Abstract ID: 488

Climatic and vegetation constraints on savanization of the Amazon

Insight into the vulnerability of ecosystems to changes in climate, in particular the possible trajectory of savanization in the Amazon is key to understanding the interaction of the Amazon with the Earth’s climate. We used a simple moisture-convection scheme for the Amazon to investigate the possibility of stable equilibria in the coupled land surface atmosphere system and analysed this with respect to carbon content and trajectory of vegetation by using the simple model results to force two dynamic vegetation models. Fundamental causes of different hydrological stable states of the vegetation atmosphere system can either be related to fundamental soil properties, such as field capacity and wilting point or atmosphere vegetation feedbacks. Either mechanism might be operating in the Amazon, when precipitation input is decreasing in such a way, that movement from the wet to the dry state may be occurring. However, which one of the two is operating has important and immediate consequences for restoration and preservation policies. We found that the existence of a alternate dry and wet state is dependent on the amount of evaporation from the surface and the magnitude of the convergence flux. Soil moisture memory generates some distinct hysteris in this relation, indication that it may be more difficult to regenerate from a dry state, once this has been initiated. We forced the two vegetation models , IBIS and LPJ with the climate of the moisture convection model and analysed the different vegetation and carbon trajectories associated with these stable states. Drier condition, and a sequence of drier below average years, show substantial decline in carbon content and the rise of grassland vegetation. We also performed some simple sensitivity analysis of these results to some key parameters such as variability of rainfall generation, rooting depth and soil type to show the robustness of our findings. The combined results give physically plausible trajectories for savanization and also give an indication what the key vegetation and atmospheric processes are that control savanization.

Session:  Feedbacks to Climate - Land cover, surface hydrology, and atmospheric feedbacks. (B)

Presentation Type:  Oral