results when rural areas are transformed into cities
is a significant cause of the rise in temperature in cities
that is known as 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 concrete and asphalt are
impermeable, the runoff of water following a rain
is rapid, resulting in a severe reduction in the
evaporation rate. So heat that once would have
been used to convert liquid water to a gas goes
instead to increase the surface temperature further.
At night, although both city and countryside cool
through radiation losses, the stonelike surface
of the city gradually releases the additional heat
accumulated during the day, keeping the urban air
warmer than that of the outlying areas.
Part of the urban temperature rise must also
be attributed to waste heat from such sources as
home heating and air conditioning, power generation,
industry, and transportation. Many studies have
shown that the magnitude of human-made energy in
metropolitan areas is equal to a significant percentage
of the energy received from the Sun at the surface.
Investigations in Sheffield, England, and Berlin
showed that the annual heat production in these cities
was equal to approximately one-third of that received
from solar radiation. Another study of the densely
built-up Manhattan section of New York City revealed
that during the winter the quantity of heat produced
from combustion alone was two and one-half times
greater than the amount of solar energy reaching the
ground. In summer the figure dropped to one-sixth.
It is interesting to note that during the summer there is
a mutual reinforcement between the higher nighttime
temperatures of the city and the human-made heat that
helped create them. That is, the higher temperatures
result in the increased use of air conditioners, which, in
turn, use energy and further increase the amount of
urban heat. During the winter the nighttime warmth of
urban areas, produced in large part by heavy energy
consumption, is beneficial because less energy is
needed to heat buildings.
275. Which of the following is true about
cities at night in the winter?
A. Solar energy has an increased
impact on the urban heat island.
B. They tend to be colder than rural areas.
C. Less energy is required to heat buildings.
D. Human-made energy creates a larger area of
total heat than solar energy.
PP伴侶的答案是D，但有的版本答案是C，
我從紅色線部分作答，所以我選C，不知各位想法？
