News Release [PDF]
April 5, 2004
Contact Dr. Gregory Asner at Carnegie's Department of Global Ecology, 650-462-1047
x 202, gasner @ globalecology . stanford . edu
Amazon drought now measured from space
Stanford, CA. Using a unique combination of ground-based and space-based tools,
scientists have determined for the first time how drought conditions, and possibly carbon
uptake, in the Amazon rainforest can be quantified over large forest areas from space.
The results are published in the on-line early edition of the Proceedings of the National
Academy of Sciences, April 5-9.
"Understanding the Amazon environment is an essential puzzle piece needed to
understand how the biosphere interacts with the climate system," said lead author Dr.
Gregory Asner of the Department of Global Ecology at the Carnegie Institution* in
Stanford, California. "The Amazon is simply too big and complex to study on the ground
alone," he continued. "Thus far it's been impossible to determine some of the most basic
properties of the forest that we need in order to understand what happens during common
climatic events--such as the El Niño dry periods--and what that means to forest growth
and the amount of carbon that is locked up in the forest via photosynthesis. Without these
measurements we will fall short in understanding how large a role tropical forests play in
mediating the effects of fossil-fuel emissions from human activities."
Amazonia, the world's largest rainforest, experiences a big range in rainfall from the
rainy to dry seasons and during global climatic events such as El Niño. The amount of
precipitation affects forest dynamics, land use, and fire susceptibility. To evaluate
drought conditions the researchers conducted the first forest canopy experiment in the
region. They covered over 10,000 square meters of the central Brazilian Amazon forest
with plastic making a "drydown" site and then measured rainfall, soil moisture, leaf and
canopy characteristics over time. They coupled these data with a new space-based
technology called imaging spectroscopy from the NASA Earth Observing-1 (EO-1)
satellite launched in November of 2000. They found that the spectra collected by the
satellite from reflected sunlight correlates with on-ground measurements indicating a
decrease in soil water and dehydrated leaves.
"The fact that we confirmed that satellite imaging can be used to measure something as
detailed as the physiology of the rainforest canopy, means that this technique might be
useful for understanding other types of ecological phenomena at both large and small
scales," Asner remarked. " We believe that space-based technology like this is the wave
of the future for analyzing our planet, " he concluded.
*Other authors include Daniel Nepstad (Woods Hole Research Center and Instituto de
Pesquisa Ambiental da Amazonia, Belém, Brazil), Gina Cardinot ( Instituto de Pesquisa
Ambiental da Amazonia), and David Ray ( Woods Hole Research Center). This study
was supported by NASA, The Mellon Foundation, and the Carnegie Institution.
The Carnegie Institution of Washington (www.CarnegieInstitution.org) has been a
pioneering force in basic scientific research since 1902. It is a private, nonprofit
organization with six research departments in the U.S.: Embryology, in Baltimore, MD;
the Department of Terrestrial Magnetism and the Geophysical Laboratory in Washington,
DC; The Observatories in Pasadena, CA, and Chile; and Plant Biology and Global
Ecology in Stanford, CA
Amazon drought seen from space
ABC Science Online
Tuesday, 6 April 2004
Satellites using a new technology tested high above the Amazon rainforest can accurately tell scientists about the effects of drought on the ground, according to a new report.
This new application of imaging spectroscopy analysed sunlight reflected from the Earth's surface. Scientists predict that the data it produces may help us understand and predict climate change.
The team, which included researchers from the U.S. and Brazil, published its work on the spaceborne technology online in the Proceedings of the National Academy of Sciences.
Given the size and density of the Amazon, satellites offer the best way of watching what was going on across the giant swathe of forest, the scientists said.
"The Amazon is simply too big and complex to study on the ground alone," said Professor Gregory Asner of the Department of Global Ecology at the Carnegie Institution in Stanford, California, who led the study.
Until now, methods such as the Landsat system of satellites had been used to send back images of the Amazon. But according to the researchers, these were not detailed enough to quantify drought stress on tropical forests and so made it hard for scientists to predict the socioeconomic and ecological effects of drought.
Re-creating drought conditions
Asner and colleagues kept water off a patch of thick Amazon forest for a year to simulate a drought.
They designated a similar patch as a control area, then manually measured rainfall, soil moisture, leaf and canopy characteristics for a year.
They also used NASA's Earth Observing 1 satellite to measure the dryness of the area using imaging spectroscopy.
The researchers found evidence of drought stress, like dry soil and leaves, from the spectroscopy results.
While the reseachers said that the rainforest received an average 2000 millimetres of rain a year, this can vary 600 millimetres a year to 3000 mm another year. And when the weather phenomenon El Niño is active, the area has severe droughts, they said.
But they said it had been impossible to determine what this meant for plant growth, until they tested this new satellite method.
"The fact that we confirmed that satellite imaging can be used to measure something as detailed as the physiology of the rainforest canopy, means that this technique might be useful for understanding other types of ecological phenomena at both large and small scales," Asner said.
"We believe that space-based technology like this is the wave of the future for analysing our planet."
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