CAXIUANA NATIONAL FOREST, Brazil — A short walk beneath the dense Amazon canopy, the forest abruptly opens up. Fallen logs are rotting, the trees grow sparser and the temperature rises in places sunlight hits the ground. This is what 24 years of severe drought looks like in the world's largest rainforest.
But this patch of degraded forest, about the size of a soccer field, is a scientific experiment. Launched in 2000 by Brazilian and British scientists, Esecaflor — short for ''Forest Drought Study Project'' in Portuguese— set out to simulate a future in which the changing climate could deplete the Amazon of rainfall. It is the longest-running project of its kind in the world, and has become a source for dozens of academic articles in fields ranging from meteorology to ecology and physiology.
Understanding how drought can affect the Amazon, an area twice the size of India that crosses into several South American nations, has implications far beyond the region. The rainforest stores a massive amount of carbon dioxide, a greenhouse gas that is the main driver of climate change. According to one study, the Amazon stores the equivalent of two years of global carbon emissions, which mainly come from the burning of coal, oil and gasoline. When trees are cut, or wither and die from drought, they release into the atmosphere the carbon they were storing, which accelerates global warming.
Creating drought conditions and observing the results
To mimic stress from drought, the project, located in the Caxiuana National Forest, assembled about 6,000 transparent plastic rectangular panels across one hectare (2.5 acres), diverting around 50% of the rainfall from the forest floor. They were set 1 meter above ground (3.3 ft) on the sides to 4 meters (13.1 ft) above ground in the center. The water was funneled into gutters and channeled through trenches dug around the plot's perimeter.
Next to it, an identical plot was left untouched to serve as a control. In both areas, instruments were attached to trees, placed on the ground and buried to measure soil moisture, air temperature, tree growth, sap flow and root development, among other data. Two metal towers sit above each plot.
In each tower, NASA radars measure how much water is in the plants, which helps researchers understand overall forest stress. The data is sent to the space agency's Jet Propulsion Laboratory in California, where it is processed.
''The forest initially appeared to be resistant to the drought," said Lucy Rowland, an ecology professor at the University of Exeter.