Abstract

Rainfall variability over the Amazon basin has often been linked to variations in the Pacific sea surface temperature (SST), in particular, the El Nio Southern Oscillation (ENSO). However, only a fraction of the Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng et al. (2008), here we suggest an influence on Amazon rainfall estimation from the subtropical North Atlantic Ocean. The strength of this influence is comparable to the better-known Pacific ENSO connection. Our analysis of satellite-based precipitation data for the period of 1979-2006 shows that a combination of Nio-3.4 and North Atlantic explains 53% of Amazon rainfall variability, with 25% from Nio-3.4, 20% from North Atlantic. The Atlantic influence is strongest in the southwestern part of the Amazon basin, due to changes in the local Hadley circulation and the movement of ITCZ following anomalous SST. This Atlantic correlation is highest during the Amazon dry season (boreal summer and autumn) when the hydro-ecosystem is most vulnerable as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the future change of the Amazon rain forest.
Recent climate and vegetation modeling suggest that the Amazon rain forest could exhibit considerable dieback during the coming century as a result of global climate change (Cox et al. 2000), a prediction that has raised considerable interest as well as controversy. In order to test these conclusions, and to determine the likelihood and cause of such changes, we analyzed the output of 15 models from the Intergovernmental Panel on Climate Change Forth Assessment Report (IPCC AR4) and results from a dynamic vegetation model VEGAS forced by these climate output. Our results suggest that the core of the Amazon rain forest should remain largely stable. However, the periphery, notably the southern edge, is in danger of drying out towards the end of this century. In this research, possible mechanisms behind this drying in the Southern edge of Amazon basin are investigated. Because the southern Amazon is also under intense human influence, the double pressure of deforestation and climate change may subject the region to dramatic changes in the 21st century.

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