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Drought-Stressed Forest Fueled Amazon Fires A new satellite-based
map of a section of the Amazon Basin reveals that at least some of the massive
fires burning there this past summer were concentrated in water-stressed areas
of the rainforest. The stressed plants released measurably less water vapor
into the air than unstressed plants; in other words, they were struggling to
stay cool and conserve water, leaving them more vulnerable to the fires.
The fires in
the Amazon Basin, which continue to burn into November, are mainly the result
of such human activities as land clearing and deforestation. The pattern - spotted
from space by NASA's ECOsystem Spaceborne Thermal Radiometer Experiment on
Space Station (ECOSTRESS) - points to how water-stressed plants can impact the
spread of fires. The data may one day help NASA's Earth-observing missions predict
the path of future forest or brush fires like those currently raging in
California.
The primary
mission of ECOSTRESS, an instrument that measures thermal infrared energy
emitted from the land surface, is to provide insight into plants' health by
taking their temperature. To keep cool, plants "sweat" by releasing
water vapor through their pores, a process called evapotranspiration. After
multiple orbits, ECOSTRESS is able to measure how much plants transpire and
track their response to climate change.
In August,
fires spread over large swaths of the Amazon Basin. ECOSTRESS captured the
first image of the Amazon rainforest in Peru before the fires began, on Aug. 7.
It shows a surface temperature map revealing water-stressed and non-stressed
forest (shown in brown and blue, respectively). The fire icons
represent fires imaged by NASA's Terra satellite between Aug. 19 and 26. The fires are limited primarily to areas
of water-stressed plants that transpired the least. The second image, taken by the Terra
satellite on Aug. 18, shows the ECOSTRESS study area and smoke from active
fires in the rainforest.
The image also
reveals how certain parts of the forest were more resilient, seeming to protect
themselves from burning. Plants in these areas were cooler - in other words,
they released more water vapor from their leaves - than plants in the burn
zones, though mission scientists don't know whether that's a coincidence or a
direct causal relationship. The water-stressed areas of the forest look as
green and healthy as these cooler areas, making them invisible except to a
radiometer that can measure thermal infrared energy from the surface.
"To the
naked eye, the fires appear randomly distributed throughout the forest,"
said Josh Fisher, ECOSTRESS science lead at NASA's Jet Propulsion Laboratory in
Pasadena, California. "But, if you overlay the ECOSTRESS data, you can see
that the fires are mainly confined within the highly water-stressed areas. The
fires avoided the low-stress areas where the forest appears to have access to more
water."
It's still a
mystery why some plants become stressed while other plants don't, though
scientists believe it's dependent on factors like the species of plant or
amount of water in the soil. The data from ECOSTRESS will help answer questions
about which plants will thrive in their changing environments and could also be
used to help with decisions related to water management and agricultural
irrigation.
JPL built and
manages the ECOSTRESS mission for the Earth Science Division in the Science
Mission Directorate at NASA Headquarters in Washington. ECOSTRESS is an Earth
Venture Instrument mission; this program is managed by NASA's Earth System
Science Pathfinder program at NASA's Langley Research Center in Hampton,
Virginia.
More
information about ECOSTRESS is available here:
https://ecostress.jpl.nasa.gov
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