Integrating SPOT-VEGETATION 10-yr Time Series and Land Surface Modelling to Forecast the Terrestrial Carbon Dynamics in a Changing Climate

Moreau, Inès [UCL] Defourny, Pierre [UCL] Hanert, Emmanuel [UCL] De Weirdt, Marjolein [UGent] Verbeeck, Hans [UGent]

(eng) In tropical regions, the seasonal and interannual variability of carbon fluxes is still uncertain, and a weak or even no seasonality is taken into account in global vegetation models. However, phenology patterns in tropical rainforests can significantly influence global dynamics of carbon and water fluxes and climate. Previous studies of moist tropical forests based on field and satellite data showed an increase in the gross primary production (GPP) or vegetation index during the dry season. In this study, we explore the seasonal characterization of leaf phenology in the Amazon basin through vegetation indices, using a long time series of SPOT-VEGETATION data (2000 – 2009) at a spatial resolution of 1 km, in order to improve the forecast of the terrestrial carbon cycle in tropical regions. The analysis is performed for five CO2 eddy covariance tower sites. Our results confirm an increasing Enhanced Vegetation Index (EVI) profile from the beginning to the end of the dry season, suggesting a higher photosynthetic capacity associated with emergence of new leaves. In addition, analysis of atmospheric contamination which could affect the indices and their interpretation, suggests that EVI is better suited than NDVI to study the vegetation dynamics in tropical forests, detecting more subtle changes. Moreover, EVI seasonal dynamics compared with meteorological data indicate that leaf phenology in tropical rainforest may be driven by availability of solar radiation. Future work to better evaluate atmospheric contamination (e.g. using MODIS Aerosol product) or the water stress in the dry season (using Normalized Differenced Water Index, NDWI) will be performed before integrating the 10-y phenology pattern into the ORCHIDEE global vegetation model (Krinner et al., 2005).