Deforestation drives decreases in rainfall across the tropics

Photo: Pixabay/Quangpraha

Less rainfall and fewer forests across the tropics are increasingly a fact of life for millions of people in the torrid region, yet the two environmental hazards are more closely linked than widely assumed.

The loss of tree cover in the tropics is likely leading to reductions in rainfall, according to experts at the University of Leeds, who reached this conclusion by combining satellite data of deforestation and rainfall in three areas of the tropics: the Amazon, Congo and Southeast Asia from 2003 to 2017.

Their aim was to see if the rate of rainfall in areas where forests had been cleared was different from the rate of rainfall in nearby locations where no forests had been lost.

If uncontrolled deforestation in the Congo continues unabated, they have found, rainfall in the region could be reduced by between 8% and 12% by the end of the century. This would severely impact biodiversity and farming alike while also posing a grave threat to the forests in the Congo, which constitute some of the world’s largest stores of carbon.

“Tropical forests play a critical role in the hydrological cycle through helping to maintain local and regional rainfall patterns. The reduction in rainfall caused by tropical deforestation will impact people living nearby through increased water scarcity and depressed crop yields,” explains Callum Smith, a doctoral researcher at the university’s School of Earth and Environment.

“Tropical forests themselves rely on moisture to survive and remaining areas of forest will be impacted by a drier climate,” notes Smith, who was the lead author of a study on the findings.

Tropical forest loss caused reductions in rainfall throughout the year, even in the dry season “when any further drying will have the biggest ramifications on plant and animal ecosystems,” the scientists say.

“The greatest absolute decline in precipitation was seen in the wet season with up to a 0.6mm a month reduction in rainfall for every percentage point loss of forest cover,” they add.

The likely reason for a loss in rainfall in deforested areas is that the loss of tree cover disrupts the process of moisture from leaves is returned to the atmosphere, through a mechanism called evapotranspiration, where it eventually forms rain clouds.

This can have severe consequences for people living in these areas as well as for biodiversity.

“Local people living near deforested regions often report a hotter and drier climate after the forests are cleared. But until now this effect had not been seen in rainfall observations,” says Prof. Dominick Spracklen, of the School of Earth and Environment at Leeds University.

“The study shows the critical importance of tropical forests in sustaining rainfall. Although there have been efforts to halt deforestation, the loss of forest cover in the tropics has continued. There needs to be renewed efforts to stop forests being lost and to regenerate lost and degraded areas.”