本篇文章共分 5 段，針對都市地區比周圍郊區或鄉村溫度較高所顯現的都市熱島效應做說明，提出影響都市熱島效應的主要與次要因素，分別敘述其影響的效果。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

Urban Heat Islands 都市熱島

1. 都市熱島的形成原因

   Climatic changes such as changes in temperature, precipitation, humidity, or wind speed that are produced by urbanization involve all major surface conditions. Some of these changes are quite obvious and relatively easy to measure. Others are more subtle and sometimes difficult to measure. The amount of change in any of these elements, at any time, depends on several variables, including the extent of the urban complex, the nature of industry, site factors such as topography and proximity to water bodies, time of day, and existing weather conditions.

   氣候的變化，如溫度、降水、濕度或風速的變化，是由城市化產生的，涉及所有主要的地表條件。其中一些變化是相當明顯的，相對容易測量。其他的則比較微妙，有時難以測量。任何時候，這些元素的變化量都取決於幾個變量，包括城市綜合體的範圍、工業的性質、場地因素，如地形和靠近水體、一天中的時間和現有的天氣條件。

2. 都市熱島現象

   The most studied and well-documented urban climatic effect is the urban heat island. The term simply refers to the fact that temperatures within cities are generally higher than in rural areas. The heat island is evident when temperature data are examined. For example, the distribution of average minimum temperatures in the Washington, D.C., metropolitan area for the three-month winter period (December through February) over a five-year span, 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 average minimum temperatures that were as much as 3.3°C lower. Remember that these temperatures are averages, because on many clear, calm nights the temperature difference between the city center and the countryside was considerably greater, often 11°C or more. Conversely, on many overcast or windy nights the temperature differential approached zero degrees.

   研究和記錄最多的城市氣候效應是城市熱島。這個術語只是指城市內的溫度通常高於農村地區的事實。在檢查溫度數據時，熱島是很明顯的。例如，華盛頓特區大都會地區五年來冬季三個月期間（12 月至 2 月）的平均最低溫度的分佈，清楚地代表了一個發達的熱島。最溫暖的冬季溫度發生在城市中心，而郊區和周圍鄉村的平均最低溫度則會低 3.3℃。請記住，這些溫度是平均值，因為在許多晴朗、平靜的夜晚，市中心和鄉下的溫差要大得多，往往是 11℃或更高。相反，在許多陰天或有風的夜晚，溫差接近零度。

3. 建築物的影響

   The radical change in the surface that results when rural areas are transformed into cities is a significant cause of the urban heat island. First, the tall buildings and the concrete and asphalt of the city absorb and store greater quantities of solar radiation than do the vegetation and soil typical of rural areas. In addition, because the city surface is impermeable, the runoff of water following a rain is rapid, resulting in a severe reduction in the evaporation rate. Hence, heat that once would have been used to convert liquid water 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 the additional heat accumulated during the day, keeping the urban air warmer than that of the outlying areas.

   當農村地區被改造成城市時，地表的根本變化是城市熱島的一個重要原因。首先，與農村地區典型的植被和土壤相比，城市中的高大建築物以及混凝土和瀝青吸收並儲存了更多的太陽輻射。此外，由於城市的表面是不透水的，雨後水的徑流很快，導致蒸發率嚴重下降。因此，曾經用於將液態水轉化為氣體的熱量現在被用於提高地表溫度。在夜間，當城市和鄉村都因輻射損失而冷卻時，城市的石質表面逐漸釋放出白天積累的額外熱量，使城市的空氣比外圍地區的空氣更熱。

4. 能源使用的影響

   A portion of the urban temperature rise must also be attributed to waste heat from sources such as home heating and air conditioning, power generation, industry, and transportation. Many studies have shown that the magnitude of human-generated energy in metropolitan areas is great when compared to the amount of energy received from the Sun at the surface. For example, investigations in Sheffield, England, and Berlin, Germany, showed that the annual heat production in those cities was equal to approximately one-third of that received from solar radiation. Another study of densely built-up Manhattan in New York City revealed that during the winter, the quantity of heat produced by combustion alone was 2 times greater than the amount of solar energy reaching the ground. In summer, the figure dropped to 1/6.

   城市溫度上升的一部分也必須歸因於來自家庭供暖和空調、發電、工業和交通等來源的廢熱。許多研究顯示，與地表從太陽接收的能量相比，大都市地區人類產生的能量規模很大。例如，在英國謝菲爾德和德國柏林的調查顯示，這些城市每年產生的熱量相當於從太陽輻射獲得的熱量的三分之一左右。另一項對紐約市密集的曼哈頓的研究指出，在冬季，僅燃燒產生的熱量就比到達地面的太陽能多出 2 倍。在夏季，這個數字下降到 1/6。

5. 汙染物與結構物的影響

   There are other, somewhat less influential, causes of the heat island. For example, the blanket of pollutants over a city contributes to the heat island by absorbing a portion of the upward-directed long-wave radiation emitted at the surface and re-emitting some of it back to the ground. A somewhat similar effect results from the complex three-dimensional structure of the city. The vertical walls of office buildings, stores, and apartments do not allow radiation to escape as readily as in outlying rural areas where surfaces are relatively flat. As the sides of these structures emit their stored heat, a portion is re-radiated between buildings rather than upward, and is therefore slowly dissipated. In addition to re-radiating the heat loss from the city, tall buildings also alter the flow of air. Because of the greater surface roughness, wind speeds within an urban area are reduced. Estimates from available records suggest a decrease on the order of about 25 percent from rural values. The lower wind speeds decrease the city’s ventilation by inhibiting the movement of cooler outside air which, if allowed to penetrate, would reduce the higher temperatures of the city center.

   還有其他一些影響較小的熱島的原因。例如，城市上空的如毯子般的污染物吸收了一部分在地表發射的向上的長波輻射，並將其中一部分重新發射回到地面，從而增強了熱島效應。城市複雜的三維結構也產生了某種類似的效果。辦公樓、商店和公寓的垂直牆體不允許輻射像外圍的農村地區那樣容易逸出，那裡的表面相對平坦。當這些結構的側面排放其儲存的熱量時，一部分被重新輻射到建築物之間，而不是向上輻射，因此被緩慢地消散了。除了重新輻射來自城市的熱量損失外，高樓還改變了空氣的流動。由於更大的表面粗糙度，城市地區的風速會降低。根據現有記錄的估計，與農村的數值相比，風速下降了大約 25%。較低的風速抑制了外部冷空氣的流動，從而降低了城市的通風量，而這些外部冷空氣如果被允許穿透，將降低市中心的較高溫度。