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Dam It’s impossible to write about how human activities are altering the climate, that trivial humanity cannot possibly alte

admin2013-05-04  81
问题                                 Dam
    It’s impossible to write about how human activities are altering the climate, that trivial humanity cannot possibly alter such a giant system through loading the atmosphere with an additional 0.000115 percentage points of carbon dioxide.
    Unfortunately for the denialists, examples of how human activities can alter climate keep accumulating. The latest has nothing to do with the greenhouse effect but underlines the fact that ordinary activities can have unexpected meteorological consequences. So we infer large dams seem to be altering rainfall patterns. It is becoming clearer that in addition to providing lots of water to evaporate and then return to the ground as rainfall, dams also make local meteorological conditions more helpful to rainfall.
    In particular, explain Faisal Hossain of Tennessee Technological University, dams increase atmospheric instabilities in the vertical profile of temperature and humidity. Those instabilities arise because the presence of a dam increases evaporation and there-fore atmospheric moisture. That enhances the amount of corrective energy in the air above the reservoir. The end result: more rainfall.
    Weather records support this theoretical reasoning. For one thing, there are more thunderstorms in the vicinity of a large dam compared with before the dam was built. For another, large dams are contributing to the "when it rains, it pours" phenomenon: longer periods without rainfall punctuated by drenching, flood-inducing downpours.
    The significance of dams altering local weather is not merely another example of the power of human activities to change the climate. There is also a more practical issue. When dams are constructed, engineers make assumptions about how frequently large floods will occur, and they build the dam to withstand them. But if the uncommon flood occurs more frequently because of the very presence of a dam, that calculation is wrong, and the dam may be subjected to more frequent and more extreme flood-inducing downpours.
    As one researcher warns, it is therefore possible that a large dam may be found years later to actually have been designed for a flood with a much lower recurrence interval (or higher frequency) than originally expected because the frequency of extreme precipitation events has increased due to the reservoir’s presence. Such a possibility raises concerns about dam safety. That risk is compounded by the fact that conventional dam and reservoir design over the past century has been ’ one-way’, with no acknow-ledgment of the possible feedback mechanisms between the presence of a dam and rainfall. "Indeed, dam design protocol in civil engineering continues to assume unchanging patterns of extreme rainfall events." The risk is also compounded by the age of dams: some 85 percent of large dams in the United States will be more than 5 0 years old by 2020.
    If only the idea that "no one does anything about the weather" were true.
Which of following is TRUE about the relationship between dams and rainfall?
选项 A、Atmospheric stabilities increase the evaporation.
B、There were fewer thunderstorms before the dam was built.
C、Rainfall leads to more amount of convective energy in the air.
D、Large dams lead to a long period without rainfall at all.
答案B
解析 推理判断题。本题考查水坝和降水之间的关系。文章在第二、三和四段对此话题进行了着重的论述。由第四段第二句:…there are more thunderstorms in the vicinity of a large dam compared with before the dam was built．可知，和建起大坝以前相比，建起大坝以后大坝附近出现了更多的雷雨天气。就是说大坝建起之前比建起之后的降雨少，故选[B]项。[A]项“气流的稳定增加了水分的蒸发”，[C]项“降雨导致了更多的空气对流”和[D]项“大坝导致了长期的滴雨不下”均不正确。
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