried out in the version of the model that incorporates processes in high latitudes such as the soil freezing. Peatlands are represented by a specific hydrological scheme which improves the exchange of energy and water. The difficulty is based on the representation of local peatlands processes across a global climate model. Some biological properties were also considered to represent better vegetation of these environments. To do so, peatlands are integrated as a new type of vegetation and represented by a fraction of a grid, based on observations. The hydrological behaviour and the impact of this integration are estimated at the boreal scale as well as regionally. This development then allows estimate changes in the hydrology of peatlands due to global warming. Studying the changes in hydrology of peatlands by the end of the 21. century will improve the prediction of future changes in their CH4 emissions. This development work was then applied to determine the evolution of methane emissions. Peatlands are one of the largest natural sources of methane and control more than 70% inter-annual variability of atmospheric concentration of CH4. Methane emissions result from various physical and biological processes such as methano-genesis and the methano-trophy. To represent these processes, a flux density model, integrated in ORCHIDEE, was adapted for peatlands to estimate their methane emissions. The evolution of these emissions is studied between the early 20. and late 21. centuries under different climate scenarios. (author)
[fr]
Les tourbieres sont largement presentes dans les hautes latitudes nord et plus particulierement dans les regions de pergelisols. Elles contiennent un important stock de carbone et constituent l'une des plus grandes sources naturelles de methane. Leur representation dans un modele de climat est alors primordiale pour ameliorer celle du cycle du carbone. De plus, la contribution des emissions de methane des tourbieres reste encore incertaine et de nombreuses incertitudes persistent. Les emissions de methane des tourbieres dependent fortement du climat et sont influencees principalement par la temperature et l'humidite du sol. Parallelement, le rechauffement climatique particulierement prononce a ces latitudes conduit au degel des pergelisols avec une augmentation de la profondeur de la couche active. Ce grand reservoir de carbone peut etre partiellement mobilise et emis sous forme de CO2 ou CH4, en fonction des conditions hydrologiques a la surface. L'objectif de ces travaux de these consiste a representer les tourbieres des hautes latitudes dans le modele de surface ORCHIDEE. Ce developpement est effectue dans la version du modele qui integre les processus des hautes latitudes tels que le gel des sols. Les tourbieres sont representees par un schema hydrologique specifique ce qui ameliore les echanges en energie et en eau. La difficulte repose sur la representation des processus locaux des tourbieres a l'echelle d'un modele de climat global. Certaines proprietes biologiques ont egalement ete prises en compte afin de mieux representer la vegetation de ces milieux. Pour cela, les tourbieres sont integrees comme un nouveau type de vegetation et representees par une fraction de grille, basee sur des observations. Le comportement hydrologique et l'impact de cette integration sont evalues a echelle des hautes latitudes ainsi qu'a echelle regionale. Ce developpement permet d'estimer ensuite l'evolution de l'hydrologie des tourbieres suite au rechauffement climatique. Les changements de l'hydrologie des tourbieres d'ici la fin du siecle permettent de mieux evaluer les variations futures de leurs emissions de CH4. Ce travail de developpement a ensuite ete applique pour determiner l'evolution des emissions de methane. Les tourbieres constituent l'une des plus grandes sources naturelles de methane et controlent a plus de 70 % la variabilite interannuelle de la concentration atmospherique de CH4. Les emissions de methane resultent de differents processus physiques et biologiques tels que la methanogenese et la methanotrophie. Pour representer ces processus, un modele de densite de flux existant, integre dans ORCHIDEE, a ete adapte pour les tourbieres afin d'estimer les emissions de methane des tourbieres des hautes latitudes. L'evolution de ces emissions est etudiee entre le debut du 20eme et la fin du 21eme siecles selon differents scenarios climatiques. (auteur)Original Title
Representation des tourbieres des hautes latitudes nord dans un modele de surface: developpement d'un schema hydrologique et estimations des emissions de methane
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20 Jun 2016; 216 p; 135 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Sciences de la Terre, de l'Univers et de l'Environnement
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Report
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Thesis/Dissertation
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