Future Deforestation in the Amazon and Consequences for South American Climate

Abstract:

Ongoing agricultural expansion in Amazonia and the surrounding areas of Brazil is expected to continue over the next several decades as global food demand increases. The transition of natural forest and cerrado ecosystems to pastureland and agricultural crops is predicted to create warmer and drier atmospheric conditions than the native vegetation. Using a coupled ecosystem- regional atmospheric model (ED-BRAMS) we investigate the impacts of predicted future land use on the climate of South America. We find that the climate response in our model is consistent with expectations - with drier conditions resulting from deforestation, however the changes in precipitation are moderate. Local drying is driven primarily by decreases in evapotranspiration associated with the loss of leaf area, and coincident increases in runoff. Significant consistent changes are seen in convectively available potential energy and convective inhibition suggesting that the decrease in surface latent heat flux is indeed leading to a drier atmosphere, however these changes occur at mean state values that are already very favorable for convection leading to little change in precipitation. If large-scale circulation changes occur in the future to push the atmosphere over the Amazon towards a drier state as predicted by the CMIP3 and CMIP5 archives, we postulate that land use change could accelerate the movement across a convective threshold.