According to a newly published study, NASA satellites have revealed that Amazon forests are neither evergreen nor dependent on constant rain, and are capable of manufacturing their seasons.

A team of 27 researchers from 15 institutions used satellite images to study the amount and dynamics of green leaf area of Amazon rainforests. The study was made possible by more than five years of daily estimates of leaf area over the entire Amazon basin using the Moderate Resolution Imaging Spectroradiometer’s 1-meter resolution imagery aboard the NASA Terra satellite.

The researchers reported that the rainforests sprout new leaves in anticipation of the coming dry season. The greener forests capture more sunlight, absorb more carbon dioxide and evaporate more water during the dry season compared to the wet season. By gradually humidifying the atmosphere, the forests play an integral role in the onset of the wet season. In fact, the rainforests sprout new leaves in anticipation of the coming dry season.

The study notes a 25 percent increase in the amount of green leaf area in the season when skies are relatively clear. It found that the rainforests are more dependent on light than rain, enduring several months of dry season by tapping water deep in the soil with their long roots.

Such results of the NASA-funded project were published in the March 20 issue of the Proceedings of the National Academy of Sciences.

"Our finding is similar to the discovery of a large green continent, nearly a third the size of South America, appearing and disappearing each year," explained Ranga Myneni, professor of geography and environment at Boston University, the study’s lead author. "This has very important consequences for weather, atmospheric carbon, water and nutrient cycling, given that leaves are the air purifiers and food factories of our planet."

The Amazon rainforest covers an area equivalent to more than half of the continental United States, and is home to more than one-third of all living species on Earth.

Scientists used satellite images to study the amount and dynamics of green leaf area of Amazon rainforests.

"This work is an important outcome of over 10 years of NASA’s investments and teamwork to develop, build and launch state-of-the art sensors and processing algorithms enabling the discovery of hitherto unknown vegetation dynamics on Earth," added Rama Nemani, a co-author of the paper at NASA Ames Research Center in Moffett Field, Calif.

The work was made possible through funding by NASA as part of a long-term research program dedicated to understanding how human-induced and natural changes affect the global environment.