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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. - PowerPoint PPT Presentation
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City Climate
The Heat Island Effect
HO Pui-sing
City Climate
City Climate as a micro-climateMicro-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.
Showing by isotherm, it looks like a “warm island” surrounded by a “cool sea”.
The Heat Island Effect
Causes of the heat islandMagnitude of the head islandTemperature distribution within a city
Causes of the Heat Island
Changes of surfaceHeat ProductionChanges in the composition of atmos.Increase Turbidity
Causes of the Heat Island
Changes of surfaceWaterproof cement surfaceThermal AdmittanceRoughness of the surface
Causes of the Heat Island
Heat ProductionIndustrial ActivitiesCooling and HeatingConcentration of People
Causes of the Heat Island
Changes in the composition of atmosphere
Increase green-house gases – CO2, COEnhance green-house effect
Green House Effect
Causes of the Heat Island
Increase TurbidityIndustrial and transport activities introduce a great quantity of fine particles into the air.Increase the counter-radiationHinder heat dispersion
Magnitude of Heat Island
Size of citiesLocal Micro-climate conditionTopographyDiurnal and Weekly variationSeasonal variationBuilding densityDistance from city
Magnitude of Heat Island
Size of citiesLarge city – strong heat island effectSmall city – weak heat island effect
Magnitude of Heat Island
Local Micro-climate conditionWind speed• fast – weak effect• Slow – strong effect
Cloud cover• High - strong effect• Low – weak effect
Magnitude of Heat Island
TopographyThe effect will be less pronounced among ocean, rivers, lakes, wood land, pastures and areas of high elevation
Magnitude of Heat Island
Diurnal and weekly variationMore pronounced at night and during week days
Seasonal variationMore pronounced during winter
Magnitude of Heat Island
Building densityMagnitude increases with increasing building density
Distance from city centreMagnitude increases with decreasing distance from city centre
Magnitude of Heat Island
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 city
Vertical distribution
Normal Inversion
Temperature distribution within a city
Inversion and Pollution
Temperature distribution within a city
Dust Dome / Pollution Dome
The End
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