Impact of Drought in the Amazon Delta on Global Warming

The Great Lake of Manacapuru (the light coloured part is normally covered by water), community Dominguinho, region which was isolated from its municipality Caapiranga - west of Manaus. Photo Eduardo Nicolau/AE

Brazilian and British scientists conclude that the drought in the Amazon delta in 2010 was worse than the “drought of the century” in 2005, and may have had a bigger impact on global warming than what the United States provoke in one year,.
The survey was conducted in partnership between the British universities of Leeds and Sheffield and the Instituto de Pesquisa Ambiental da Amazônia (IPAM = Institute for Amazonian Environmental Research).

An increased frequency of droughts as the ones in 2005 and 2010 threatens to turn the world’s largest tropical forest, from a sponge that absorbs, into a source of greenhouse gases, accelerating global warming. This is because the trees normally absorbing carbon dioxide as they grow, helping to cool the planet, release these gases when they die and rot.

Map shows how in 2010 the deficit of water, compared to the year average without severe drought, was higher in 2010 than in 2005 - the dark spots indicate greater deficit. (Photo: Reprodução)

“If such events occur more frequently, the Amazon forest would reach a point where, from a valuable store of carbon, reducing the speed of climate change, it changes into a large source of greenhouse gases, which could accelerate global warming”, Simon Lewis, an ecologist at the University of Leeds, said.

The study, published in the Science, shows that last year’s drought caused a reduction of rainfall in an area of 3 million square kilometres of forest – far more than the 1.9 million square kilometres affected in 2005.

In addition to be much broader, the drought of 2010 was also more intense, causing increased tree mortality, with three major epicentres. The 2005 drought hit mainly the south-western Amazonia.

A boat sitting on a dry bed in the middle of the Rio Negro, in front of Manaus

Because of this, the study said, the Amazon forest will no longer absorb in 2010 and 2011 its usual volume of 1.5 billion tons of carbon dioxide from the atmosphere. Moreover, the dead and dying trees will release 5 billion tons of gas over the next year, causing the cumulative impact to reach 8 billion tons.

In 2009, for comparison, the USA emitted 5.4 billion tons of carbon dioxide by using fossil fuels

Emissions caused by the two droughts were probably sufficient to cancel all of the carbon absorbed by the Amazon forest in the last ten years, the study said.

Vicious Circle
The last year’s drought emptied major rivers in the Amazon delta and isolated thousands of people in riverside communities. It caused perplexity as scientists had estimated that a drought like that of 2005 would only occur every hundred years.

Both droughts so intense in such a short time, however, fit the predictions of some climate models about the Amazon forest in this century. Droughts make it more prone to forest fires, which in turn affects their ability to regenerate.

Under the more extreme scenarios of these models, large parts of the Amazon can become cerrado (savannah) by mid-century, with a strong reduction of its animal and botanical biodiversity.

Although deforestation caused by human activity has fallen sharply in Brazil in recent years, scientists say the forest is still very vulnerable.

A crucial element is whether the droughts were caused by the increased concentration of greenhouse gases in the atmosphere or whether they are an anomaly. If they are the result of global warming, a vicious circle of higher temperatures and droughts, the forest as a whole could fade over the coming decades, with an Amazon much drier, with less forest.

Read also my article: “Climate Change and Evolution – The Amazônia”