Environmental Impacts of Urban Heat Islands and their Countermeasures - Experiences of Japanese dense cities-

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1 1 PGBC Symposium on Green Building in Hong Kong December 2, 2006 Environmental Impacts of Urban Heat Islands and their Countermeasures - Experiences of Japanese dense cities- Akashi Mochida and Isaac Y.F. Lun Department of Architecture & Building Science Tohoku University Sendai, Japan

2 2 Outline of the presentation 1. Impacts of Urban Heat Islands on Living Environment in Tokyo 2. Mechanism causing Urban Heat Islands and their Countermeasures 3. Implementation of Policies for Heat-Island Mitigation by Japanese Central Government 4. Implementation of Policies for Heat-Island Mitigation by Local Government of Tokyo 5. Suggestions by AIJ ( Architectural Institute of Japan)

3 Temperature rises in major cities around the world (Murakami) (Source: Japan Meteorological Agency) Annual mean temperature [ o C] Tokyo New York Paris 8.0 World mean temperature

4 4 Temperature increase due to urbanization, i.e. urban heat island effect, is becoming serious in Japan temperature The pace of global warming year Increase of air temperature in Tokyo from 1880 (measured data, height about 1.5m) The temperature increased in Tokyo during the past 100 years is much more rapid than global temperature rise

5 5 Rise in daily maximum temperature in Tokyo area (August) (Source: Japan Meteorological Agency) Tokyo Bay (1) 1980 (2) 1990 (3) 2000 [ ]

6 Number of days on which daily minimum temperature at night-time exceeds 25 (Tropical night, Central Tokyo) [day] (Source: Japan Meteorological Agency) (Tropical night) [year] 6

7 Increased of heatstroke: Number of patients taken to hospital by ambulance service has increased over the years Number of patients Frequency of calling ambulance service (Source: Tokyo Fire Department) 7

8 8 Impact of 1 rise on energy consumption in Tokyo area ( summer ) (Murakami) 1 rise Equivalent to 1.8GW ( kw) of electricity (1) If covered by nuclear power generation two medium-sized nuclear reactors (2) Total cost is about $2.5 billion (Estimated by TEPCO; Tokyo Electric Power Co. Inc.)

9 9 Outline of the presentation 1. Impacts of Urban Heat Islands on Living Environment in Tokyo 2. Mechanism causing Urban Heat Islands and their Countermeasures 3. Implementation of Policies for Heat-Island Mitigation by Japanese Central Government 4. Implementation of Policies for Heat-Island Mitigation by Local Government of Tokyo 5. Suggestions by AIJ ( Architectural Institute of Japan)

10 Causes of the urban heat island (Ashie) Increase of anthropogenic heat releases from airconditioning, automobiles, etc. Low wind velocity due to the high density of urban structures Change of land surface covering (decrease of green and water space, but increase of hard surfaces such as buildings and roads) Decrease of evaporation from ground surface Land surface covering Anthropogenic heat Urban ventilation 10

11 Important Effects of Evaporation Large amount of heat can be consumed through evaporation from natural land covers such as trees, water space and natural soils etc. This effect significantly reduces the ambient air temperature. But, due to the results of urbanization, the area covered with natural land decreases remarkably and changes to asphalt and concrete covers. As a result, the effect of evaporation that reduces the temperature has been decreased. 11

12 Examples of countermeasures (1) Increase of evaporation from urban surfaces; greening on rooftops and building walls 12

13 公園公園Examples of countermeasures (1) Increase of evaporation from urban surfaces; Recover of green/water areas on the ground 園(Cross-sectional view) (Plan view) Greening and ventilation design around buildings arrangement of buildings and greenings should be planned simultaneously (effect of transporting cool air) 13

14 Examples of countermeasures (1) Increase of evaporation from urban surfaces; Water Retentive Pavement evaporation Raining heat release via evaporation 14

15 Examples of countermeasures (1) Increase of evaporation from urban surfaces; Road Surface Watering (Shiodome District) Watering tube Water retentive pavement nozzle Reclaimed water 15

16 Examples of countermeasures (2) Sunshade for pedestrian spaces; Creation of shade by planting trees (Solar radiation) Large heat accumulation within a building Large incoming radiation into body Reduced heat accumulation within a building Reduced incoming radiation to body Large heat accumulation in ground Reduced heat accumulation in ground Reduced surface temperature (1)Without trees (2)With trees 16

