VOA慢速英语 2008 1020a

This is the VOA Special English Development Report.

Green roofs are designed to save energy and capture rainwater. Rooftops covered with plants help keep buildings cool. They can extend the life of a roof. And they can reduce water runoff into streets and storm water systems.
　

Chicago City Hall

Several years ago, the mayor of Chicago, Illinois, visited Germany, a leader in green roof design. Mayor Richard Daley later decided¹ to have vegetation planted on Chicago City Hall. Today, the tops of many other buildings also look like parks.

In Canada, the Coast Plaza² Hotel in Vancouver has a forest on its roof.

Experts say green roofs usually do not get much above twenty-seven degrees Celsius³. So temperatures might not be a problem for growing. But rooftop gardeners have to be careful not to put too much weight on the roof. This is true whether plants are grown in soil or water.

New York City has an unusual demonstration⁴ farm for hydroponics. The farm is on a boat called the Science Barge⁵. Rainwater and purified river water are used to grow lettuce⁶, tomatoes, cucumbers and peppers. The farm shows the possibilities for designing rooftop systems.

Earlier this year, researchers in Texas reported that green roofs can reduce a building's air conditioning costs by about one-fifth compared to black-top roofs. But they also reported that not all green roofs perform equally well. They found that designs differ in their ability to keep buildings cool and to capture rainwater.

Mark Simmons led the study for the Lady Bird Johnson Wildflower Center at the University of Texas at Austin. "Green roofs have to be done right," he says. For example, he says, "Just having a green roof may not mean anything in terms of preventing water from reaching the street level."

The team put experimental roofs on top of metal insulated boxes, to recreate green roof conditions. The study compared products from six companies. The researchers say they want to help businesses understand how to improve their designs.

Each rooftop had sixteen different kinds of plants native to Texas. The researchers say the presence of native plants likely helped all the green roofs capture water better compared to sedums. Sedums are plants that need little water and often are used on green roofs.

The native plants could take in more water and release more of it to the atmosphere.

And that's the VOA Special English Development Report, written by Jerilyn Watson.

1 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

2 plaza   

n.广场，市场

参考例句：

• They designated the new shopping centre York Plaza.他们给这个新购物中心定名为约克购物中心。
• The plaza is teeming with undercover policemen.这个广场上布满了便衣警察。

3 Celsius   

adj.摄氏温度计的，摄氏的

参考例句：

• The temperature tonight will fall to seven degrees Celsius.今晚气温将下降到七摄氏度。
• The maximum temperature in July may be 36 degrees Celsius.七月份最高温度可能达到36摄氏度。

4 demonstration   

n.表明，示范，论证，示威

参考例句：

• His new book is a demonstration of his patriotism.他写的新书是他的爱国精神的证明。
• He gave a demonstration of the new technique then and there.他当场表演了这种新的操作方法。

5 barge   

n.平底载货船，驳船

参考例句：

• The barge was loaded up with coal.那艘驳船装上了煤。
• Carrying goods by train costs nearly three times more than carrying them by barge.通过铁路运货的成本比驳船运货成本高出近3倍。

6 lettuce   

n.莴苣；生菜

参考例句：

• Get some lettuce and tomatoes so I can make a salad.买些莴苣和西红柿，我好做色拉。
• The lettuce is crisp and cold.莴苣松脆爽口。