For the first time, the researchers showed a clear correlation between deforestation and local rainfall. Scientists hope this could encourage agricultural companies and governments in the Amazon and Congo Basin regions and Southeast Asia to invest more in protecting trees and other vegetation.
The study adds to fears that the Amazon is reaching a tipping point after which it will be unable to generate its own rain.
Scientists have found that the more rainforests are cleared in tropical countries, the less local farmers can rely on rain for their crops and pastures.
The article, published in the journal Nature adds to fears that Amazon degradation is reaching a tipping point, after which the rainforest will no longer be able to generate its own rain and vegetation will dry up.
People living in deforested areas have long provided anecdotal evidence that their microclimates have become drier with less tree cover. Scientists already knew that killing trees reduces evapotranspiration, and therefore theorized that this would result in less local precipitation.
The relationship between deforestation and local rainfall
The University of Leeds team demonstrated this using meteorological and satellite records from 2003 to 2017 in pantropical regions.
Even on a small scale, they found an impact, but the decline became more pronounced once the affected area surpassed 50 square kilometers (2,500 square kilometers). At the largest measured scale of 200 square kilometers (40,000 square kilometers), the study found that rainfall was 0.25 percentage points less each month for each percentage point of forest loss.
This can enter a vicious cycle, as reduced rainfall leads to increased forest loss, increased vulnerability to fire and reduced carbon sequestration.
Trees and water recycling
One of the authors, Professor Dominick Spracklen of the University of Leeds, said that between 25% and 50% of the rain that fell in the Amazon came from the recycling of rain from trees. Although the forest is sometimes described as the “lungs of the world”, it functions much more like a heart that pumps water throughout the region.
He said the local impact of this reduction in water recycling was much more obvious, immediate and persuasive to governments and corporations in the global south than arguments about carbon sequestration, seen as having more benefits for industrialized countries in the northern hemisphere.
“Demonstrating the local benefit of keeping rainforests standing for people who live nearby has important policy implications.Spracklen said. “I hope that our work will provide a strong incentive for policy and decision makers in tropical nations to conserve rainforests to help maintain a cooler, wetter local climate, with benefits for agriculture and people nearby.”.
The authors also expected the possible effects of more deforestation. For the Congo Basin, they estimated a reduction in precipitation of 16 mm per month by the end of the century, based on projections of forest loss.
In all regions, the fallout is likely to be felt in cities and farmland hundreds or thousands of kilometers from the cleared forest. The study indicates that crop yields can decrease by 1.25% for every 10 percentage points of forest cover loss.