17 Examples of countermeasures (3) Use highly reflective painting ( materials ) and increase the reflected solar radiation ( Cool Roof ) Reflected solar radiation: Low Reflected into space Reflected solar radiation: High non-reflective painting on the roof Large cooling load reflective painting on the roof Reduced cooling load Return as much solar heat as possible to space (->sky ) 17

18 Field Study of High Light-Reflective Painting Without Painting HLRP D HLRP C Normal Painting HLRP E Room G (Normal Paint) Room F (No Paint) HLRP B HLRP A Room E (HLRP E) Room D (HLRP D) Room C (HLRP C) Room B (HLRP B) 62.0 ( ) Source: The Tokyo Metropolitan Research Institute for Environmental Protection Room A (HLRP A) Surface temperature by Thermograph (Aug 13th, 13:00)

19 Examples of countermeasures (4) Reduce anthropogenic heat releases from buildings Offices 20% Traffic 28% Others 2% TJ/d Buildings 50% It is important to reduce the energy consumption of buildings by applying various energy saving measures. Source: Research report on heat-island by Ministry of the Environment (2002) Composition ratio of anthropogenic heat release (Central Tokyo) 19

20 Examples of countermeasures (4) Reduce anthropogenic heat releases from buildings Reduce the impact of anthropogenic heat release in pedestrian spaces by considering the positions of heat release (1) Exhaust heat from walls (2) Exhaust heat from rooftops Reduction of heat impact upon pedestrian spaces 20

21 Examples of countermeasures(5) Urban ventilation; Improvement of ventilation in cities (1)Low-rise densely built-up areas air does not flow into pedestrian spaces ( 2 ) High-rise buildings with enough open-space good ventilation to ground level 21

22 Wind velocity is decreased due to densely constructed high-rise buildings Recently, many tall buildings have been constructed along the coastal areas in Tokyo. Tokyo(Shiodome district) In Shiodome district, it is reported that densely constructed tall buildings block the cold wind from Tokyo bay to blow into the areas behind the buildings. 22

23 Temperature is increased Sea breeze サンデー毎日 Tall buildings This problem has been reported on newspapers, magazines, TV programs and it becomes a big issue. 23

24 Careful design of building shapes and building layout considering the prevailing wind direction is required Buildings Buildings Prevailing wind Prevailing wind (1)Arranged at right angles to prevailing wind blocked (2)Arranged parallel with prevailing wind good ventilation 24

25 Situation in Hong Kong seems to be more serious than Tokyo! Tokyo(Shiodome district) Hong Kong 25

26 Development of Air Ventilation Assessment System in Hong Kong Recently, the research group directed by Prof. Edward Ng (Chinese University of Hong Kong) has carried out a research project to develop the assessment system of urban ventilation in Hong Kong ( AVAS ). This project will surely contribute to great improvement of urban environment in Hong Kong. 26

27 Outline of the presentation 1. Impacts of Urban Heat Islands on Living Environment in Tokyo 2. Mechanism causing Urban Heat Islands and their Countermeasures 3. Implementation of Policies for Heat-Island Mitigation by Japanese Central Government 4. Implementation of Policies for Heat-Island Mitigation by Local Government of Tokyo 5. Suggestions by AIJ ( Architectural Institute of Japan) 27

28 The Inter-Ministry Coordination Committee to Mitigate Urban Heat Island Effects was established in September 2002 The main task: to promote close communication and collaboration among ministries in implementing the comprehensive measures against urban heat islands The policy framework to reduce the heat island effects was announced in March

29 Outline of the Policy Framework to Reduce Urban Heat Island Effects (March 2004) Basic policies: - To strengthen measures step-by-step with flexible revisions based on long-term programs. - To carry out comprehensive and effective measures while monitoring urban thermal environment, analyzing factors and cobenefits. Measures against urban heat islands considered: - Reduction of anthropogenic heat emissions - Improvement of ground surfaces in urban areas - Improvement of urban structures - Change of lifestyle Strengthen monitoring and promote research Follow-up and review 29

30 In March 2004 The Japanese Government Committee on Urban Heat Island Effect announced an outline of countermeasures against heat islands ( ヒートアイランド対策大綱 ) In July 2004 Japanese Ministry of Land, Infrastructure and Transport (MLIT) issued the Building Design Guidelines for mitigating urban heat island effects to all prefecture governors ( 国土交通省 : ヒートアイランド対策のための建築設計ガイドライン ) 30

