Scientists show a clear link between deforestation and a local drop in rainfall.
Deforestation and regional precipitation are now clearly linked for the first time, according to researchers. Scientists hope it will inspire governments and agricultural businesses in the Amazon, Congo, and south-east Asia to put more money into protecting trees and other vegetation.
According to the study, local farmers in tropical countries will be less able to rely on rain for their crops and pastures the more rainforests are cleared.
The paper, which was published in Nature, adds to the concern that the Amazon is rapidly deteriorating to the point where the rainforest will no longer be able to produce its own rainfall and the vegetation will dry up.
Anecdotal evidence of drier microclimates has long been provided by individuals living in deforested areas. Since removing trees reduces evapotranspiration, it was assumed that this would lead to less rainfall in the area.
Using satellite and meteorological data from 2003 to 2017, the Leeds University team has now demonstrated this across pantropical regions.
They discovered an effect even at a small scale, but the decline became more pronounced when the affected area was larger than 50 kilometers square (2,500 kilometers square). The study found that for every one percentage point of forest loss, monthly rainfall was 0.25 percentage points lower at the largest measured scale of 200 km squared (40,000 km2).
This can become a vicious cycle because less rain means more forest loss, more vulnerable to fire, and less carbon drawdown.
According to Prof. Dominick Spracklen of the University of Leeds, one of the authors, between 25% and 50% of the rain that fell in the Amazon was recycled by the trees. Although the forest is sometimes referred to as the “lungs of the world,” in reality, it more closely resembles a heart that circulates water throughout the area.
He stated that arguments regarding carbon sequestration, which were viewed as having more advantages for industrial nations in the northern hemisphere, were more persuasive to governments and businesses in the global south than the local impact of this reduced water recycling.
“Demonstrating the local benefit of keeping tropical forests standing for the people living nearby has important policy implications,” Spracklen said. “I hope our work will provide a strong incentive for policy and decision makers within tropical nations to conserve tropical forests to help maintain a cooler and wetter local climate, with benefits for nearby agriculture and people.”
The authors also looked ahead at what might happen if more trees were cut down. Based on projections of forest loss, they estimated that rainfall in the Congo Basin would fall by 16 millimetres per month by the end of the century.
The effects will likely be felt in cities and farmlands hundreds or thousands of kilometres away from the cleared forest in every region. Crop yields could decrease by 1.25 percent for every 10 percentage point reduction in forest cover, according to the study.
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