Understanding Change in the Biosphere
Produced in collaboration with D. Nepstad and E. Davidson (Woods Hole Research Center), with grant support from the National Science Foundation
Support for computing resources provided by the High Performance Computing and Communications (HPPC) Program by granting access to their testbed computers at the Numerical Aerodynamic Simulation (NAS) facility at NASA-Ames.
In addition to routinely using satellite images to map areas of deforestation in the Amazon, these large digital files have been transferred directly into a complex computer simulation model of the rain forest ecosystem. The satellite continuously feeds in data on the state of the forest cover throughout the year. This NASA computer model is then used to estimate how the cycling of water and nutrients is changing throughout the entire area of Brazil.
By using images from space it is possible to detect effects of deforestation on both the land cover and the productivity of the entire Amazon region. The NASA computer model takes this approach a step further to estimate the region-wide emission rates of so-called "greenhouse" gas emissions, like carbon dioxide and nitrous oxide, which are gases that are known to contribute directly to global warming.
FIGURE CAPTION: Brazil NPP
Net primary production estimated at 8-km cell resolution by the NASA-CASA model for Brazil, circa 1990.
To view a monthly animation of Net primary production download 4.2Mb mpeg amazon.mpeg
It is estimated from this NASA computer model that Amazon rain forests are one of the largest natural sources of greenhouse gases. Natural gas emissions from the rain forests help maintain a normal balance of heat in the atmosphere. When Amazon forests are cut and converted to cattle ranches, the new pasture systems become sources of different types of reactive gases in the atmosphere that are not necessarily in balance with the natural environment of the rain forest.
This NASA computer model also suggests that pastures and annual crops planted in areas of cleared Amazon rain forests fix less carbon each year, and are less tolerant of drought, than are the forest tree species that they replace. This is partly because the rooting systems of pastures and crops appear to be less efficient at tapping deep soil moisture pools, compared to the extensive deep roots of the native rainforest trees.
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