05 Aug Trees in the Amazon make their own rain

The Amazon rainforest is home to strange weather. One peculiarity is that rains begin 2 to 3 months before seasonal winds start to bring in moist air from the ocean. Now, researchers say they have finally figured out where this early moisture comes from: the trees themselves.

The study provides concrete data for something scientists had theorized for a long time, says Michael Keller, a forest ecologist and research scientist for the U.S. Forest Service based in Pasadena, California, who was not involved with the work. The evidence the team provides, he says, is “the smoking gun.”

Previous research showed early accumulation of moisture in the atmosphere over the Amazon, but scientists weren’t sure why. “All you can see is the water vapor, but you don’t know where it comes from,” says Rong Fu, a climate scientist at the University of California, Los Angeles. Satellite data showed that the increase coincided with a “greening” of the rainforest, or an increase in fresh leaves, leading researchers to suspect the moisture might be water vapor released during photosynthesis. In a process called transpiration, plants release water vapor from small pores on the underside of their leaves…

https://www.sciencemag.org/news/2017/08/trees-amazon-make-their-own-rain