An introduction of an essay - 达人(昕昕)

2005/11/08 | An introduction of an essay
类别(冷藏的宝库) | 评论(1) | 阅读(180) | 发表于 16:33: Stripped Amazon gets a lot wetter
30 July 2005
From New Scientist Print Edition. Subscribe and get 4 free issues.

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. "It is a similar effect to the sea breeze, which is caused by the contrast between the land and the sea," says Bras.

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. "Patches that are tens of kilometres wide are perfect for creating the contrast," says Bras.

From issue 2510 of New Scientist magazine, 30 July 2005, page 15; 0