Rivers in the Amazon region are veins of life - they act as roads for forest communities, as home for fish and other water creatures, and as gathering spots where locals bathe and children play.

But in October 2015, water levels in the Negro River - near Manaus, the capital of Brazil's state of Amazonas - decreased so much that boats were left stranded. Less intense rainfall and strong heat were behind the river's lower levels.

"Low rivers in the Amazon result in total chaos," says Jose Marengo, a climatologist and hydrologist, and member of the Intergovernmental Panel on Climate Change established by the United Nations.

"Over the past 10 years in the Amazon, we had two hundred-year droughts, and two hundred-year floods," Marengo told DW. "Those phenomena that are supposed to happen once every 100 years are now happening much more often."

Mataripe Trumai, who lives in the midsection of the Xingu River in Brazil's Amazonas, says "climate change alters everything." He explains how fish are disappearing, rivers are being silted up, and even a yellow fruit that the fish eat is not available as it was before.

Weather has been changing in the village of Mundurukus, on the Cururu River in Brazil's Amazonas

"The elders say that even the rain does not come at the right time. That the thunder is getting stronger. And the lightning too," Mataripe Trumai says.

And what will happen to this already changing scenario, if global temperature rises by 3 degrees Celsius (5.4 degrees Fahrenheit) by the end of the century, compared to pre-industrial levels?

Rising rivers despite longer dry seasons

For Paulo Artaxo, professor at the Institute of Physics of the University of Sao Paulo, before speaking of the future, one needs to talk about the present. There are two aspects to the Amazon's climatology currently drawing researchers' attention.

On the one hand, he says, there's an intensification of the hydrological cycle in the Amazon. The flow of the Amazon River in Obidos, near its mouth between Santarem and Belém in the Brazilian state of Para, has been rising slowly over the last 20 years, and water levels there are up 15 percent.

"The question is attribution. Is this caused by global [climate] change or not?" Artaxo asks. "No one knows this answer."

Climatologists are studying why river levels have increased in some areas of the Amazon region over past decades

The second change is the longer dry season in the western region. "The dry season has already increased by two weeks," Mr. Artaxo explains. "Before, it lasted three-and-a-half to four months - now, the dry season is increasingly longer."

Artaxo points out that the longer dry season may be a natural fluctuation - or it may be a reflection of global climate change. He notes that the sharp drop in deforestation, to 5,000 square kilometers (2,000 square miles) in 2014 from 27,000 square kilometers (10,400 square miles) in 2005, is very important.

'Victim and executioner'

While data for the Amazon region is still lacking, Brazilian scientists are now conducting more accurate studies.

Brazil has just started a project with the British government to research the impacts of increasing temperatures in the Amazon. One of those may be fire.

"What we think is that with [global] warming at 3 degrees or 4 degrees Celsius, the forest could collapse," Artaxo says.

"If this happens, there are hundreds of billions of tonnes of CO2 that are concentrated in the trees and can be expelled to the atmosphere," he points out.

That is why it is said that Amazon is both victim and executioner.

Sonia Guajajara, executive coordinator of association Apib - which represents indigenous people in Brazil - says climate change impacts are especially strongly felt on indigenous lands.

Indigenous people who continue to live close to the land are more directly affected by environmental changes

For example, for six weeks until the end of October 2015, indigenous Arariboia land was site of a nonstop fire in the state of Maranhao, in northeastern Brazil.

"The fire spread and burned 53 percent of 413,000 hectares," Guajajara says. "Everyone complains a lot about how much the plantation has changed," she added.

Indigenous climate diary

At the COP21 United Nations climate summit held in Paris, indigenous people who live on the banks of the Negro River presented a simple and innovative research project that allows the monitoring of river levels, rain and other changes happening in the region.

For eight years, many indigenous people in the region took daily notes of when there were sunny or rainy days; or if there were fruit and flowers.

Indicators they looked at included river levels, the constellations, rain in the region, and the seasons - according to their own culture. This created a climate calendar that has little to do with the Gregorian one.

The Social Environmental Institute, in partnership with the database InfoAmazonia, at the Paris conference launched an indigenous calendar of the Tiquie River's cycles.

Indigenous people have a direct sense of ongoing weather changes

'Quiet period'

The calendar was inspired by the indigenous people's perception that things were no longer happening accordingly to the wisdom of shamans. Fruits and plants were no longer growing at the expected time, and fish were also disappearing.

Andre Baniwa, who came to Paris from the northwestern Amazon, said to his people that a time of silence is approaching in the world.

"The shamans of the Baniwa people say this world will shut down in a while, and there will be no sign of life," says the leader Baniwa. "It will be a quiet period."