Tropic Rainmakers

Drier days could be ahead for areas downwind of rainforest deforestation. New research shows that lush canopies return moisture to the atmosphere, seeding rain hundreds of kilometers away. Air originating from dense rainforest produces twice as much rain as air traveling from cleared areas. The findings, reported in Nature, suggest rainforest loss could have lasting impacts on climate throughout the region.

The rainforest is known to return much of its water back into the atmosphere through evaporation and transpiration. But scientists lacked evidence connecting this rainwater reuse to precipitation throughout the tropics, though some previous studies suggested that cleared areas received more rainfall than neighboring forests.

To determine the role of rainforest recycling and the impact of dense vegetation, the research team used satellite data to track moisture levels and precipitation as air masses traveled across the tropics.

They found that impacts could be seen hundreds of kilometers away, suggesting that deforestation in one country could affect distant communities across borders. Those regions could face a double blow with diminishing rains due to both deforestation and climate change. If projections hold for deforestation in the Amazon, the authors calculated that the region could see about a fifth less rainfall during the 2050 dry season.

“Such a reduction in precipitation may have consequences for the future of remaining Amazonian forests and for rainfall-reliant industries both within and outside the Amazon basin, including agriculture and hydroelectric power generation,” the authors write. “The successful efforts to curb Amazon deforestation that have been applied in recent years must be maintained if large-scale clearance of the Amazon and the resulting impacts on regional rainfall are to be avoided.”Caitlin Stier | 6 September 2012

Source: Spracklen, D. V. et al. 2012. Observations of increased tropical rainfall preceded by air passage over forests. Nature doi: 10.1038/nature11390

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