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Biosphere-atmosphere interactions coupled with carbon dioxide and soil moisture changes

Niyogi, Devdutta Sadananda

Titre : Biosphere-atmosphere interactions coupled with carbon dioxide and soil moisture changes

Auteur : Niyogi, Devdutta Sadananda

Université de soutenance : NORTH CAROLINA STATE UNIVERSITY

Grade : Doctor of Philosophy (PhD) 2001

Objectives of this research are to analyze coupled biosphere-atmosphere interactions with changes in soil moisture, CO2 availability and related environmental conditions. For this, a CO2 based Gas exchange Evapotranspiration Model (called GEM), with explicit photosynthesis based vegetation and soil moisture effects was developed. GEM was coupled to a prognostic hydrometeorological scheme, and a detailed PBL/atmospheric model. The coupled biosphere model (GEM) was validated through 11 different case studies with contrasting micrometeorological field conditions. A statistical-dynamical study was performed using observations from a semi-arid tropical (HAPEX-Sahel), and a mid-latitudinal (FIFE) field experiment and simulated results from a land surface model : `Simple SiB’. For the two cases, direct effects are similar, while higher order interactions are different. Also, for the water-stressed semi and tropical case, there was relatively very little interaction between the vegetation and the soil variables, suggesting instead of the `effective surface’ flux representation, the water-stressed and tropical region will require explicit soil and vegetation flux estimation. The effect of adopting photosynthesis-based vegetation schemes such as GEM in place of the traditional Jarvis- scheme in land surface models was also addressed. It appears uncertainties would be reduced with the use of the photosynthesis scheme as compared to the diagnostic Jarvis-type approach. Additionally, it is shown that deposition velocities could be efficiently estimated for different gases (such as ozone, and nitrogen compounds) using a photosynthesis- based vegetation scheme. Another hypothesis tested the role of direct and interactive exchanges of the CO2 and soil moisture changes on transpiration, stomatal resistance, photosynthesis, and air temperature for different global biomes. Finally, a concept of differential vegetation characteristics (DVC) based subgrid scale (SGS) heterogeneity was proposed, taking as an example coexisting C3 grasses and shrubs and C4 grass over a natural landscape. The errors were largest for biophysical variables such as photosynthesis, and CO2 scenarios. To address the issue of developing grid-averaged values under DVC-SGS, empirical relations were proposed for photosynthesis-based effects in the biosphere-atmosphere interactions for varying environmental conditions.


Page publiée le 11 novembre 2013, mise à jour le 21 octobre 2019