Amazon Trees Kick-Start Their Rainy Season

The Amazon’s ecosystem is a fragile balance between the interaction of the plants, animals, microbes and the climate. These depend on each other to keep a flourishing environment. Insects, animals, and microbes depend on the plants for shelter and food, just as the plants depend on them for the breakdown of nutrients which go back into the soil that feeds the trees. Environmental factors are always in play as the dry and wet seasons circle through the year. A new study now links how the plans themselves influence the climate to kick-start the rainy season and keep their ecosystem alive and moving.

Curious climate conditions drove Rong Fu, a scientist from UCLA, to study the unusual start of the Amazon’s rainy season. Normally, moisture from the ocean is carried inland thus starting the rainy season. But in the Amazon, the rainy season starts 2 to 3 months before moist air from the ocean reaches the southern parts of the Amazon.

Previous research showed the accumulation of moisture in the Amazon’s atmosphere but no one was sure why. This new study analyzed water vapor data from NASA’s Tropospheric Emission Spectrometer (TES) on the Aura satellite. Data distinguishes between two isotopes that have different spectral “signatures”, hydrogen and its heavier isotope deuterium. Research shows that water vapor from the ocean does not posses deuterium while the moisture found in the Amazon does.

The study found that during the dry-to-wet seasons, the Amazon forest goes through a greening period where water vapor is released through photosynthesis in a process called transpiration. TES was able to record the water vapor rising from the Amazon rainforest containing deuterium. This gave the definitive proof that water containing deuterium was being absorbed from the ground and released back into the lower atmosphere. This increase of moisture destabilizes the atmosphere starting the rainy season 2-3 months in advance.

These findings opened a window into understanding how this natural mechanism can be affected by deforestation. Reducing the trees will reduce the forest’s ability to produce enough vapor to start the rainy season. Studies predict that if the dry season becomes longer than seven months, the region may transition from a forest to grass plains.

“The fate of the southern Amazon rainforest depends on the length of the dry season, but the length of the dry season also depends on the rainforest,” Fu said.

Resources For Educators:

  1. Take a tour of the Amazon rainforest