People who work in this field have a more advanced understanding than I do about drought, how and why it occurs, its frequency and severity, and the impact on natural and human worlds. This recognition brings us to a very interesting paper recently published in Scientific Reports, entitled Unprecedented drought over tropical South America in 2016: significantly under-predicted by tropical SST [sea surface temperature]. So, what did this paper show? 

Well, the Amazon region does encounter periodic droughts. There was one in 2005, another in 2010, both of which were 100-year events, and the most recent one in 2015-2016. The authors of this study, Amir Erfanian, Guiling Wang, and Lori Fomenko, all from the University of Connecticut, measured drought in three ways. They quantified the precipitation deficits and water storage on the ground. They also used two different vegetation measures of drought. The results showed that the most recent drought was unprecedented in severity.