Impact of land use activity in the Amazon Basin evaluated

A new paper published January 18 in Nature reveals that human land use activity has begun to change the regional water and energy cycles -- the interplay of air coming in from the Atlantic Ocean, water transpiration by the forest, and solar radiation -- of parts of the Amazon basin. In addition, it shows that ongoing interactions between deforestation, fire, and climate change have the potential to alter carbon storage, rainfall patterns and river discharge on an even larger basin-wide scale. 

Cattle-pasture fire burning through the night in Mato Grosso, Brazil, the southern Amazon [Credit: Jennifer K. Balch, 2006]

The research was led by the Woods Hole Research Center (WHRC). Lead scientist Eric Davidson (WHRC) and 13 Brazilian and US colleagues from universities, government and the NGOs, all of whom participated in the Large-Scale Biosphere-Atmosphere Experiment in the Amazon (LBA), produced a framework by which the connections among climate change, agricultural expansion, logging, and fire risk can be 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. 

Co-author Jennifer K. Balch adds: "One strong sign of a new disturbance regime is the high number of recent large-scale wildfires, which are a by-product of intentional fires in Brazil's 'arc of deforestation.'" She emphasizes that these fires "are extremely frequent, occurring every few years, compared with every couple centuries in the past." 

Why is this important? Humans have been part of the Amazon basin forest-river system for thousands of years, but the expansion and intensification of agriculture, logging and urban development, and their synergistic impacts are beginning to stress the natural integrity of the ecosystem. 

Over 140,000 active fires were detected on a single day (08/23/2010) in this NASA MODIS image that spans 2500 km across southern Latin America, including Brazil, Bolivia, Argentina, Peru, Chile, and Paraguay (http://earthobservatory.nasa.gov/IOTD/view.php?id=45449) [Credit: Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC]

Since the Amazon River produces about 20% of the world's fresh water discharge and the Amazon forest holds about 100 billion tones of carbon (10 years' worth of global fossil fuel emissions), it is important that economic development in the region proceed along sustainable paths that do not 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," notes Dr. Davidson. "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. 

A map of the study area with related information. A thick blue line demarcates the hydrologic Amazon basin; isopleths of mean daily precipitation during the driest months of the year in mm are overlain onto four land-cover classes. The arrow emphasizes the trend from continuously wet conditions in the northwest to long pronounced dry seasons in the southeast. The scientists had to consider this natural trend and related information in their study on the interactions between global climate, land use, fire, hydrology, ecology and human activity [Credit: Paul A. Lefebvre]

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 km2 per year in 2004 to less than 7,000 km2 in 2010, but at the same time, the incidence of fire has not decreased, indicating continued risks for forest degradation through climate-fire interactions. 

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. 

Source: Woods Hole Research Center [January 18, 2012]