In May and June, heavy rain pushed Brazil's sprawling Negro River to its highest level in more than a century, causing flooding in Manaus, the Amazon rainforest's largest city.

At the same time, parts of southern and west-central Brazil in the Parana River basin — including Brazil's largest city of Sao Paulo — have suffered unprecedented drought due to low rainfall.

The disastrous mix of floods, drought and intense downpours could be a glimpse of a potentially dire future as a heating planet and surging deforestation alter long-standing weather patterns throughout Brazil and South America, scientists warn.