The Amazon’s Deforestation Linked to Severe Droughts

which are seeded with volatile gases emitted by the trees naturally, to form rain. These water-rich banks of clouds travel long, wind- driven distances, a conveyor belt for the delivery of precipitation that scientists call flying rivers.

The sky-borne river over the Amazon carries more water than the Amazon River itself. It begins as moisture that builds over the Atlantic Ocean, and then flows westward over the emerald crown of the Amazon, where it picks up far more moisture. The laden clouds eventually bump up against the Andes and are steered south and then east, which means rain for Bolivia and Brazil.

One way forests may move water is known as “biotic pumping.” As water transpires into the atmosphere above the forest, the theory holds, it creates a low-pressure system that sucks in air surrounding it, eventually and continually pumping moisture inland from the ocean. Cutting down forests degrades these low-pressure systems. Large-scale deforestation is thus believed to be a major contributor to Brazil’s extreme drought.

Scientists have long known that vegetation has a profound effect on weather. Researchers are still trying to explain why, but the leading theory is that the darker native plants absorb more heat and release it into the atmosphere, along with energy and water vapor to form clouds.

Today’s researchers rely on computer modeling to understand the effects of deforestation, a difficult task because there are so many complex pathways through which trees control climate: precipitation, carbon storage and absorption of the sun’s energy.

A growing number of scientists are warning that wide- scale deforestation may already be directing precip- itation away from places long accustomed to it. About 20 percent of the Amazon forest is gone already and nearly that much is degraded. One study, from Princeton University in New Jersey, suggested that deforesting the Amazon could contribute to droughts as far away as California.

Antonio Donato Nobre, a veteran climatologist with Brazil’s National Institute for Space Research, recently warned that if just 40 percent of the Amazon region is deforested there could be a large-scale shift to grasslands, which could substantially alter global weather patterns “and cause a breakdown of the current climate system.” If deforestation continues, he has said, São Paulo will most likely “dry up.”

In the broadest sense, scientists say, forests represent a kind of ecological infrastructure that helps maintain comfortable living conditions on the planet, whether by taking up and holding carbon dioxide, cleaning water through their roots or by regulating climate.

Dr. Nobre and other climate experts are urging an immediate halt to deforestation, as well as largescale planting of new forests, as a way to essentially nurse the Amazon back to full health and stabilize its pivotal role in climate.

Some people aren’t waiting for further research and are hoping to geoengineer local climates with new forests. Bishop Fredrick Shoo, of the Evangelical Lutheran Church in Tanzania, has been planting trees with 100,000 of his parishioners upwind of Mount Kilimanjaro for 12 years, in hopes of cooling the hot, dry winds that are melting the mountain’s glaciers. He estimates they have planted 3.7 million trees.

“We have a moral obligation to take care of creation and to be sure coming generations have a good place to live,” he said.