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Climate change and moisture recycling in the Amazon

A river flows through the Amazon Rainforest.

A river flows through the Amazon Rainforest. Image by Rhett A. Butler/Mongabay.

  • Mongabay is publishing a new edition of the book, “A Perfect Storm in the Amazon,” in short installments and in three languages: Spanish, English and Portuguese.
  • Author Timothy J. Killeen is an academic and expert who, since the 1980s, has studied the rainforests of Brazil and Bolivia, where he lived for more than 35 years.
  • Chronicling the efforts of nine Amazonian countries to curb deforestation, this edition provides an overview of the topics most relevant to the conservation of the region’s biodiversity, ecosystem services and Indigenous cultures, as well as a description of the conventional and sustainable development models that are vying for space within the regional economy.
  • This is part of chapter 1 of “A Perfect Storm in the Amazon,” see the bottom of this page for links to all the excerpts.

Starting in the 1990s, ecosystem ecologists and atmospheric scientists in the Brazilian space agency embarked on a sophisticated collaboration with NASA and other international research institutions; their goal was to understand and model the interactions between the atmosphere, the ocean and the forest ecosystem.

They collected data using instruments mounted on satellites, airborne platforms and canopy towers, a collaboration that discovered how cyclical anomalies in ocean temperatures, such as El Niño/La Niña, drive the decadal-scale droughts and floods that impact the Amazon. Their most important finding was to elucidate how tropical forests recycle water between the surface and the upper troposphere via a process known as ‘deep convection’; sometimes referred to as a ‘biotic pump’; this natural system maintains the high precipitation that defines the Amazon rainforest.

The South American Monsoon is established and controlled by the rotation of the Earth, the seasonal shift of the Inter Tropical Convergence Zone (ITCZ), the height of the Andes, and atmospheric pressure gradients driven by temperature differences across the South American land mass. Data source: Marwan, N. and J. Kurths. 2015. ‘Complex network based techniques to identify extreme events and (sudden) transitions in spatio-temporal systems’. Chaos: An Interdisciplinary Journal of Nonlinear Science 25 (9): 097609.

The impacts of deforestation, forest fragmentation and forest degradation are all weakening water recycling, and this is enhancing the intensity and frequency of seasonal and interannual drought. The risk is particularly acute in the Southern Amazon, a climatic transition zone where subtle shifts in ecological succession can determine whether a landscape is dominated by forest or savanna species. When and if a forest community is established, feedback mechanisms will reinforce the biotic pump, which favors an equilibrium state that supports the maintenance of rainforest. A rapid transition to a non-forest equilibrium can occur if a key environmental factor, such as drought, wildfire or logging, passes a threshold that alters the microclimate that favors forest species. When that occurs, rainforest trees suffer high rates of mortality and are replaced by species adapted to open savanna-like conditions.

Wildfires typically start when landholders burn pasture to renew forage or clear forest to establish new fields; managed fire often spreads into adjacent natural forest and, during drought years, can damage millions of hectares of primary forest habitat. This photograph of wildfires along the Río Xingu was taken by astronauts from the International Space Station in 2011. NASA Earth Observatory,

Climate models show that drought in the Amazon will become both more frequent and intense, while higher temperatures increase stress on tropical trees. There is increasing concern that the Southern Amazon could suffer from two or more consecutive years of drought, which could trigger a large-scale forest dieback of cataclysmic proportions. Known as the ‘tipping point hypothesis’, it is a clarion call of the dangers from uncontrolled deforestation, illegal logging and the indiscriminate use of fire by small farmers and ranchers. The impact of a collapsing forest ecosystem would extend well beyond the loss of biodiversity in the remnant forest of the Southern Amazon because it would signal a dramatic reduction in rainfall across the region – and beyond.

The most economically significant discovery of recent years grew out of a collaboration between meteorological agencies to integrate the subregional manifestations of the annual wet and dry seasons into a common continental-scale climate system. Christened the South American Monsoon (SAM), it mediates the flow of water from the Atlantic Ocean westward across the Amazon, south along the base of the Andes and, eventually, southeast into the subtropical landscapes of Bolivia, Paraguay, Central Brazil and Northern Argentina. The combination of the water recycling driven by deep convection within the Amazon and the distribution of water across the continent by the SAM directly links the productivity of one of the planet’s most important bread baskets – and the economic health of four nations – with the conservation of the Amazon rain forest.

“A Perfect Storm in the Amazon” is a book by Timothy Killeen and contains the author’s viewpoints and analysis. The second edition was published by The White Horse in 2021, under the terms of a Creative Commons license (CC BY 4.0 license).

Read the other excerpted portions of chapter 1 here:

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