Urban Heat Island 城市熱島效應web5.arch.cuhk.edu.hk/server1/staff2/szewai/KT_web/en/KT...Anthropogenic heat generated by energy consumed in the course of urban activities-especially

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School of Architecture, The Chinese University of Hong KongWorkshop on Urban Climatic for Design and Planning 5 & 12 June 2010

Urban Heat Island 城市熱島效應



City changes the energy balance of the local climate


City changes the energy balance of the local climate

On the whole there is a positive energy balance in the city

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http://www.albertasbestroof.com/images/stories/green-roofing/heat-island.jpgC

What is urban heat island? 什麼是城市熱島效應？

An urban heat island is the name given to describe the characteristic warmth of boththe atmosphere and surfaces in cities (urban areas) compared to their (non-urbanized) surroundings.



Rural Urban

Q*

QH

QE

QG

RSL

DayQ*

QH

QEΔQSQF

Rural Urban

Q*QH QE

QG

RSL

Night

Q*QH QE ΔQSQF

Oke, Unpubl.

Canyon (UCL) Air Temp changes

The Main Cause of UHI Formation 城市熱島效應成因


• Reduced vegetation in urban areas

• Properties of urban materials

• Urban geometry

• Anthropogenic heat

The Main Cause of UHI Formation 城市熱島效應成因

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A sky view in Hong Kong’s typical street canyon

UHI vs Sky View Factor (SVF)城市熱島效應與天空可見度的關係


Correlation of ∆T and 150m radius neighbourhood average SVF value.

UHI vs Sky View Factor (SVF)城市熱島效應與天空可見度的關係


Anthropogenic Heat 人工廢熱

Anthropogenic heat generated by energy consumed in the course of urban activities-especially by buildings, traffic, and industry plays an important role in urban climate. It is one of the main causes of the urban heat island effect, which is responsible for numerous severe problems in urban areas.


Case Study in Singapore

Singapore

City Area: 710.2sq.KmPopulation: 4.9 millionsLocation: CostalTopographical: flat

Climate: Tropicalsummer: warmwinter: warm

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(Wong, 2004)



Two major strategies to reduce the UHI effect exist:

• Introduce more green areas into the built environment (Plants serve to filter carbon dioxide and other toxins)

• Involve choosing proper building materials. (using light-coloured roofing material or reflective coatings lowers indoor and surrounding temperatures.)

(Wong, 2004)


Case Study in New York

New York, US

City Area: 141,299 sq.KmPopulation: 19.5 millionsLocation: CostalTopographical: flat

Climate: Sub-tropic summer: warm, humidwinter: mild



Rosenzweig, C.E., & Soleki, W.D. 2006. Mitigation New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces, New York City Regional Heat Island Initiative, The New York State Energy Research and Development Authority, Albany, New York.

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Stuttgart, Germany

City Area: 207.36 sq.KmPopulation: 0.59 millionsLocation: InlandTopographical: in a Valley

Climate: Temperate summer: warmwinter: mild

(Baumüller, et al., 1998)

Case Study in Stuttgart





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City Area: 2,187.08 sq.KmPopulation: 12.57 millionsLocation: CoastalTopographical: Flat

Climate: Temperatesummer: warm and humidwinter: cold

End to End- From Tradition to the New Frontier

CUHK Interdisciplinary Architectural Postgraduate Workshop 2008

Case Study in Tokyo


Case Study in Tokyo


Case Study in Tokyo


Case Study in Tokyo

Tokyo Wall

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Case Study in Tokyo


1952

2007

With fast urbanization, it brings about local climate changes in Hong Kong.


Measuring Urban Heat Island - Some Studies in Hong Kong


The conceptual character of Hong Kong urban geometry and heat generating process, Modified after Emmanuel,1997

(Giridharan et al., 2005)

Hong Kong has high density urban context. The typical buildings in Hong Kong are high rise and the H/W ratio is narrow. Some wind-blocking buildings at the seafront block the wind penetration and reduce wind speed. This special urban context deteriorates the urban living condition and intensifies the Urban Heat Island .

Hong Kong

Thermal image (Winter night)(South China Morning Post, 11 March 2007)


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ASTER scene-corrected image of Surface Temperature

(Nichol, 2005)

Local researchers carried out various studies to analysis UHI in Hong Kong.The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and MicroMeteorological Measurement Study.

