Tropical deforestation significantly reduces rainfall: study

From the Amazon to the evergreen forests of Africa and Southeast Asia, large-scale deforestation threatens reductions in rainfall across the tropics, according to new research.

The threat is most acute in the Congo Basin -- forecast to endure rapid deforestation in the coming years -- which could see rainfall reduced by up to ten percent by the end of the century, researchers found.

The study, published Wednesday in the journal Nature, used satellite observations over recent decades to confirm predictions in climate change computer models that rainfall would lessen across the tropics as more forest is cut down.

The findings add to concerns that "we could come to a point where the rainforests cannot sustain themselves," said the study's lead author, Callum Smith of the University of Leeds.

He called for increased commitments to conservation, with researchers concluding that restoring large areas of destroyed forest could reverse some of the rainfall loss.

While the importance of tropical forests for the global climate is well known -- they absorb and store planet-warming carbon dioxide -- the impacts of tree loss on local weather conditions have been observed only in specific areas.

The study comes as leaders and experts from around the world gather in Gabon for the One Forest Summit with the aim of protecting forests worldwide.

A major focus at the conference will be the Congo Basin, a crucial carbon "sink" and haven to rare species, second in size only to the Amazon rainforest.

Deforestation -- for cattle pastures, timber exploitation or commodity crops such as palm oil and soybeans -- threatens to worsen climate change and destroy critical biodiversity.

It also risks harming communities.

Despite an expanding agricultural footprint, researchers said crop yields could decline along with forest cover, while increased dryness can increase the frequency of fires, resulting in an overall reduction in productivity in tropical forest regions.

Congo concerns

Using data gathered across the tropical Amazon, Congo and Southeast Asia regions between 2003 and 2017, Smith and his colleagues found that large-scale deforestation disrupts the water cycle and leads to significant rain reduction, with the greatest loss occurring during wet seasons.

Trees return water vapour into the air through their leaves, which can cause localised rainfall.

Previous research focused on small-scale deforestation has suggested that tree loss could actually increase rainfall in some regions.

But at larger scales of tree loss, Smith said, there is "less moisture being pumped back into the atmosphere, then rainfall is reduced."

Of the regions studied, the Congo Basin is forecast to experience some of the "most rapid deforestation" in the coming years, Smith added.

The study's results likely underestimate the full impacts of deforestation on rainfall, he warned, because of an acceleration in tropical forest loss, especially in the Congo.

In the Amazon Basin, the world's largest tropical biome, climate change coupled with forest destruction are pushing the tropical forest towards a "tipping point" where it will shift to a savannah-like state, scientists warn.