Climatic changes such as changes in temperature,precipitation,humidity, or wind speed that are produced byurbanizationinvolve all major surface conditions. Some of these changes are quite obvious andrelativelyeasy to measure. Others are moresubtleand sometimes difficult to measure. Theamountof change in any of these elements, at any time, depends on several variables, including theextentof theurbancomplex, the nature of industry, site factors such astopographyandproximityto water bodies, time of day, and existing weather conditions.

The most studied and well-documentedurbanclimaticeffect is theurbanheat island. Thetermsimplyrefers to the fact that temperatureswithincities are generally higher than in rural areas. The heat island isevidentwhen temperature data are examined. For example, thedistributionof averageminimumtemperatures in the Washington, D.C.,metropolitanarea for the three-month winter period (DecemberthroughFebruary) over a five-yearspan, clearly represents a well-developed heat island. The warmest winter temperatures occurred in the heart of the city, while the suburbs and surrounding countryside experienced averageminimumtemperatures that were as much as 3.3°Clower. Remember that these temperatures are averages, because on many clear, calm nights the temperature difference between the city center and the countryside wasconsiderablygreater, often 11°C or more. Conversely, on many overcast or windy nights the temperature differential approached zero degrees.

Theradicalchange in the surface that results when rural areas are transformed into cities is asignificantcause of theurbanheat island. First, the tall buildings and theconcreteand asphalt of the cityabsorband store greater quantities ofsolarradiationthan do thevegetationand soiltypicalof rural areas. In addition, because the city surface isimpermeable, therunoffof water following a rain is rapid, resulting in aseverereductionin theevaporationrate. Hence, heat that once would have been used toconvertliquidwater to a gas now goes to increase the surface temperature. At night, while both the city and the countryside cool by radiative losses, the stone-like surface of the city gradually releases theadditionalheat accumulated during the day, keeping theurbanair warmer than that of theoutlyingareas.

Aportionof theurbantemperature rise must also be attributed towasteheat from sources such as home heating and air conditioning, power generation, industry, andtransportation. Many studies have shown that themagnitudeof human-generated energy inmetropolitanareas is great when compared to theamountof energy received from the Sun at the surface. For example, investigations in Sheffield, England, and Berlin, Germany, showed that theannualheat production in those cities was equal toapproximatelyone-third of that received fromsolarradiation. Another study of densely built-up Manhattan in New York City revealed that during the winter, thequantityof heat produced bycombustionalone was 2 ½ times greater than theamountofsolarenergy reaching the ground. In summer, the figure dropped to 1/6.

There are other,somewhatlessinfluential, causes of the heat island. For example, the blanket of pollutants over a city contributes to the heat island by absorbing aportionof the upward-directed long-waveradiationemitted at the surface and re-emitting some of it back to the ground. Asomewhatsimilar effect results from thecomplexthree-dimensional structure of the city. Theverticalwalls of office buildings, stores, and apartments do not allowradiationto escape asreadilyas inoutlyingrural areas where surfaces arerelativelyflat. As the sides of these structuresemittheir stored heat, aportionis re-radiated between buildings rather than upward, and isthereforeslowly dissipated. In addition to re-radiating the heat loss from the city, tall buildings alsoalterthe flow of air. Because of the greater surface roughness, wind speedswithinanurbanarea are reduced. Estimates from available records suggest a decrease on the order of about 25 percent from rural values. Thelowerwind speeds decrease the city’s ventilation by inhibiting the movement of cooler outside air which, if allowed topenetrate, would reduce the higher temperatures of the city center.

