Explaining annual streamflow variability of Amazonian rivers

Analysed in this study were the influence of El Nino events and the oscillation of the Intertropical Convergence Zone (ITCZ) on Amazonian rivers. Empirical orthogonal function analysis (EOF) was employed to quantify how much of the annual variability of Amazonian river discharges can be explained by El Nino events and anomalous ITCZ displacement. Normalized time series of the NINO 3.4 index and Atlantic Meridional Mode (AMM) index were analysed together with river discharge measurements at 13 sub-basins and longer reconstructed streamflow time series spanning over 60 years at four sites. The results show that the AMM index explains more of the streamflow annual variability than the NINO 3.4. The annual discharge variability of the rivers that drain from the south area of Amazonia (Xingu and Araguaia), were better explained by NINO3.4 than by AMM. However, a large part of the annual discharge variability of the Amazonian rivers remains to be explained by other phenomena not considered here.