DEFORESTATION in the Amazon rainforest is creating more rainfall in the areas stripped of trees.
Frederic Chagnon and Rafael Bras of the Massachusetts Institute of Technology compared 75 years of rain-gauge records with satellite data of cloud and forest cover over Brazil. They found that about twice as many low-level clouds formed over deforested areas as over forest, leading to more rainfall in such places.
The extra clouds form because of contrasts between forested and deforested areas in, for instance, the rate at which water evaporates from them and the roughness of their surfaces. 鈥淚t is a similar effect to the sea breeze, which is caused by the contrast between the land and the sea,鈥� says Bras.
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Currently, about 15 to 20 per cent of the Amazon region has been deforested, but further logging will not necessarily lead to more rainfall. If the deforested areas are too small or too large, they do not provide the contrast needed to produce the localised convection patterns that brew the clouds. 鈥淧atches that are tens of kilometres wide are perfect for creating the contrast,鈥� says Bras.
