Human Activities Are Drying Out the Amazon
A recent NASA study shows that over the last 20 years, the atmosphere above the Amazon rainforest has been drying out due to the human activities– increasing the demand for water and leaving ecosystems vulnerable to fires & drought.
NASA’s Jet Propulsion Laboratory scientists in Pasadena, California, analyzed decades of ground & satellite data over the Amazon rainforest to track how much moisture was actually in the atmosphere and how much moisture was needed to maintain its rainforest system.
JPL’s Armineh Barkhordarian, the lead author of the study, said they observed that in the past 2 decades years, there has been a significant increase in dryness in the atmosphere and in the atmospheric demand for water above the rain-forest. He further explained when comparing this trend to data from models that estimate climate variability over thousands of years; the team determined that the change in atmospheric aridity is well beyond what would be expected from natural climate variability.
So if it is not natural, what is causing it?
He said that elevated greenhouse gas levels are responsible for approximately half of the increased aridity. The rest is because of ongoing human activity, most significantly, the burning of forests to clear land for agriculture and grazing. The combination of these activities is causing Amazon’s climate to warm.
And when a forest burns, it releases particles called aerosols into the atmosphere and among them, black carbon, commonly referred to as soot. While bright-colored or translucent aerosols reflect radiation, the darker aerosols absorb it. And when the black carbon absorbs heat from the sun, it causes the atmosphere to warm. This can also interfere with cloud formation and, consequently, even the rainfall.
Amazon is the largest rainforest on Earth. When healthy, amazon absorbs billions of tons of carbon dioxide a year through photosynthesis. By removing carbon dioxide from the atmosphere, the Amazon helps to keep temperatures down & also regulates climate.
But it is a delicate system that is highly sensitive to drying and warming trends.
Trees & plants need water for photosynthesis and to cool themselves down when they get too warm. Trees pull in water from the soil through their roots and then release water vapor through their pores on the leaves into the atmosphere, where it cools down the air & eventually rises to form the clouds. Clouds produce rain that replenishes the water in the soil that in turn allows the cycle to continue. The rainforests generate as much as about 80 percent of their own rain, especially during the dry season.
But when this cycle is disrupted by an increase in dry air, for instance, a new cycle is set into motion –one with significant implications, particularly in the southeastern Amazon, where trees can experience more than 4 to 5 months of the dry season.
It is a matter of supply & demand. With the increase in temperature and drying of the air above the trees, they need to transpire to cool themselves and to add more water vapor into the atmosphere. But the soil does not have extra water for the trees to pull in, said JPL’s Sassan Saatchi, co-author of the recent study. He added the study shows that the demand is increasing, the supply is decreasing and if this continues, the forest may no longer be able to sustain itself.
Researchers observed that the most significant and systematic drying of the atmosphere is in the southeast region, where the bulk of deforestation & agricultural expansion is happening. But they also found episodic drying in the northwest Amazon which is an area that typically has no dry season. The northwest has suffered severe droughts over the past 2 decades, a further indication of the entire forest’s vulnerability to increasing temperatures & dry air.
And if this trend continues over the long term and rainforests might reach the point where it can no longer function properly and many of the trees & the species that live within them and its ecosystem may not be able to survive. As the trees die, particularly the larger & older ones, they release carbon dioxide into the atmosphere and the fewer trees there are, the less carbon dioxide the Amazon region would be able to absorb — meaning we would essentially lose an important element of climate regulation.
The recent study, “A Recent Systematic Increase in Vapor Pressure Deficit Over Tropical South America,” was published in October in Scientific Reports. The research team used data from NASA’s Atmospheric Infrared Sounder (AIRS) instrument aboard the Terra satellite.