The Close Links between the Biological Functioning of Amazonia Forest and Climate (Invited Presentation)

Amazonia is a critical tropical region that is suffering large pressures from socioeconomic development as well as changes in climate. Over the last 30 years, knowledge about tropical forests have increase significantly with several large experiments such as the LBA (The Large Scale Biosphere Atmosphere in Amazonia), and field campaigns such as AMAZE-2008, GoAmazon 2014/15, ABLE-2A, ABLE-2B, and many others. Recently, deforestation is increasing, with about 7,000 Km² of forest converted to agricultural land in 2017. Climate is changing fast in Amazonia, as well as for the whole planet, increasing the pressure on ecosystems, especially tropical forests. Amazonia was a sink of atmospheric CO2 up to a few years ago, and right now, it is carbon neutral due to hydrological cycle changes and increase in climate extremes. It has been observed an intensification of Amazonian hydrological cycle, with increase of 30% in runoff at Óbidos in the last 30 years. Significant increase in climate extremes has also been observed, with stronger droughts and floods over the last 30 years. This makes an important stress for the ecosystem. The forest biology interacts strongly with atmospheric processes, releasing volatile organic compounds (VOCs) that produces large amounts of secondary organic aerosols (SOA) that are key to the cloud condensation nuclei (CCN) population and clouds formation and development. The forest has also important water vapor processing mechanisms trough complex soil-plant-atmosphere interactions. It is being recently observed that the dry season length is increasing by 6 days per decade, making a positive feedback on fires and deforestation.

The future of tropical forests, and Amazonia in particular, is depending on policies to preserve these key ecosystems, that could limit land use change for agricultural expansion. Another important risk is climate change, with observed increase in temperature already at about 1.5 degrees. Brazil has an ambitious target at its NDC under the Paris Agreement to reforest 12 million hectares till 2025. But deforestation in 2018-2019 is increasing to about 7,000-8,000 Km² deforested area per year.