Carbon cycle data assimilation on Bethy high resolution
Vegetation water status forms a crucial link between the global carbon and water cycles due to its control on both photosynthesis and transpiration, through the common pathway of the two fluxes, the leaf stomata. Since CO2 levels in the atmosphere have been rising substantially, this tight link has profound impacts on both the carbon uptake and the evapotranspiration rates of plants. At present there is still a lack of reliable data on terrestrial biosphere carbon fluxes at the global scale and model predictions still vary quite widely. Current models determine the degree of plant water stress, and thus the control on water and carbon fluxes, by the amount of plant-available water in the soil and the atmospheric demand for water only. The vegetation water reservoir itself is not taken into account. The relative influence of vegetation water status on global carbon and water fluxes has thus never been studied before. Passive microwave remote sensing has the unique ability to provide gravimetric values of vegetation water content, through measurements of the vegetation optical depth. The proposed project will combine passive microwave measurements of vegetation optical depth from the SMOS mission with EVI data from MODIS, in order to obtain a gravimetric vegetation water content product. The terrestrial biosphere model BETHY, which forms the core of the Carbon Cycle Data Assimilation System (CCDAS), will be modified in order to include a vegetation water reservoir. The satellite-derived vegetation water content will subsequently be used in the CCDAS as a constraint on the parameters in the formulation of the processes regulating the terrestrial carbon cycle. The results will help to improve estimations of terrestrial carbon and water fluxes, and increase our understanding of the role of vegetation water in these. This work concerns a completely novel application of a passive microwave-based vegetation product, and it will be the first time that the vegetation water reservoir is taken into account in terrestrial biosphere modelling. The proposed project would be a continuation of ESA’s currently-running VEGWAC project. The project will be carried out by a postdoctoral researcher, under supervision of a senior researcher. The team has a strong network of collaborative partners in place, and extensive experience in the relevant fields of research.