An analysis of NASA satellite data revealed Africa's Congo rainforest has significantly declined in greenness over the past decade.
The rainforest is the second largest in the world, a NASA news release reported.
"It's important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate," Liming Zhou of University at Albany, State University of New York, said in the news release.
Greenness is a strong indicator of forest health; the team used satellite-based data on vegetation and measurements called the Enhanced Vegetation Index to make their findings.
The vegetation measurements were taken using the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument.
The researchers found a decreasing trend in the Congo, which was referred to as "browning." Droughts have also killed off a large number of trees in the region.
The browning coincides with the decreasing amount of water believed to be present in the
Congo; the water analysis includes "rainfall, water stored in the ground, water in near-surface soils, or water within the vegetation," the new release reported.
"Combining measurements from different sensors has given us more confidence in the results of the MODIS data and provided us with insights into the environmental and physiological mechanisms of the browning observed by the MODIS data," co-author Sassan Saatchi of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif, said in the news release.
Other factors put even more stress on the plants, such as additional drying sunlight as a result of less cloud cover.
"Forests of the Congo basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years," Saatchi said. "However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests."
"Our assessment is a step toward an improved understanding of how African rainforests respond to increasing drought," Zhou said. "We need to consider the complex range of processes affecting different tropical rainforest species before we can fully assess the future resilience of tropical forests.
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