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Marshall Shepherd on how roads and roofs help cause urban floods

EarthSky

Heavy rains we're not the only cause of recent urban flooding, according to University of Georgia research meteorologist Marshall Shepherd. His June 2010 study also blames what he calls ‘impervious cover’ – that is, roofs, streets, and sidewalks – for the disastrous floods in Atlanta in 2009 and Nashville and Oklahoma City in 2010.

近年来美国许多城市洪水肆虐，而强降雨并非其中唯一的成因，佐治亚大学气象学家马歇尔·谢泼德如是说。今年6月通过研究他找出了2009年亚特兰大特大洪灾、2010年纳什维尔、俄克拉荷马城洪水泛滥的其他元凶——不透水的屋顶、马路、人行道等。

Marshall Shepherd: What we found with the Atlanta floods, and indeed many of the recent floods in 2010, is that it was a perfect convergence of several meteorological factors. But one of the other interesting aspects of this flooding event is the real signature of the impervious surfaces of the urban land cover.

马歇尔·谢泼德：我们发现，亚特兰大特大洪灾是多重气象因素完美作用的结果，当然今年这几次洪灾也是如此。但是这场灾害另一个比较有趣的成因是，城区路面、屋顶不透水。

Impervious surfaces, like roofs of buildings, sidewalks and parking lots, don’t absorb the rainwater the way soil does. The water runs off.

屋顶及路面的材质决定了它们不能像土壤那样吸收雨水，于是雨水在地表汇流成河。

Marshall Shepherd: Coupled with um streams and lakes that were already nearing capacity in terms of soil moisture, when you dump a lot of rainfall on urban impervious surfaces, it runs off in volumes quite rapidly. And it really had nowhere to go.

马歇尔·谢泼德：溪流和湖泊已经使土壤含水量接近饱和，要是市区再降暴雨，雨水既无法渗透到地表以下，也无法汇入江河，便在市区迅速汇流，泛滥成灾。因为它们确实无处可去。

Dr. Shepherd said that humans are playing a bigger role than before in creating conditions that are ripe for floods in cities.

谢泼德表示，现在人们无疑在为市区发生洪灾制造更多条件。

Marshall Shepherd: What we're clearly seeing is that the role of human beings and their impervious surface is as much a part of the hydrological water cycle system in cities as the natural environment itself.These are really hand in hand.

马歇尔·谢泼德： 我们清楚地看到人类在其中所起的作用，他们用不透水的材质将城市包裹起来，形成了城市水文与水循环系统的一部分，也参与了自然环境本身的构建。人工环境、水循环系统与自然环境确是一体的。 

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