31 Building Design Guidelines to Mitigate Heat-Islands (July 2004) Aim: provide guidance of building design in the following items 1) Ventilation Channeling of wind into pedestrian spaces within building sites, and avoidance of blocking of wind passages 2) Shading Creation of shade in summer and mitigation of summer heat in pedestrian spaces within sites 3) Ground level covering Provision of green spaces and water spaces within building sites to prevent ground-level temperature rise 4) Building cladding materials Reduction of the load on the air-conditioning and thermal impact on pedestrian spaces and adjacent areas by improving the performance of building cladding materials 5) Exhaust heat from building facilities Reduction of emissions of anthropogenic heat into pedestrian spaces and adjacent areas 31

32 An example of building design based on Building Design Guidelines to Mitigate Heat-islands (July 2004) Shading Tree planting Piloti, eaves, pergola Ground level covering Greenery and Water Reducing amount of pavement Building cladding materials Roof materials which reflect sunlight Greening of roofs and walls Green area Sunlight Roof garden Greening of walls Open space Shading Water surface Heat emissions Wind flow planning Ventilation Green areas and paths Building layout to ensure wind flow Anthropogenic heat from building facilities Reducing heat emissions by high heat insulation and highly efficient building facilities Heat emissions through upper parts 32

33 Development of rating tool for evaluating countermeasures of heat-island mitigation Building Design Guidelines (by MLIT) It is qualitative Need to develop a more quantitative assessment tool CASBEE-HI has been developed as a tool for detailed quantitative assessment on the performance of various countermeasures related to building design CASBEE-HI: Comprehensive Assessment System for Building Environmental Efficiency on Heat-Island Mitigation 33

34 Rating tools for building performance around the world (for buildings) (Murakami) CASBEE is the Japanese rating tool for building performance CASBEE-HI was developed based on the original CASBEE 34

35 Purpose of CASBEE&CASBEE-HI By disclosing the results of rating To Lead Architectural Market to Think Highly of Environmental-Conscious Buildings To Activate Additional Innovations on Environmental Techniques 35

36 Outline of the presentation 1. Impacts of Urban Heat Islands on Living Environment in Tokyo 2. Mechanism causing Urban Heat Islands and their Countermeasures 3. Implementation of Policies for Heat-Island Mitigation by Japanese Central Government 4. Implementation of Policies for Heat-Island Mitigation by Local Government of Tokyo 5. Suggestions by AIJ ( Architectural Institute of Japan) 36

37 Regulatory Requirement of Greening Roofs The Tokyo Metropolitan Government Ordinance was revised in April 2001 to include the regulatory requirement of green roofs. For new buildings with construction areas larger than 1000 m 2 (for public building; larger than 250 m 2 ), at least 20% of roof area, where people can access, is requested to install greening on the roof. 37

38 About 60 ha of green areas have already been created by this regulation. Total sq. meters = 58.9ha FY2001 FY2002 FY2003 FY2004 平成 13 年度平成 14 年度平成 15 年度平成 16 年度

39 However, there was strong opposition on this regulation. Many researchers claimed that such regulation is not appropriate as there are other countermeasures applicable to rooftop, such as high reflective paint. Reflected solar radiation: High reflective painting on the roof Reduced cooling load Now, Tokyo Metropolitan government has more comprehensive programs including not only greening but also other various measures. 39

40 TMG Master Plan for Environment Formulated in January 2002 Goal : to reduce the number of tropical nights to less than 20 per year in 2015 (from 31 tropical nights in 2005) The program includes: rooftop greening, high reflective paint, retentive water pavement, road surface watering, promoting urban ventilation, etc. 40

41 New Strategy - Thermal Environment Map - Major factors causing temperature increase are different in each region. So, appropriate measures should be selected according to the regional characteristics in each region. To help selecting the effective measures in each region, the Thermal Environment Map has been developed. 41

42 This map shows the distribution of contributing factors to the Heat Island Phenomenon, resulted from anthropogenic heat and the ground surface conditions of different districts. 17 factors related to Heat Island, such as a) anthropogenic heat releases from building facilities, automobiles, etc., b) ratios of surface areas covered with lawns, trees, asphalt, etc. c) averaged building heights, floor area ratios, sky view-factors, etc. d) ratios of office, residence, etc. 42

