Trees in the Amazon Generate Their Own Clouds and Rain, Study Finds

Scientists have discovered that trees in the Amazon release enough moisture through photosynthesis to create low-level clouds and generate rain, according to a new study published in the Proceedings of the National Academy of Sciences.

The research answers a long-debated question about why Amazonian rains start months before seasonal winds bring in moist air from the ocean, reported Science magazine.  

Researchers used water vapor data collected by NASA’s Aura satellite to study the composition of moisture over the Amazon. They found that at the end of the dry season, when plants are growing at their fastest rates, atmospheric moisture was high in deuterium, a heavy isotope of hydrogen that is present in water vapor from photosynthesis, but absent in water evaporated from the ocean. The work was led by Rong Fu, a climate scientist at the University of California, Los Angeles.

The tree-generated moisture is heavy enough to create low-level clouds and produce light rain. It might even be strong enough to shift wind patterns and bring in moisture from the ocean, triggering the start of the heavier rain season, the researchers theorized. Fu and his colleagues are now studying whether the same process takes place in rainforests in the Congo.