Inter-hemispheric eco-climatic connections: The role of tropical forests in connecting the American monsoons

Abstract:

Vegetation structure and function are fundamental drivers of local and regional atmospheric dynamics. In the Amazon, for example, atmospheric destabilization associated with water and energy fluxes driven by vegetation, is recognized as a fundamental factor triggering the transition from dry to wet seasons. A recent study suggests that the transition season between the retreat of the North American monsoon system (NAMS) and the onset of its counterpart in South America (SAMS) has become longer since the early 90s. Such longer transition seasons are characterized by earlier retreats of the NAMS and delayed onset of the SAMS, with an associated delayed reversal of the cross-equatorial flow from Northern to Southern Hemisphere, and stronger surface convergence and convection over the equatorial Americas. Although large-scale features help to partially explain these changes, it is not clear whether recent large-scale vegetation changes in both continents could contribute to this observed disturbance. This work aims to identify the eco-climatic processes that could enable a possible influence of a longer and stronger dry season in the Amazon forests on the cross-equatorial flow and the demise of the NAMS. Addressing this possible inter-hemispheric link is key to understand future climate variability, and precipitation dynamics in tropical and subtropical Americas, especially at a time when the effects of anthropogenic forced change and conversion from Amazon forests to savannas become more dominant. The latter would be particularly relevant in order to understand the role of ecosystem changes on modulating climate variability over the Americas.