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City Climate

The Urban Heat Island (UHI) effect describes how cities experience higher temperatures than their surrounding areas, creating a “warm island” amid a “cool sea.” This phenomenon is influenced by factors such as surface changes, heat production from human activities, and increasing greenhouse gas emissions. The magnitude of the UHI is determined by city size, building density, topography, and seasonal variations. Understanding these elements is vital for developing strategies to mitigate UHI impacts and enhance urban resilience against climate challenges.

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City Climate

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Presentation Transcript

  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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