The Strengthening of the Amazonian Precipitation in the Wet Season Driven by the Tropical SSTs Forcing

Amazonian rainfall plays a critical role in the global climate system and the hydrological cycle. It is thus important to quantify the changes of the Amazonian rainfall and clarify its mechanism. Previous studies indicate that the interannual variability of the Amazonian precipitation could be largely attributed to the variabilities in the South American monsoon and the El Niño/Southern Oscillation (ENSO). However, the trend of the wet season tropical Amazonian precipitation during the recent decades is less investigated. In this study, by combining both satellite and in-situ observations, it is revealed that the tropical Amazonian precipitation has been significantly increased by ~60 to 200mm (in different datasets) in the wet season during the satellite era from 1979 to 2015. We then use a state-to-the-art atmospheric model to simulate the impact of the tropical SSTs on the precipitation changes. Results show that the multidecadal warming of the tropical Atlantic contributes more than half of this precipitation change in the past three decades, while the east Pacific cooling plays a secondary role. We finally combine the simulation results and the reanalysis data to investigate the mechanisms of this process, i.e. the SST variability dramatically increases the convergence of the moisture transport over the Amazon region. The precipitation changes over the Amazon region largely impact on the local hydrological cycle and the ecosystem, and have important impacts on the global climate system through mediating the teleconnection between the Pacific and the Atlantic oceans. Our results show that the long-term change of the wet-season Amazonian precipitation is important and deserves further investigation and discussion.