Quirky Winds Fuel Brazil's Devastating Drought, Amazon's Flooding Boom-and-bust water phenomenon could become a new normal in South America, scientists say.

http://news.nationalgeographic.com/news/2015/02/150226-drought-floods-south-america-brazil-bolivia-flying-rivers-environment/

The loop starts in the Atlantic Ocean, where the winds carry moisture westward over the Amazon. Some falls as rain, but as the air passes, it also absorbs moisture from trees. When these "flying rivers" hit the Andes, they swing south, showering rain over crops and cities in eastern Bolivia and southeastern Brazil.

Beginning a year ago, however, a phenomenon called "atmospheric blocking" transformed that wind pattern. Marengo, a senior scientist at the Brazilian National Center for Early Warning and Monitoring of Natural Disasters (CEMADEN), likens this to a giant bubble that deflected the moisture-laden air, which instead dumped about twice the usual amount of rain over the state of Acre, in western Brazil, and the Bolivian Amazon, where Cartagena lives.

At the same time, cold fronts from the south, which cause precipitation over São Paulo and Rio de Janeiro, were shunted aside, and as the system lingered, the drought took hold, Marengo said in an interview.

Such prolonged events may be unusual, but they are not unheard of.