Two-way Feedbacks Between Tropical North Atlantic SST and Amazon River Basin Hydroclimatology at Seasonal and Interannual Timescales

Abstract:

The Amazon River basin (AM) is considered among the most critical tipping points of Earth’s climate system. At seasonal timescales, the hydroclimatic variability of AM is influenced by sea surface temperatures (SST) over the tropical Atlantic, by the dynamics of the Inter Tropical and South Atlantic Convergence Zones, and by land surface-atmosphere feedbacks. At interannual timescales, El Niño/Southern Oscillation (ENSO) is the main modulator of Amazonian hydroclimatology owing to teleconnections arising from the tropical Pacific and the tropical Atlantic, as well as by land surface-atmosphere feedbacks. Here we show statistical and physical evidences of the existence of two-way feedbacks between the TNA and AM regions at annual and interannual timescales, through lagged cross-correlation analysis of monthly series of the AM P-E index and TNA SST. The P-E index series are estimated with data from GPCC (P) and the ORCHIDEE model (E), and SST was obtained from ERSST v3b. The identified two-way feedbacks evidence that TNA SST influence the future AM hydrology, and that in turn AM hydrology influences the future TNA SST at both timescales (see Figure 1). The physical mechanisms and the time lags involved in the identified coupled dynamics are discussed using OLR data from NOAA, surface pressure gradient between TNA and AM (TNA-AM) and zonal winds velocities from the ERA-Interim Renalysis. Our results show that land-surface hydrological processes are not passive spectators but a key player of the large-scale ocean-atmosphere dynamics in the tropical Americas.