NASA Satellites Detect Extensive Drought Impact On Amazon Forests

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.

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 (MODIS) and
Tropical Rainfall Measuring Mission (TRMM). 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 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 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," said Arindam Samanta, a
co-lead author from Atmospheric and Environmental Research Inc. in
Lexington, Mass.

The severity of the 2010 drought also was seen in records of water
levels in rivers across the Amazon basin, including the Rio Negro
which represents rainfall levels over the entire western Amazon.
Water levels started to fall in August 2010, reaching record low
levels in late October. Water levels only began to rise with the
arrival of rains later that winter.

"Last year was the driest year on record based on 109 years of Rio
Negro water level data at the Manaus harbor," said Marcos Costa,
co-author from the Federal University in Vicosa, Brazil. "For
comparison, the lowest level during the so-called once-in-a-century
drought in 2005 was only eighth lowest."

As anecdotal reports of a severe drought began to appear in the news
media last summer, the authors started near-real time processing of
massive amounts of satellite data. They used a new capability, the
NASA Earth Exchange (NEX), built for the NASA Advanced Supercomputer
facility at the agency's Ames Research Center in Moffett Field,
Calif. NEX is a collaborative supercomputing environment that brings
together data, models and computing resources.

With NEX, the study's authors quickly obtained a large-scale view of
the impact of the drought on the Amazon forests and were able to
complete the analysis by January 2011. Similar reports about the
impact of the 2005 drought were published about two years after the fact.

"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," said study
co-author Ramakrishna Nemani, a research scientist at Ames. An
article about the NEX project appears in this week's issue of Eos,
the weekly newspaper of the American Geophysical Union.

For more information about this study and the NEX project, visit:

https://c3.ndc.nasa.gov/nex/projects/1209/

For more information about the MODIS sensor and data products, visit:

http://modis.gsfc.nasa.gov

For information about the Tropical Rainfall Measuring Mission, visit:

http://trmm.gsfc.nasa.gov

Source: NASA

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