Urban Heat Island 城市熱島效應

Transcription

1 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 1

2 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 both the atmosphere and surfaces in cities (urban areas) compared to their (non-urbanized) surroundings. The Main Cause of UHI Formation 城市熱島效應成因 The Main Cause of UHI Formation 城市熱島效應成因 Oke, Unpubl. Day Q* Q E Q H Q G Rural Q* Q F ΔQ S Urban Q H Q E RSL Canyon (UCL) Air Temp changes Reduced vegetation in urban areas Properties of urban materials Urban geometry Anthropogenic heat Night Q* Q* Q H QE ΔQ S Q H QE Q F RSL Q G Rural Urban 2

3 UHI vs Sky View Factor (SVF) 城市熱島效應與天空可見度的關係 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. A sky view in s typical street canyon Anthropogenic Heat 人工廢熱 Case Study in Singapore Anthropogenic heat generated by energy consumed in the course of urban activitiesespecially 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. Singapore City Area: 710.2sq.Km Population: 4.9 millions Location: Costal Topographical: flat Climate: Tropical summer: warm winter: warm 3

4 Case Study in Singapore Case Study in Singapore 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) (Wong, 2004) Case Study in New York Case Study in New York New York, US City Area: 141,299 sq.km Population: 19.5 millions Location: Costal Topographical: flat Climate: Sub-tropic summer: warm, humid winter: mild Rosenzweig, C.E., & Soleki, W.D 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. 4

5 Case Study in New York Case Study in Stuttgart Stuttgart, Germany City Area: sq.km Population: 0.59 millions Location: Inland Topographical: in a Valley Climate: Temperate summer: warm winter: mild (Baumüller, et al., 1998) Case Study in Stuttgart Case Study in Stuttgart 5

6 Case Study in Tokyo Case Study in Tokyo City Area: 2, sq.km Population: millions Location: Coastal Topographical: Flat Climate: Temperate summer: warm and humid winter: cold End to End- From Tradition to the New Frontier CUHK Interdisciplinary School of Architecture, Architectural The Chinese University Postgraduate of Workshop 2008 Case Study in Tokyo Case Study in Tokyo Tokyo Wall 6

7 Case Study in Tokyo With fast urbanization, it brings about local climate changes in 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. The conceptual character of urban geometry and heat generating process, Modified after Emmanuel,1997 (Giridharan et al., 2005) Thermal image (Winter night) (South China Morning Post, 11 March 2007) 7

8 Local researchers carried out various studies to analysis UHI in. The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and Micro Meteorological Measurement Study. Local researchers carried out a serious studies to analysis UHI in. The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and Micro Meteorological Measurement Study. Month T u-r Spring Summer Autumn Winter Y Daily maximum Cooling Effect of urban park and vegetated slopes at night T u-r Daily mean T u-r Mean T u-r at 6 am Average daily T u-r ASTER scene-corrected image of Surface Temperature (Nichol, 2005) 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. The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and Micro Meteorological Measurement Study. Local researchers carried out a serious studies to analysis UHI in. The methods they used include Remote Sensing Image, Historical Meteorological Data Analysis, Mobile Measurement Study and Micro Meteorological Measurement Study. The maximum UHI values in summer occurred in the morning while in winter it occurred at night. Hottest regions in HK: The Kowloon Peninsular & The northern part of Island Ta Difference is about 3-4 ºC from seaside to inner site The UHI values in different periods (Fung, 2004) Temperature distribution along the route on the afternoon of summer day (Fung, 2004) The Map of Air Temperature Distribution for Tsim Sha Tsui site in a summer afternoon 8

9 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 The Main Impacts in Impacts of urban heat island (UHI) in cold and hot climate urban environments (Oke, 2002) Impact Socio-economic and health impacts Human comfort & mortality Energy use Air pollution chemistry Cold climate Positive (winter) Negative (summer) Positive (winter) Negative (summer) Negative Hot climate Negative (all seasons) Negative (all seasons) Negative Human comfort & mortality Air pollution dispersion Both positive and negative Both positive and negative Water use Negative Negative Biological activity Positive Probably neutral except disease Ice and snow Positive Not applicable Meteorological impacts 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 Energy Use 9

10 Increase of Very Hot Days and Very Hot Nights due to intra-urban temperature rises of 3 degree C. How to Control or Mitigate the "Heat Island Effect?" Time day season City location climate topography rural surrounds City size fetch distance density of use Oke, 1980, unpubl. Urban Climate City metabolism energy/water use waste emissions Weather wind cloud stability City form fabric structure cover How could people mitigate the UHI? Possible Planning Measures Learned from the World Controls on UHI effects Objectives UHI Thermal Load + Wind Dynamic Potential Strategies Albedo Vegetation Shading Ventilation Planning Actions Cool building-material & pavement; Cool roof & facade; Water retention paving; 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; Planning Time Scale Short time Material & Surface Level Intervention Building Level Intervention Urban & Planning Level Intervention Long time Spatial Scale Macro Effect Micro Effect Change albedo Increase vegetation Provide shading Improve ventilation Cool roof coatings. (US. EPA, 2007) (Mochida, 2007) 10

11 Controls on UHI effects Controls on UHI effects Change albedo Change albedo Increase vegetation Increase vegetation Provide shading Provide shading Improve ventilation Improve ventilation The distribution of air temperature for the area of a large park and its surroundings in Montreal, Canada (Marsh, 1991) (Mochida, 2007) Tree s effect. (US EPA, 2007) (Mochida, 2007) Change albedo Increase vegetation Provide shading Improve ventilation Controls on UHI effects 將來的環境是怎樣的? What will be the environmental future of? 我們的子女將生活在怎樣的將來? What kind of our sons and daughters will live? 5 嵗小孩的素描, 我的香港 A sketch by a 5 years old, titled my. (Ng, 2006) (Mochida, 2007) Thank you for listening 11