SENSITIVITY OF SIMULATED SURFACE FLUXES TO CHANGES IN LAND-SURFACE PARAMETERIZATIONS - A STUDY USING ABRACOS DATA

The simplified Simple Biosphere model(SSiB) has been validated using o bserved meteorological, turbulent flux, and vegetation property data f rom the Anglo-Brazilian Amazonian Climate Observation Study (ABRA-COS) over a forest clearing site. The results show that SSiB is able to si mulate the observed fluxes realistically. The differences between the simulated and observed latent and sensible heat fluxes are less than 1 0 W m(-2). Compared to previous deforestation experiments, the new veg etation dataset produces significantly different latent heat fluxes an d surface temperatures in off-line and general circulation model (GCM) simulations. Using the new dataset, the GCM simulated surface tempera ture is about 2 K higher, and the simulated latent heat flux is about 25 W m(-2) lower than that generated using a previous dataset. These d ifferences can be expected to result in substantially different respon ses in rainfall and atmosphere circulation. The parameters that are mo st significant in producing such large differences are leaf area index and soil properties. This study again demonstrates that to realistica lly assess the climatic impact of land surface degradation a realistic specification of the land surface conditions within GCMs is crucial.