New York Times: Fewer Rain Forests Mean Less Energy for Developing Nations, Study Finds
13 September 2013
The loss of tropical rain forests is likely to reduce the energy output of hydroelectric projects in countries like Brazil that are investing billions of dollars to create power to support economic growth.
For years, scientists and engineers have noted an increase in river flows when the trees along streams are removed. The water in the soil, which would otherwise have been taken up by the tree roots and sent into the atmosphere, instead moves directly into streams and rivers.
At the same time, large areas of tropical forest actually create rain clouds as moisture from their leaves evaporates. So the elimination of swaths of these forests decreases rainfall. Cut down enough trees, the scientists argue, and the indirect impact of lost rainfall outweighs the direct impact of removing trees.
The study, published by The Proceedings of the National Academy of Sciences, predicts that extensive deforestation will leave less water in the rivers to generate hydropower from projects like Belo Monte, which is under construction on the Xingu River in Brazil and will be the world’s third largest hydropower complex.
The Belo Monte project, whose massive scope and impact on the landscape have led to opposition, is expected to generate at least 4,400 megawatts of electricity, the study said. The project’s overall capacity would be more than 11,000 megawatts; because of wide variations in seasonal flows of the Xingu River, the lower output is what developers guarantee.
The idea that deforestation could reduce rainfall and thus economically harm a country like Brazil, which gets more than 80 percent of its energy from hydropower, is less familiar news.
“They removed so much forest that it reduced rainfall and reduced the stream flow,” she added.
A co-author, Daniel C. Nepstad, who like Dr. Stickler works at the Amazon Institute for Environmental Research in Brasília, said rain forests create rain because they “are in the equatorial sun, evaporating a huge amount of water that goes up through the stems and into the leaves and out into the atmosphere.” That moisture feeds rain clouds.
In some eastern and southern tributaries of the Amazon, he added, “the cycle has changed.” The Xingu River, he said, is already near a tipping point where the increased flows caused by the loss of tree roots will be nullified by the overall loss of rainfall.
The authors concluded that “as tropical rain forest nations turn increasingly to hydropower to meet growing demands for ‘green’ electricity, it is important” that planners take into account the links between forest cover and stream flows.