Removing trees has often been thought to increase the amount of water available to hydropower but a new study shows that deforestation reduces the energy output of hydroelectric projects.

The findings have significant implications for large-scale hydropower projects such as Belo Monte being constructed on the Xingu River in Brazil. The country currently generates more than 80 per cent of its energy from hydropower.

The New York Times reports that scientists from the Amazon Institute for Environmental Research together with colleagues from other research institutions have found that the removal of tropical rainforests reduces rainfall. Forests tend to create rain clouds as huge amount of moisture which goes up through their stems, into the leaves and evaporates out into the atmosphere actually feeds rain clouds. Any increase in river flows from removing trees may be outweighed by a decrease in rainfall.

Previously it was believed that river flows increased when trees along streams were removed and no longer took up water from the soil.

The scientists predict that deforestation will reduce the amount of water in rivers to generate hydropower; as much as 40 per cent for the new project in Brazil by 2050.

The findings, which have been published in Proceedings of the National Academy of Sciences of the USA, will also be important for future planning in other tropical rainforest nations which see hydropower as a means of generating ‘green’ power.

Download the full article Dependence of hydropower energy generation on forests in the Amazon Basin at local and regional scales

Read the story in the New York Times: Fewer Rain Forests Mean Less Energy for Developing Nations, Study Finds

See also: Rainbow water: rainfall, the water cycle, forests and trees