43 Thermal Environment Map in Tokyo Type I Business Center I-1 large heat loads from ground and large anthropogenic heat I-2 large heat loads from ground I-3 large anthropogenic heat relatively low heat load compared to other areas in business center Type II Residential Area II-1 large heat loads from ground in daytime II-2 large heat loads from ground throughout whole day II-3 relatively low heat load compared to other residential areas III Type III ( relatively large portion of natural land-use ) IV Type IV ( open area ) V Type V ( mixed area ) 43

44 Measures appropriate for each category Category Greening on the ground Greening on the roof Greening on the wall high reflective paint on the roof Water retentive pavement Reduction of anthropogeni c heat I-1 I-2 not effective I-3 II-1 not effective not effective II-2 not effective 44

45 Measures appropriate for each category Category Greening on the ground Greening on the roof Greening on the wall high reflective paint on the roof Water retentive pavement Reduction of anthropogeni c heat I-1 ( not ) I-2 not effective I-3 II-1 II-2 not so not many open spaces on not effective effective Category I-1: Business center. the ground. not effective 45

46 Measures appropriate for each category Category Greening on the ground Greening on the roof Greening on the wall high reflective paint on the roof Water retentive pavement Reduction of anthropogenic heat I-1 Category II-1 & II-2: Residential areas. I-2 Anthropogenic heat release is not I-3 II-1 II-2 not effective not effective so large compared to business center. not effective not effective 46

47 Outline of the presentation 1. Impacts of Urban Heat Islands on Living Environment in Tokyo 2. Mechanism causing Urban Heat Islands and their Countermeasures 3. Implementation of Policies for Heat-Island Mitigation by Japanese Central Government 4. Implementation of Policies for Heat-Island Mitigation by Local Government of Tokyo 5. Suggestions by AIJ ( Architectural Institute of Japan) 47

48 The Proposal from the Architectural Institute of Japan ( AIJ ) for Urban Heat Island Reduction Strategies was issued in July 2005 ( cf. section 5 in our report ). During the process of making this proposal, there were active discussion about urban greening, high reflective paints and materials. 48

49 Effects of tree canopy on outdoor thermal environment + :effects that improve the thermal comfort in summer - :effects that increase the discomfort in summer 4 Generation of vapor 1Shading effects on radiation :+ 2Decrease of reflected heat : + 3Decrease of wind velocity :- 4Generation of vapor 1) Decrease of air temperature:+ 2) Increase of air humidity :- 3 Total Effects? (+or -?)

50 Problems with greening (1) 1) Greening can surely decrease air temperature but it increases air humidity and decreases wind velocity. ->Are the increase of air humidity and the decrease of wind velocity acceptable in cities located in hot and humid climate in Asian countries? Densely planted trees sometimes cause problems. Careful planning of tree shape, density and arrangement is recommended in terms of shading effects, wind conditions etc. 50

51 Problems with greening (2): costs Reflective paint on the roof 4,500 5,000 Yen / m 2 ( HK$ / m 2 ) ( US$ / m 2 ) Greening on the roof ( light soil + lawn type ) 15,000 20,000 Yen / m 2 ( 1,000 1,350 HK$ / m 2 ) ( US$ / m 2 ) Roof Garden with planted trees -> more than 50,000 Yen / m 2 51

52 Problem with reflective materials Reflective paints and materials increase the reflection of solar radiation. If they are applied to areas where many people access, the increased reflected solar radiation hits the human body and heat stress of the human body is increased. 小さな熱負荷 52

53 Consensus at Present Stage 1)Well designed greening has various good impacts on living environment in urban space, not only for the improvement of thermal environment but also the improvement of landscape ( beautiful scenery ), ecosystem and good impact on human mind ( healing effects ), etc. 2)So, it should be intended to promote high quality urban greening to improve the quality of living environment in urban space. 3)Low quality greening with low cost that will not contribute to beautiful landscape should be avoided. 53

54 High quality greening can contribute to the improvement of urban space amenity Economical greening If such greening is misused, high reflective painting would be more effective in terms of cost/benefit. 54

55 Fundamental Point of View in the AIJ Proposal 1)Heat island countermeasures greatly affects various elements within society such as landscape ( scenery ), ecosystem, etc. 2)If we only focus on the effectiveness of heat island mitigation, the amenity of outdoor living space may not necessarily be improved. 3)So, it is important to enforce comprehensive planning from the viewpoint of human living. 4)Especially, for greening as a common topic in Japan and Hong Kong, it is important to promote high quality greening that will contribute to the improvement of urban space amenity. 55