A new NASA-funded study has revealed widespread reductions in the greenness of Amazon forests caused by last year's record-breaking drought, the U.S. National Aeronautics and Space Administration (NASA) said Tuesday in a statement.

The comprehensive study was prepared by an international team of scientists using more than a decade's worth of satellite data from NASA's Moderate Resolution Imaging Spectroradiometer and Tropical Rainfall Measuring Mission. Analysis of these data produced detailed maps of vegetation greenness declines from the 2010 drought.

The study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

"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," said Liang Xu, the study's lead author from Boston University. "It did not recover to normal levels, even after the drought ended in late October 2010."

The authors first developed maps of drought-affected areas using thresholds of below-average rainfall as a guide. Next, they 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 drought sensitivity of Amazon rainforests is a subject of intense study. Computer models predict a changing climate with warmer temperatures and altered rainfall patterns could cause moisture stress leading to rainforests being replaced by grasslands or woody savannas. This would release the carbon stored in rotting wood into the atmosphere, which could accelerate global warming. The United Nations' Intergovernmental Panel on Climate Change has warned similar droughts could be more frequent in the Amazon region in the future.