Future deforestation in the Amazon and consequences for South American climate

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 savannah 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 (EDBRAMS) we investigate the expected impacts of predicted future land use on the climate of South America. The climate response in the model simulations is generally consistent with expectations from previous global modeling simulations with drier conditions resulting from deforestation, however the changes in precipitation are relatively small (on order of a few percent). Local drying is driven primarily by decreases in evapo-transpiration associated with the loss of forest, and concomitant increases in runoff. Significant changes in convectively available potential energy (CAPE) and convective inhibition (CIN) during the transition to the wet season indicate that the decrease in surface latent heat flux is indeed leading to a drier atmosphere, however these changes occur around a mean climatological state that is already very favorable for convection, and thus lead to relatively small changes in precipitation. If, however, these land use changes were to occur under a background state of drier conditions, such as those predicted for the future global climate model experiments, this additional atmospheric drying may be sufficient to decrease precipitation more substantially.