Studying rainfall and flow trends is important to understand hydrological variability and
to determine what has influenced increases or decays. The present study analyzes the
trends of the space-time annual series of precipitation (total annual precipitation and
maximum annual precipitation) and flow (averages, maximums and minimums) in the
Amazon River Basin through non-parametric Mann-Kendall and Sen's tests. Slope for
five different periods (1975-2014, 1980-2014, 1985-2014, 1995-2014 and 2000-2014).
The results indicate that the series of average flows are increasing in the Amazon
Basin for all analyzed periods. In the sub-basins of the right bank of the Amazon River,
Tapajós and Madeira, the most recent period (2000-2014) registered the greatest
trends of increase in the average annual flow from 1998 (year of strong El Niño) and
that reached the largest values already observed. In the maximum flow series, the
Óbidos station had an increasing rate of increase for the five periods analyzed for
extreme flood events, which directly affect the population residing in these areas. Mean
flow decay trends were found at six stations in the Tapajós and Madeira sub-basins.
As for precipitation, there are significant trends of increase and decay distributed in
several distinct regions of the basin. The stations with the highest positive precipitation
trends had a significant increase since 1997, reaching the highest peaks in 2013. The
comparison of the magnitude of the trends by the Sen's Slope test shows that there is
a behavior of increasing flow rates in the entire Amazon basin and in terms of
precipitation there are areas of increase and decrease, that is, precipitation is not the
only variable that influences the flows of the Amazon River basin.
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