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”.

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

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

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

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

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

15. Green House Effect

17. 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

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

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

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

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

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

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

25. Magnitude of Heat Island

26. 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 )

27. Temperature distribution within a city
Vertical distribution
Normal
Inversion

28. Temperature distribution within a city
Inversion and Pollution

29. Temperature distribution within a city
Dust Dome / Pollution Dome

30. The End