Wet seasons in the Amazon are getting wetter, according to satellite images and observations on the ground. Rainfall increased by at least 180 mm from 1979 to 2015, but what’s driving this long-term trend?
Researchers in China and Brazil found that more than half this change could be due to warming of the tropical Atlantic. Establishing such links is crucial so scientists can better advise on how to safeguard major environmental assets. The Amazon rainforest is a significant sink of carbon dioxide and long-term changes in precipitation could compromise this.
“As rainfall increases during the wet season, photosynthesis is weakened and the growth rate of rainforest plants may slow,” writes the team in Environmental Research Letters (ERL). “These processes affect the energy exchange and the carbon cycle, and beyond that, the precipitation changes could lead to habitat loss and may even result in species extinction.”
The researchers’ atmospheric simulations suggest that variability in sea surface temperatures dramatically increases the convergence of moisture transport over the Amazon region.
The group tested the idea using a single climate model and is keen to clarify the processes taking place in more detail.
“We are currently working on more datasets and models,” says Jiang Zhu from the International Center for Climate and Environmental Sciences (ICCES) in Beijing.
Zhu has followed how oceans have warmed in previous decades. “Because warming oceans will have impacts on land, it is a natural next step to consider important ecological regions such as the Amazon rainforest,” he says.
The rainforest provides around 20% of the Earth’s freshwater discharge and the Amazon basin is an important convective centre, serving as a global source of heat and moisture.
To determine the full picture for Amazon rainfall, Zhu and his colleagues point to a range of mechanisms. Scientists have shown previously that precipitation here is associated with the South American monsoon system. Studies also note the influence of the El Niño Southern Oscillation, which enhances precipitation in east-central South America and decreases equatorial precipitation during the wet season.