March 29, 2011
Amazon Losing Its Green Flare After 2010 Drought
A new study funded by NASA has found that Amazon forests are losing their greenness due to last year's record-breaking drought.
"The greenness levels of Amazonian vegetation -- a measure of its health -- decreased dramatically over an area more than three and one-half times the size of Texas and did not recover to normal levels, even after the drought ended in late October 2010," Liang Xu of Boston University and the study's lead author said in a statement.
Researchers used computer models to predict that climate change could cause some of the rainforests to be replaced by grasslands or woody savannas. This change would release carbon stored in the rotting wood into the atmosphere, which could inevitably accelerate global warming.
An international team of scientists used over a decade's worth of satellite data from NASA's Moderate Resolution Imaging Spectroradiometer and Tropical Rainfall Measuring Mission.
The team used these instruments to produce detailed maps of vegetation greenness declines from the 2010 drought.
The researchers first developed maps of drought-affected areas using thresholds of below-average rainfall as a guide. They then identified vegetation using two different greenness indexes as surrogates for green leaf areas and physiological functioning.
The maps found that the 2010 drought reduced the greenness of about 965,000 square miles of vegetation in the Amazon, which is over four times the area affected by the last severe drought in 2005.
"The MODIS vegetation greenness data suggest a more widespread, severe and long-lasting impact to Amazonian vegetation than what can be inferred based solely on rainfall data," Arindam Samanta, a co-lead author from Atmospheric and Environmental Research Inc. in Lexington, Mass, said in a statement.
The 2010 drought brought record water levels in rivers across the Amazon basin, including the Rio Negro.
"Last year was the driest year on record based on 109 years of Rio Negro water level data at the Manaus harbor. For comparison, the lowest level during the so-called once-in-a-century drought in 2005, was only eighth lowest," Marcos Costa, coauthor from the Federal University in Vicosa, Brazil, said in a statement.
The team also used the NASA Earth Exchange (NEX) in their research. The scientists used NEX to obtain a large-scale view of the impact of the drought on the Amazon forests.
"Timely monitoring of our planet's vegetation with satellites is critical, and with NEX it can be done efficiently to deliver near-real time information, as this study demonstrates," study coauthor Ramakrishna Nemani, a research scientist at Ames, said in a statement
The study will be published in Geophysical Research Letters, which is a journal of the American Geophysical Union.
Image 1: NASA satellite sensors, such as MODIS, showed an average pattern of greenness of vegetation on South America: Amazon forests which have very high leaf area are shown in red and purple colors, the adjacent cerrado (savannas) which have lower leaf area are shown in shades of green, and the coastal deserts are shown in yellow colors. Image Credit: Boston University/NASA
Image 2: Red and orange identify areas where satellite measurements indicated reduced Normalized Difference Vegetation Index (first index of greenness) of the Amazon forest during the 2010 drought. Image Credit: Boston University/NASA
Image 3: Red and orange identify areas where satellite measurements indicated reduced Enhanced Vegetation Index (second index of greenness) of the Amazon forest during the 2010 drought. Image Credit: Boston University/NASA
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