Urban Heat Island Effect (??????)

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Urban Heat Island Effect (??????)
The Hong Kong Polytechnic University Department
of Applied Physics
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What is Urban Heat Island Effect?

• The temperature in cities is higher than the
  suburbs (??)
• The temperature in cities is higher and so
  isotherm (???) decreases gradually from the
  cities to the surrounding suburbs (??).
• The city seems to be an island in relief map
  (???) surrounded by the suburb ocean, so it is
  called Heat Island (??).

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Urban Heat Island Effect

• Hot air in city continuously flows up and
  disperse at a certain height in the sky, forming
  low pressure area (???) on ground.
• Cool air on ground from suburbs flows into the
  city causing circumfluence (??).
• Smoke and dust from industrial areas (???) around
  the city flow into the town centre instead,
  causing the concentration of pollutants in town
  center higher than that of the industrial area.

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Urban Heat Island Effect
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Urban Island Effect in Hong Kong
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Causes (??) of Urban Heat Island Effect

• Buildings highly concentrated in cities
• Low wind speed near ground level
• Poor ventilate (??)
• Artificial environment absorbs much radiation
• from the Sun
• Multiple reflection and absorption between roofs,
  walls of buildings and the ground
• Large heat capacity (???) of reinforced concrete
  (????) absorbs much radiation during daytime
• Heat release due to human activities
• heat emission by air-conditioners and cars
• Air pollution
• Such pollutants absorb radiation heat easily

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Influence (??) ofUrban Heat Island Effect

• The strength of Urban Heat Island Effect is
• related to the scale of the city (????),
  meteorology factors (????), etc.
• The annual mean temperature (?????) of big cities
  is 0.5 1 C higher than that of suburbs
• The lowest mean temperature (??????) of big
  cities in winter is 1 2 C higher than that of
  suburbs
• Cities seems like a warm island, Urban Heat
  Island Effect is more apparent in big cities and
  at night.

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Influence (??) ofUrban Heat Island Effect
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Influence (??) ofUrban Heat Island Effect

• Weaken the intensity of solar radiation (????)
  and sunshine (??)
• Dust in the air is increasing due to air
  pollution. Therefore, solar radiation reaching
  the ground is weakened.

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Influence (??) of Urban Heat Island Effect

• Low humidity (??), foggy (??), rainfall (??)
  increases
• Cities with good drainage system (????) and
  concrete ground causing humidity of cities lower
  than that of suburbs.
• The ground is dry. It cannot help accommodating
  weather.
• There are many cloud condensation nuclei (???) in
  the sky above the cities, so it is foggy.
• The annual rainfall (????) in cities is about 5
  10 higher than that of the suburbs.

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Urban Heat Island Effect aggravated (??) by
Urbanization (???)

• Development of cities accelerates the changes of
  climate
• rapid urbanization in Hong Kong in recent 50
  years causing the warmer climate
• the temperature rises 1 C in average

• Reasons
• A large number of trees are chopped, fewer plants
  to remove carbon dioxide (????) and to adsorb
  (??) dust
• Density and height of buildings increases, so
  wind cannot flow into cities
• Exhaust (??) discharged from air-conditioners and
  cars