Severe droughts in southern Brazil may be linked to deforestation and degradation of Earth's largest rainforest, argues a new report published by a Brazilian scientist.
Reviewing data from roughly 200 studies, Antonio Donato Nobre of Brazil's National Institute for Space Research (INPE) warns that reducing deforestation will not be enough to restore the ecological function of the Amazon rainforest, which acts as a giant water pump that delivers precipitation across much of South America.
Brazilian cities in the southeastern parts of the are currently suffering from a severe drought that has left agricultural areas parched, cut hydroelectric power generation, and drained reservoirs.
In his report, Nobre explains the role big forests like the Amazon play in driving regional weather patterns.
"The forest keeps moist air moving, which brings rain to the interior regions of the continent, thousands of miles distant from the ocean," said Nobre, who is a proponent of the "biotic pump" theory that compares large rainforests to "flying rivers".
"This is due to the innate ability to transfer large volumes of water from the soil to the atmosphere through tree transpiration," Nobre writes, noting that compounds emitted from trees stimulate condensation of water vapor, driving cloud formation and rainfall. This phenomenon reduces atmospheric pressure above forests, pulling moist ocean air deep into interior areas, driving a positive feedback loop that usually ensures regular rainfall in the Amazon and beyond.
However deforestation, degradation, and fire can break the link, disrupting the great moisture pump that delivers moisture to the forest and carries it to other areas, according to Nobre.
"Deforestation can put all of these attributes of the forest at risk. Recognized climate models anticipate varying harmful effects of deforestation on climate, predictions that have been confirmed by observations. Among them are the drastic reduction in transpiration, changes in the dynamics of clouds and rains and prolonged dry season in deforested areas," he states. "Other unanticipated effects, such as smoke and soot damage to the dynamics of rainfall, even in pristine forest areas, are also being observed."
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