Hong Kong

Cooling Effectof urban park and vegetated slopes at night



The difference of Air Temperature between rural and urban in HK (HKO Report, 2008)

Local researchers carried out a serious studies to analysis UHI in Hong Kong.The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and Micro Meteorological Measurement Study.

Hong Kong

0.80.71.41.81.41.00.70.60.50.50.40.30.4Average daily Tu-r

2.21.92.93.73.22.62.11.91.91.81.61.41.3Mean Tu-r at 6 am

2.82.53.64.43.83.22.72.52.52.32.11.92.0Daily mean Tu-r

11.59.111.011.510.37.96.54.54.94.75.66.88.9Daily

maximum Tu-r

211211109876543

WinterAutumnSummerSpring Y

Month

Tu-r



Temperature distribution along the route on the afternoon of summer day

(Fung, 2004)


Hong Kong

The UHI values in different periods(Fung, 2004)

Hottest regions in HK: The Kowloon Peninsular & The northern part of Hong Kong Island

The maximum UHI values in summer occurred in the morning while in winter it occurred at night .



The Map of Air Temperature Distribution for Tsim Sha Tsui site in a summer afternoon


Hong Kong

Ta Difference is about 3 - 4 ºC from seaside to inner site


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What are the Problems with the "Heat Island Effect?"

May be for our mom, there is no problem. She may use the heat for cooking!


Then, what are real problems?


The Consequences of UHI

Hot climateCold climateImpact

UHI circulation, breezes, stability, turbulence, convergence, uplift, mixed layer depth, cloud, precipitation, relative humidity, dewfall, evaporation, fog, visibility, snow, ‘contamination’ of long-term temperature records

Meteorological impacts

Not applicablePositiveIce and snow

Probably neutral except diseasePositiveBiological activity

NegativeNegativeWater use

Both positive and negativeBoth positive and negativeAir pollution dispersion

NegativeNegativeAir pollution chemistry

Negative (summer)

Negative (all seasons)Positive (winter)Energy use

Negative (summer)Negative (all seasons)Positive (winter)Human comfort

& mortality

Socio-economic and health impacts

Impacts of urban heat island (UHI) in cold and hot climate urban environments(Oke, 2002)


The Main Impacts in Hong Kong

Human comfort & mortality

Energy Use

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Increase of Very Hot Days and Very Hot Nights due to intra-urban temperature rises of 3 degree C.


Urban Climate

City location• climate• topography• rural surrounds

Weather• wind• cloud• stability

City form• fabric• structure• cover

City size• fetch distance• density of use

Time• day• season

City metabolism• energy/water use• waste emissions

Oke, 1980, unpubl.

How could people mitigate the UHI?

How to Control or Mitigate the "Heat Island Effect?"


Possible Planning Measures Learned from the WorldObjectives

UHIThermal

Load

+

WindDynamic Potential

Material & Surface Level Intervention

Building Level Intervention

Urban & Planning Level Intervention

Macro Effect

Micro Effect

Short time

Long time

Planning Time Scale Spatial Scale

Albedo• Cool building-material &

pavement;• Cool roof & facade; • Water retention paving;

Vegetation

Shading

Ventilation

• Planting & greeneries;• Parks & open spaces;

• Building geometric design;• Shelter design;• Street orientation;• H/W ratio;• Trees;

• Air paths;• Building ground cover

& building bulks;• H/W ratio;• Street orientation;• Open spaces;• Building disposition;

Strategies Planning Actions


Controls on UHI effects

(Mochida, 2007)

• Change albedo

• Increase vegetation

• Provide shading

• Improve ventilation

Cool roof coatings.(US. EPA, 2007)

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(Mochida, 2007)

• Change albedo


• Provide shading


The distribution of air temperature for the area of a large park and its surroundings in Montreal, Canada (Marsh, 1991)



(Mochida, 2007)

• Change albedo


• Provide shading


Tree’s effect.(US EPA, 2007)



(Mochida, 2007)

• Change albedo


• Provide shading


(Ng, 2006)


Hong Kong

5嵗小孩的素描, “我的香港”。A sketch by a 5 years old, titled “my Hong Kong”.

將來的環境是怎樣的?What will be the environmental future of Hong Kong?

我們的子女將生活在怎樣的將來?What kind of Hong Kong our sons and daughters will live?

Thank you for listening

Documents

Urban Heat Island 城市熱島效應web5.arch.cuhk.edu.hk/server1/staff2/szewai/KT_web/en/KT...Anthropogenic heat generated by energy consumed in the course of urban activities-especially