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article imageThe Amazon's 'weather engine' has impacts on rainfall globally

By Karen Graham     Aug 27, 2019 in Science
The Amazon's lush greenery and network of waterways are at risk in the face of this summer's record fires, but another force of nature brewing high above the landscape is also deserving of attention, scientists and researchers say.
The unusually large increase in the number of fires in Brazil's Amazon rainforest this year have more than likely been set on purpose by farmers, logging and mining companies. But the damage being done is staggering and will have long-term consequences for humanity.
That being said, Brazil’s government has launched a firefighting initiative, deploying troops and military planes to put out the fires, but this effort will only extinguish smaller blazes and help prevent new fires, experts are saying, reports Reuters.
Precipitation in the Amazon
The annual rainy season won't begin until around September 15, but this presents another problem. Rainforests are subject to heavy rainfall, at least 80 inches (2,000 millimeters) — and in some areas over 430 inches (10,920 mm) — of rain each year. And herein lies the problem - and it could turn out to be very serious.
Brazil includes about 60 percent of the Amazon rainforest  the largest in the world and essential in...
Brazil includes about 60 percent of the Amazon rainforest, the largest in the world and essential in the exchange of CO2 for oxygen
Studies by researchers at NASA's Jet Propulsion Laboratory on the average rainfall in the Amazon show that rainfall has been declining since about 2003, while dry spells or droughts have gotten worse. This seems to indicate that the rainforest is showing the first signs of large-scale degradation due to climate change.
"Our results suggest that if droughts continue at five- to 10-year intervals or increase in frequency due to climate change, large areas of the Amazon forest are likely to be exposed to persistent effects of droughts and corresponding slow forest recovery," said NASA scientist Sassan Saatchi, lead researcher of the study. "This may alter the structure and function of Amazonian rainforest ecosystems."
Maria Silva Dias is a professor of atmospheric sciences at the University of Sao Paulo. She told Reuters that less precipitation is expected in parts of the Amazon experiencing the worst fires, while in the eastern parts of the forest, it is expected to be very dry.
The clouds in this image of the Amazon Rainforest are a result of evapotranspiration. Image dated: A...
The clouds in this image of the Amazon Rainforest are a result of evapotranspiration. Image dated: August 25, 2009.
NASA image courtesy Jeff Schmaltz, MODIS Rapid Response at NASA GSFC.
“In some points, you could put out some fires, certainly, but these are isolated points, it’s not the whole area,” Dias said. “The whole area needs it to rain more regularly, and this will only happen further down the line, around October.”
Matias Sales a meteorologist for Brazil weather information firm Climatempo notes that the 15-day rain forecast is at or below the average for this period in previous years, and generally, this will not put out the fires.
Why do fires in the Amazon affect weather in the US?
Scientists and environmentalists talk about the Amazon being the lungs of the Earth, and they are correct. Actually, all the rainforests around the globe make up this Earthly organ.
Luiz E.O.C. Aragao,
You could say the Amazon is also a living organism with a special purpose. likens the towering mahogany, kapok, and Brazil nut trees of the Amazon as an important part of the orchestra of the region’s water system, eventually affecting weather systems.
The trees take in water through their root systems, nourishing the tree and moving it up into the canopy where it is released into the air in a process called evapotranspiration. Transpiration rates vary widely depending on weather conditions, such as temperature, humidity, sunlight availability and intensity, precipitation, soil type and saturation, wind, and land slope.
But with the trees, plants, and shrubs in the Amazon disappearing at an alarming rate, this orchestra will fall out of tune. The outcome is disastrous. The forest will die - with a wave of death that will turn the dense forest into a sparsely filled Savannah. This is known as "forest dieback."
A 2014 study in the journal Nature Climate Change looked at "forest dieback" and found that "complete Amazon deforestation would reduce rainfall in the U.S. Midwest, Northwest and parts of the south during the agricultural season."
The Amazon weather machine
This scenario is possible because the Amazon is also a "weather machine." Everyone has now heard of "atmospheric rivers." Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky - that transport water vapor from the Tropics.
These columns of water vapor move with the weather. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow., according to NOAA. Some of these atmospheric rivers that carry the largest amounts of water vapor and the strongest winds can create extreme rainfall and floods, like the "Pineapple Express" that hit California in 2010.
However, the continued loss of vegetation in the Amazon could have a cumulative effect, not only in contributing to climate change but also affecting rainfall patterns around the globe, including the U.S. Midwest.
Meg Symington, the World Wildlife Fund's senior director for the Amazon in the United States said, "It's well-known that the weather patterns affect rainfall in the breadbasket of South America," she added, "but there's also evidence that it affects the breadbasket that is the middle of the U.S."
"We worry that we will soon cross a threshold of forest loss, a point of no return, after which the water recycling pump will be insufficient to maintain the system and we will see forest collapse independent of further human depredations," said Scott Saleska, a University of Arizona professor who has been studying the Amazon for 20 years, in an email to NBC News.
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