City climate
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City Climate. The Heat Island Effect. HO Pui-sing. City Climate. City Climate as a micro-climate Micro-climate is a climate conditions of the nearest 100m of the ground surface. Heat Island. Temperature of cities is higher than the temperature of the surrounding areas.

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City Climate

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City climate

City Climate

The Heat Island Effect

HO Pui-sing


City climate1

City Climate

  • City Climate as a micro-climate

  • Micro-climate is a climate conditions of the nearest 100m of the ground surface.


City climate

Heat Island

  • Temperature of cities is higher than the temperature of the surrounding areas.

  • Showing by isotherm, it looks like a “warm island” surrounded by a “cool sea”.


The heat island effect

The Heat Island Effect

  • Causes of the heat island

  • Magnitude of the head island

  • Temperature distribution within a city


Causes of the heat island

Causes of the Heat Island

  • Changes of surface

  • Heat Production

  • Changes in the composition of atmos.

  • Increase Turbidity


Causes of the heat island1

Causes of the Heat Island

  • Changes of surface

    • Waterproof cement surface

    • Thermal Admittance

    • Roughness of the surface


Causes of the heat island2

Causes of the Heat Island

  • Heat Production

    • Industrial Activities

    • Cooling and Heating

    • Concentration of People


Causes of the heat island3

Causes of the Heat Island

  • Changes in the composition of atmosphere

    • Increase green-house gases – CO2, CO

    • Enhance green-house effect


Green house effect

Green House Effect


Causes of the heat island4

Causes of the Heat Island

  • Increase Turbidity

    • Industrial and transport activities introduce a great quantity of fine particles into the air.

    • Increase the counter-radiation

    • Hinder heat dispersion


Magnitude of heat island

Magnitude of Heat Island

  • Size of cities

  • Local Micro-climate condition

  • Topography

  • Diurnal and Weekly variation

  • Seasonal variation

  • Building density

  • Distance from city


Magnitude of heat island1

Magnitude of Heat Island

  • Size of cities

    • Large city – strong heat island effect

    • Small city – weak heat island effect


Magnitude of heat island2

Magnitude of Heat Island

  • Local Micro-climate condition

    • Wind speed

      • fast – weak effect

      • Slow – strong effect

    • Cloud cover

      • High - strong effect

      • Low – weak effect


Magnitude of heat island3

Magnitude of Heat Island

  • Topography

    • The effect will be less pronounced among ocean, rivers, lakes, wood land, pastures and areas of high elevation


Magnitude of heat island4

Magnitude of Heat Island

  • Diurnal and weekly variation

    • More pronounced at night and during week days

  • Seasonal variation

    • More pronounced during winter


Magnitude of heat island5

Magnitude of Heat Island

  • Building density

    • Magnitude increases with increasing building density

  • Distance from city centre

    • Magnitude increases with decreasing distance from city centre


Magnitude of heat island6

Magnitude of Heat Island


Temperature distribution within a city

Temperature distribution within a city

  • Variation within a city / Horizontal distribution

    • Street intersection – (the coldest place)

    • Heavily traveled main roads (2 degree )

    • Around stop light (2-3 degree )


Temperature distribution within a city1

Temperature distribution within a city

  • Vertical distribution

Normal

Inversion


Temperature distribution within a city2

Temperature distribution within a city

  • Inversion and Pollution


Temperature distribution within a city3

Temperature distribution within a city

  • Dust Dome / Pollution Dome


City climate

The End


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