In São Paulo, Brazil, which is suffering its worst drought in almost a century, Maria de Fátima dos Santos has lived for days at a time with no water, relying on what she had carefully hoarded in bottles.

But in the Bolivian Amazon, about 1,800 miles (2,897 kilometers) away, Nicolás Cartagena recalls the day almost a year ago when floodwaters rose to the thatched rooftops of Indian communities, destroying crops and washing away homes.

The drought in South America's biggest city and the flooding in the Amazon are being triggered by the same wind-driven weather phenomenon that scientists say is probably a harbinger for more extreme water shortages and flooding across the continent.

No one fully understands this boom-and-bust cycle, but meteorologist José