Publicações

The Amazon plays an important role in the functioning of the Earth’s climate. It acts as one ofthe critical heat sources for the global atmosphere via evaporation of water vapor at the surface and release ofheat in the middle and upper troposphere by latent heat of condensation in tropical convective clouds. Forest evaporation year-round is about 3 to 3.5 mID d-1 . In contrast, for savanna regions bordering the Amazon forest, evaporation is reduced during the dry season because of the limitation of soil moisture. Deforestation causes a large reduction in dry season evaporation. The cloudiness-rainfall regime of the undisturbed forest/is similar to that of a tropical ocean, which led us to call the Amazon Basin a “green ocean.” Biogenic volatile organic compounds are released by the forest into the atmosphere, where some play an important role in providing aerosols and cloudlcondensation nuclei. On the other hand, aerosols emitted by biomass burning may cause reduction of rainfall. Together the chapters in this section reveal a complex mix of interacting processes that acting in concert control the movement and composition of the atmosphere above Amazonia. Each separate study reveals some new insight into one facet, but together they reveal an integrated system in which change in one component will produce impacts in another. The most important message is that deforestation is not just a change in land use, but it impacts the functioning of the Amazonian ecosystem itself. Changes in the evaporation and the chemical composition ofthe atmosphere produce changes in the cloud physics and in the dynamics and thermodynamics of the atmospheric circulation. These, in tum, impact the rainfall and the hydrological cycle.