How green is the Amazon?

Not as green as it used to be, as shown in an analysis of satellite images made during last year’s record-breaking drought.

Because greenness is an indication of health in the Amazon, a decline in this measurement means this vast area is getting less healthy — bad news for biodiversity and some native peoples in the region.

What does a drop in the greenness index look like? It looks gold, orange and red in a graphic accompanying an article to be published in the journal Geophysical Research Letters:

Gray areas are the norm, based on a decade of satellite observations that cover every acre (actually every square kilometer) on the planet. Dots that are gold, orange or deep red show areas with a decrease in greenness. Scientists call this the Normalized Difference Vegetation Index (NDVI on this chart) or the greenness index.

The chart shows what happened during July, August and September of 2010, the height of the dry season — a deep loss of greenness. The researchers found that the 2010 drought reduced the greenness of approximately 965,000 square miles (2.5 million square kilometers) of vegetation in the Amazon, more than four times the area affected by the last severe drought in 2005.

Even when rains came in late October, greenness didn’t bounce back, according to Ranga Myneni, one of the scientists who worked on this research.

Drought stress in the Amazon, the world’s largest rainforest, is a subject of intense research. The American Geophysical Union said in a statement that a changing climate with warmer temperatures and altered rainfall patterns could change rainforests into grasslands or woody savannahs. This in turn would release the carbon stored in the rotting wood into the atmosphere, and could accelerate global warming.

The comprehensive study was prepared by an international team of scientists using data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measuring Mission (TRMM).

Graphic from article accepted by Geophysical Research Letters

Photo credit: REUTERS/Ricardo Moraes (Children play next to their floating house in Amazonas state, Brazil, November 4, 2010)

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