Amazon forest becoming less green

Posted by Kate Taylor

Satellite data is revealing an Amazon rainforest that's decidedly less green than usual, showing the catastrophic effects of 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," says study lead author Liang Xu of Boston University.

The study was based on more than a decade's worth of satellite data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measuring Mission (TRMM).

The authors developed maps of drought-affected areas using thresholds of below-average rainfall as a guide, and then identified affected vegetation using two different greenness indexes as surrogates for green leaf area and physiological functioning.

The maps show the 2010 drought reduced the greenness of approximately 965,000 square miles of vegetation in the Amazon - more than 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," says Arindam Samanta of Atmospheric and Environmental Research.

The severity of the 2010 drought was also seen in records of water levels in rivers across the Amazon basin. These show last year to have been the driest year on record based on 109 years of Rio Negro water level data at the Manaus harbor.

Continuing Amazonian droughts could have severe effects on the planet.
Computer models predict that moisture stress could cause some of the rainforests to be replaced by grasslands or woody savannas. This would release the carbon stored in the rotting wood into the atmosphere, and could accelerate global warming.