Inter-annual variability of some river stream-flows and rainfalls in the Amazon basin

Abstract

For four locations (Samuel, 9° S, 63° W; Balbina, 1° S, 59° W; Curua-Una, 13° S, 54° W; Tucurui, 4° S, 50° W) in the Amazon, the river stream-flows (RSF) were maximum during March, April and/or May and minimum during September-October, while rainfalls in similar areas had maximum earlier, in January-March. There were considerable year-to-year fluctuations, not always similar at all the locations. An examination of the two largest El Niño events (1982-83 and 1997-98) showed some effects at some locations during intervals when the El Niños were active, but some effects were seen even outside these active intervals. Some RSFs showed relationship with South Atlantic SST. A spectral analysis showed that ENSO indices had prominent periodicities at 7-9, ~6 years and QTO (Quasi-triennial oscillation, 3-4 years) and not so prominent periodicities in the QBO (Quasi-biennial oscillation, 2-3 years). These were only partially reflected in some RSFs. There is an indication that some hydrological QBOs may be related to stratospheric wind QBO. Besides QBO and QTO, the RSFs had significant periodicities in 7-14 years range, ~22 years and ~55 years. Long-term trends (23-year running means) were not linear and showed oscillations of ~0.2%, grossly dissimilar at the different locations.