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City Climate

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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  1. City Climate The Heat Island Effect HO Pui-sing

  2. City Climate • City Climate as a micro-climate • Micro-climate is a climate conditions of the nearest 100m of the ground surface.

  3. 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”.

  4. The Heat Island Effect • Causes of the heat island • Magnitude of the head island • Temperature distribution within a city

  5. Causes of the Heat Island • Changes of surface • Heat Production • Changes in the composition of atmos. • Increase Turbidity

  6. Causes of the Heat Island • Changes of surface • Waterproof cement surface • Thermal Admittance • Roughness of the surface

  7. Causes of the Heat Island • Heat Production • Industrial Activities • Cooling and Heating • Concentration of People

  8. Causes of the Heat Island • Changes in the composition of atmosphere • Increase green-house gases – CO2, CO • Enhance green-house effect

  9. Green House Effect

  10. 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

  11. Magnitude of Heat Island • Size of cities • Local Micro-climate condition • Topography • Diurnal and Weekly variation • Seasonal variation • Building density • Distance from city

  12. Magnitude of Heat Island • Size of cities • Large city – strong heat island effect • Small city – weak heat island effect

  13. Magnitude of Heat Island • Local Micro-climate condition • Wind speed • fast – weak effect • Slow – strong effect • Cloud cover • High - strong effect • Low – weak effect

  14. Magnitude of Heat Island • Topography • The effect will be less pronounced among ocean, rivers, lakes, wood land, pastures and areas of high elevation

  15. Magnitude of Heat Island • Diurnal and weekly variation • More pronounced at night and during week days • Seasonal variation • More pronounced during winter

  16. Magnitude of Heat Island • Building density • Magnitude increases with increasing building density • Distance from city centre • Magnitude increases with decreasing distance from city centre

  17. Magnitude of Heat Island

  18. 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 )

  19. Temperature distribution within a city • Vertical distribution Normal Inversion

  20. Temperature distribution within a city • Inversion and Pollution

  21. Temperature distribution within a city • Dust Dome / Pollution Dome

  22. The End

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