Secondly, evaporation will increase due to the general warming, thus also reducing soil moisture. Two dynamical mechanisms may explain the lower dry season precipitation: (1) a stronger north-south tropical Atlantic sea surface temperature gradient (2) a general subtropical drying under global warming when the dry season southern Amazon is under the control of the subtropical high pressure.
First, a decline in precipitation of 24% in the southern Amazon lengthens the dry season and reduces soil moisture, despite of an increase in precipitation during the wet season, due to the nonlinear response in hydrology and ecosystem dynamics.
However, the periphery, notably the southern edge, is in danger of drying out, driven by two main processes. Our results suggest that the core of the Amazon rainforest should remain largely stable. To determine the likelihood and causes of such changes, we analyzed the output of 15 models from the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC/AR4) and a dynamic vegetation model VEGAS driven by these climate output. Recent climate modeling suggests that the Amazon rainforest could exhibit considerable dieback under future climate change, a prediction that has raised considerable interest as well as controversy. Future drying of the southern Amazon and central Brazil
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