SAO PAULO, Brazil | Across the Amazon basin, river dwellers are adding new floors to their stilt houses, trying to stay above rising floodwaters that have killed 48 people and left 405,000 homeless.
Flooding is common in the world's largest remaining tropical wilderness, but this year the waters rose higher and stayed longer than they have in decades, leaving some fruit trees entirely submerged. Only four years ago, the same communities suffered an unprecedented drought that ruined crops and left mounds of river fish flapping and rotting in the mud.
Experts suspect global warming may be driving wild climate swings that appear to be punishing the Amazon with increasing frequency.
It's "the $1 million question," said Carlos Nobre, a climatologist with Brazil's National Institute for Space Research.
While a definitive answer will take years of careful study, climatologists say the world should expect more extreme weather in the years ahead. Already, what happens in the Amazon could be affecting rainfall elsewhere, from Brazil's agricultural heartland to the U.S. grain belt, as rising ocean temperatures and rainforest destruction cause shifts in global climate patterns.
"It's important to note that it's likely that these types of record-breaking climate events will become more and more frequent in the near future," Mr. Nobre said. "So we all have to brace for more extreme climate in the near future: It's not for the next generation."
The immediate cause of the unusually heavy rains across northern Brazil is an Atlantic Ocean weather system that usually moves on in March, but stayed put until May this year.
Almost simultaneously, southern Brazilian states far from the Amazon have suffered from an extended drought, caused by La Nina — a periodic cooling of waters in the Pacific Ocean. And La Nina alternates with El Nino, a heating up of Pacific waters that is blamed for catastrophic forest fires plaguing the Amazon in recent years.
"Something is telling us to be more careful with the planet. Changes are happening around the world, and we're seeing them as well in Brazil," President Luiz Inacio Lula da Silva said this month on his radio program.
Brazil's government approved $440 million in emergency funding in response to the northern floods and southern drought.
The drought is pushing up international commodity prices for soy, which used worldwide as animal feed and as a key additive in cereal, pasta and other processed foods. And the floods forced the planet's largest iron ore producer to shut down a key export railway for a week, slowing overseas shipments of the raw ingredient for steel.
"I think we should be preparing for this to become more the norm, and there's a need to look at what the future Amazon will look like," said Daniel Nepstad, a tropical forest ecologist and chief program officer for the Gordon and Betty Moore Foundation's environmental conservation program.
It is already grim for the poorest Amazon residents, the "ribeirinhos" (riverbank dwellers in Portuguese), many of whose families were drawn to the spongy land by the world's 19th-century rubber boom and have eked out a living since then.
The ribeirinhos are used to the rivers' rise and fall, and time their harvests to coincide with the end of the wet season, but this year the rains just didn't let up as they usually do in April. Thus bananas, beans, corn, manioc and watermelons lie ruined under the muddy water.
"Most people lost their crops and their cows, and the only thing they have left is their children and their homes," said Dorothea de Araujo, the Amazon operations manager for the international aid group World Vision, after touring an area where thousands were affected. "They want to rebuild, but they are scared of what will happen in the future."
The government is giving lumber seized from illegal Amazon loggers to the ribeirinhos so they can build their shacks higher.
The lumber also is going to slum dwellers whose stilt shanties litter big jungle cities such as Manaus — an industrial metropolis of 1.7 million that's also a jumping-off point for jungle tourism — so they can try to stay dry as the mighty Rio Negro, an Amazon River tributary, approaches a record high-water mark set in 1953.
The floods are driving anacondas and scorpions to higher ground and closer to humanity as they search for food. While many of the animals in the Amazon thrive on the higher water, experts warn that more droughts could sharply reduce the range of species such as pink Amazon River dolphins, already under pressure because of deforestation and pollution.
"We could be looking at an Amazon that is much more populated by animals that are generalists and can move through human landscapes, and some of the more sensitive species will be caught in islands of habitats," Mr. Nepstad said.
In Trizidela do Vale, floodwaters reached the red tile rooftops of many homes and left more than half of the town's 20,000 residents homeless. Many sheltered in cow pens used for the town's annual cattle fair until officials closed them as unsanitary.
In Manaquiri, ribeirinhos whose crops were destroyed paddle into the town of 19,000, seeking government handouts of food, medicine and clothing.
"We are used to floods and droughts and know how to coexist with them, but we are not used to them happening so swiftly and lasting so long and causing so much damage," said schoolteacher Gleicimeire Freire, who distributes aid with the Roman Catholic Church. "This is what is scaring us."
In southern Rio Grande do Sul state, bordering Argentina and Uruguay, many farmers say the driest weather in 80 years has withered their corn and alfalfa. Winter grass for cattle couldn't be planted, and milk production has suffered, said Darcisio Perondo, a congressman who represents the state.
"In some villages there wasn't enough water for people to drink, and in some towns they had to get water from the large rivers and tote it by truck for the cattle," Mr. Perondo said.
He called the situation a calamity, but isn't sure whether global warming is to blame.
"Anyone who reads the Bible knows that floods and droughts are cyclical," he said. "I just don't know if global warming is causing this."