Climate experts say the region is reeling from the effects of El Niño, the cyclical climate phenomenon that can bring heavy rains to Brazil’s southern regions while causing drought in the Amazon rainforest.

But the effects of El Niño have been exacerbated by a mix of climate change, deforestation and haphazard urbanization, according to Mercedes Bustamante, an ecologist and professor at the University of Brasília.

“You’re really looking at a recipe for disaster,” said Dr. Bustamante, who has written several reports for the Intergovernmental Panel on Climate Change, a body of experts convened by the United Nations.