Deforestation reduces rainfall in tropics

Large-scale deforestation in tropical rainforests can dramatically reduce rainfall rates both locally and thousands of kilometres away, according to a study published in Nature. This could have a potentially devastating impact on communities living in or close to the Amazon rainforests.

This drop occurs because deforestation reduces the natural recycling of moisture from soils, through vegetation, and into the atmosphere, from where it returns as rainfall.

When forests are replaced by pasture or crops, this water recycling process changes, “leading to reduced atmospheric humidity and potentially suppressing precipitation”, according to researchers from the University of Leeds and the Centre for Ecology and Hydrology, in the United Kingdom.

To measure this activity, researchers combined satellite data on vegetation with data on the direction of prevailing winds. They combined this with satellite data on precipitation to determine whether the air’s increased exposure to vegetation had an effect on rainfall. The model was applied in the Amazon basins, the two largest river basins in the world.

The study showed that “for more than 60 per cent of the tropical land surface, air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation”.

Based on their findings, the authors say the Amazon basin could experience an estimated 12 per cent reduction in wet-season rainfall and a 21 per cent decrease in dry season rainfall by 2050, if Amazon deforestation rates reach the level predicted.

It is even possible that these reductions could extend as far as the Río de la Plata river basin, thousands of kilometres south of the Amazon in southern Brazil, northern Argentina, Paraguay and Uruguay.

Source: Paula Leighton | SciDev.Net