Amazon basin shows signs of stress

UC SANTA BARBARA (US) — Human land-use activity has begun to change the regional water and energy cycles of parts of the Amazon basin.

A new study published in the journal Nature also shows ongoing interactions of deforestation, fire, and climate change have the potential to alter carbon storage, rainfall patterns, and river discharge on an even larger scale.


More than 140,000 fires were detected on Aug. 23, 2010, in this NASA image that spans 2,500 kilometers across southern Latin America, including Brazil, Bolivia, Argentina, Peru, Chile, and Paraguay. (Credit: Jeff Schmaltz, NASA)

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Led by scientists at the University of California, Santa Barbara and Woods Hole Research Center, the work involved researchers from 13 Brazilian and U.S. universities, and government and non-governmental organizations. Their investigations produced a framework by which the connections among climate change, agricultural expansion, logging, and fire risk were evaluated.

The framework considers changes in greenhouse-gas emissions, and energy and water cycles. Using it, they found signs of transition to a disturbance-dominated regime in the southern and eastern portions of the Amazon basin.

“One strong sign of a new disturbance regime is the high number of recent large-scale wildfires, which are a byproduct of intentional fires in Brazil’s ‘arc of deforestation’,” says  Jennifer K. Balch, a postdoctoral associate at UC Santa Barbara and co-author of the study. “These fires are extremely frequent, occurring every few years, compared with every couple centuries in the past.”

Why is this significant? Humans have been part of the basin forest-river system for thousands of years. But since the Amazon River produces about 20 percent of the world’s fresh water discharge, and the Amazon forest holds about 100 billion metric tons of carbon (10 years’ worth of global fossil fuel emissions), it is important that economic development in the region proceed along sustainable paths that don’t degrade the ecosystem services provided to local, regional, and global communities by the forests and rivers of the region.

“The studies in this review document changes in river flow, sedimentation in rivers, and lengthening of the dry season in the southern and eastern flanks of the Amazon Basin,” says lead scientist Eric Davidson of the WHRC.

“Whether similar changes are likely to occur in other parts of the basin will depend on the interplay of management decisions and the impacts of climate change during the next few years and decades.”

The project showed that the Amazon forest is resilient to considerable climatic variation from year to year, but that this resilience can be exceeded by severe or prolonged drought.

The evidence points to a system in biophysical transition, highlighting the need for improved understanding of the trade-offs among land cover, carbon stocks, water resources, habitat conservation, human health, and economic development in future scenarios of climate change and land-use change.

Efforts in Brazil to curb deforestation have led to a significant decline in the clearing of forests in the Amazon basin, from nearly 28,000 square kilometers per year in 2004 to less than 7,000 square kilometers in 2010; but, at the same time, the incidence of fire has not decreased, indicating continued risks for forest degradation through climate-fire interactions.

“In 1997-98, during the drought associated with an El Niño event, 39,000 square kilometers of intact Amazon forest burned,” Balch says. “That’s twice the area annually deforested in Brazil between 1988-2005.”

With Brazil poised to become a major economic power, the study emphasizes that improvements in scientific and technological capacity, and human resources will be required to guide and manage future sustainable development in the region.

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