Questions:
question_stem: The word “proximity” in the passage is closest in meaning to
choices: tag: A
text: distribution

tag: B
text: contamination

tag: C
text: exposure

tag: D
text: closeness
answer_key: D
explanation: proximity=closeness 接近，临近。

question_stem: What can be inferred from paragraph 2 about the phenomenon of the urban heat island?
choices: tag: A
text: It occurs in rural areas to the same extent as urban areas.

tag: B
text: It is influenced by variations in weather.

tag: C
text: It increases the cloud cover over the city.

tag: D
text: It produces a lot of wind at night.
answer_key: B
explanation: 根据文段最后2句话：在晴朗的夜晚，城市和乡下温差高达11度甚至更多，而在多云或者有风的夜晚，温差接近0度，可知城市热岛效应受天气的影响，选 B；A 城市和乡下热岛效应程度一样，错误；C 和 D 跟最后一句话冲突。

question_stem: According to paragraph 2, temperatures in the city and the surrounding areas are likely to be about the same
choices: tag: A
text: during the months of December through February

tag: B
text: when averaged over a five-year span

tag: C
text: on clear, calm nights

tag: D
text: on cloudy, windy nights
answer_key: D
explanation: 根据最后一句话，可知，在有风或者多云的夜晚，城市乡下温差为0，选择 D。

question_stem: Which of the following is NOT mentioned in paragraph 3 as a contributing cause of urban heat islands?
choices: tag: A
text: The effects of tall buildings and hard surfaces

tag: B
text: The effects of vegetation on soil

tag: C
text: The rapid runoff of water

tag: D
text: The slow loss of nighttime heat
answer_key: B
explanation: A 对应 first 那句；C 对应 in addition 那句，D 对应最后一句；B 选项错误，跟文章 First 那句冲突：vegetation 属于 rural areas 的，不利于热岛效应的产生，选它。

question_stem: What can be inferred from paragraph 3 about rainwater in rural areas as compared to urban areas?
choices: tag: A
text: The evaporation rate of rainwater in rural areas is greater than it is in urban areas.

tag: B
text: The runoff of rainwater is more rapid in rural areas than it is in urban areas.

tag: C
text: Rural areas require more rainwater in order to cool down than urban areas do.

tag: D
text: Rural areas experience greater problems when rainwater evaporates than urban areas do.
answer_key: A
explanation: 根据文段 in addition 那句可知：城市表面水无法渗透，导致 water runoff 速度快，进而减少了蒸发率，反推，rural areas 蒸发率比城市更高，对应 A；B 选项 more rapid in rural areas 跟原文相反，C 和 D 对比都未提及。

question_stem: What purpose does paragraph 4 serve in the larger discussion of temperatures within urban areas?
choices: tag: A
text: To argue that certain urban areas produce more waste heat than others

tag: B
text: To examine the impact of solar radiation on temperatures in large urban areas

tag: C
text: To show how human-generated energy contributes to the urban heat island effect

tag: D
text: To point out the rate at which urban heat islands have increased over time
answer_key: C
explanation: 段落目的，找该段落的主旨句，对应文段第1和2句话：人为产生的 energy 会导致城市的热岛效应，对应 C 选项。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Pollutants hanging over a city contribute to the urban heat island effect by forcing solar radiation directly upward from the surface of Earth.

tag: B
text: Air pollution contributes to rising temperatures in cities by reflecting a certain amount of radiation it has absorbed from Earth’s surface first back to Earth.

tag: C
text: Earth’s surface absorbs long-wave radiation that is emitted by polluted air in Earth’s atmosphere.

tag: D
text: Earth sends some of the heat that it has absorbed into the air where it is then absorbed by pollutants.
answer_key: B
explanation: 原句子核心意思：污染物会通过吸收部分表面发出的长波辐射并且把部分长波辐射返回地面来导致热岛效应，A 选项 by 后面内容对应不上，错误；B 选项符合原句子意思可以入选；C 选项主干没有涵盖到与句子的核心错误；D 选项主干也没有包含原句子的核心，排除。

question_stem: According to paragraph 5, which of the following statements is true about air flowing through a city?
choices: tag: A
text: Its speed is comparable to that in the countryside.

tag: B
text: The movement of air is reduced by urban buildings.

tag: C
text: It allows the city to cool down thoroughly at night.

tag: D
text: It penetrates most quickly in urban areas with the tallest buildings.
answer_key: B
explanation: 根据题干关键词 air flowing 定位句从 in addition to re-redating 到文段最后：高楼会改变空气流动，因为高楼表面粗糙，风速会降低，低风速会减少城市通风。对应 B 选项。A 选项 comparable to 错误；C 选项 cool down 错误，penetrate most quickly 未提及。