City Speak X: A Green City, A Cool City Speaker: Edward Ng Yan-yung Urban heat and air ventilation – what are the implications for public health? Hong Kong is surrounded by so much water and has so many green mountains, so does it really need more urban open space? How do we respond to the threats of global warming and air pollution? What is the meaning of “the urban heat island effect”? What is an “air ventilation assessment”? What value doesthe community place on open space? Is the demand for recreation and sport changing? Do we need a landscape vision and master plan? Is “green infrastructure” becoming more important than roads and railway lines in securing a sustainable built environment in Hong Kong? Join experts, academics, planners, government officials and landscape architects in a discussion about how to stay cool in our city. Designing Hong Kong is a not-for-profit organisation focused on sustainable urban planning. See: www.designinghongkong.com

1. Green space, what for?
Professor Edward Ng
3 March 2010

2. Background
3 March 2010

3. Background
Global warming and urban heat island
3 March 2010

4. Background
Courtesy Professor Janet Nicole of PolyU
3 March 2010

5. Background
France's largest undertaker service says 15,000 died in August heat wave
3 March 2010

6. Background
This city is heading towards a hot, stuffy state of atmosphere. In future
summers, the old and the weak living in their tiny rooms in the urban areas will have to
face the increasing number of hot nights with no air-conditioning, little wind and the
dampness arising from little sun and little evaporation. They also have to fear the attack
of more germs than used to be since their natural enemies, viz. fresh air and sunshine,
have been reduced in strength.
Unfortunately the underprivileged have to look forward to even more tall
buildings along the shore or even right at the heart of the urban areas to block the little
wind and sunshine left.
CY Lam, ex-Director of HKO
3 March 2010

7. Due to Climate change
and global warming,
couple that with more
intense UHI, heat stress,
heat wave and heat spell
will be more frequent,
more intensive and will
last longer.
The elderly are particularly at risk
3 March 2010

8. Examples and References
What influences Urban Climate? Urban Boundary Layer
Time
• day
• season
Weather
City location • wind
• climate • Cloud
• topography • Temperature Urban Canopy Layer
• rural surrounds • RH Roughness sub-layer
Urban • Radiation
City metabolism Climate
• energy/water use Modified after Oke (1997)
• waste & emissions
City form
• material & fabric
• structure
• building cover
City size Every city is different, for sub-
• size tropical climate, optimising the
• density of land uses Oke, 1980, unpubl. city for human thermal comfort
‘Fixed’ – Location
in the summer months and
providing air ventilation are
‘Modulators’ – Time, Weather
essential considerations for
‘Manageable’ (policy, planning, design) – Size, Form, Metabolism planners
3 March 2010

9. Examples and References
Different Levels of Urban Climatic Planning Actions
Objectives Strategies Planning Actions Planning Time Scale Spatial Scale
• Cool material-building &
Immediate
pavement; city Effect
Albedo Material & Surface
• Cool roof & facade;
• Water retention paving; Level Intervention
UHI • Planting & greeneries;
Thermal Vegetation
• Parks & open spaces;
Comfort
• Building geometric design;
• Shelter design;
Building Level
+ Shading • Street orientation;
Intervention
• H/W ratio;
Wind • Trees;
Dynamic • Air paths;
Potential • Building ground cover
& building bulks;
Ventilation • H/W ratio; Urban & Planning
• Street orientation; Level Intervention Local Effect
• Open spaces; Long term (neighbourhood
• Building disposition; scale)
3 March 2010

10. Examples and References
What is Urban Climatic Map?
Urban Climatic Map integrates urban climatic factors and town planning considerations. It
provides a spatial information platform to planners for making informed environmental /
planning decisions.
It has 2 components
• The Urban Climatic Analysis Map
• The Urban Climatic Planning Recommendation Map
Berlin UC-Maps 1988-1992
3 March 2010

11. Examples and References
UCMap Studies in Stuttgart, Germany (late 1980s - )
Urban Climatic Analysis Map Urban Climatic Recommendation Map
Climatic Analysis Map Recommendation Map for Urban Planning
VDI 3787 Part 1: Environmental Meteorology, Climate and Air Pollution Maps for Cities and Regions
Key Lessons Learnt:
Heat and Wind for Human Comfort; The use of “Climatopes” and Urban Climatic
Planning Classes; Generic Planning recommendations
3 March 2010

12. Examples and References
3 March 2010

13. Examples and References
UCMap Studies in Tokyo, Japan (2000 - )
Key Lessons Learnt:
Greening; Sea Breezes & Mountain
winds; air paths; building volume and
coverage; anthropogenic heat
3 March 2010

14. The draft HK Urban Climatic Analysis Map
The concept of ( ) 度
Physiological Equivalent Temperature (PET)
as the synergizing variable for the HK Urban Climatic Analysis Map
Humidity, solar radiation and Survey on Thermal
other physiological factors Sensations
PHYSIOLOGICAL
EQUIVALENT
AIR AIR
VENTILATION TEMPERATURE TEMPERATURE
Dynamic potentials PET Thermal load
*note*
Human Thermal Comfort evaluated Physiological Equivalent Temperature
(PET) is the temperature of a reference
environment based on a heat balance
model that combines various climatic and
physiological variables including air
temperature, relative humidity, solar
radiation, air movement, clothing and
metabolic rate to give a synergetic
indication of human thermal comfort. It is
an index widely used to understand the
Urban Climatic Analysis Map (PET) thermal comfort environment
3 March 2010

15. The draft HK Urban Climatic Analysis Map
Technical input to HK UC-AnMap
User urban thermal comfort survey
Field measurements
Wind tunnel studies
Computational Fluid Dynamics (CFD) studies
Wind (MM5 / CALMET) studies
Wind Tunnel Study Thermal Comfort Study CFD Study
3 March 2010

16. The draft HK Urban Climatic Analysis Map
Layer structure of UC-AnMap
Buildings Landuse Topography
Building Volume Topography Green Space Ground Coverage Natural Landscape Proximity to Openness
+
Thermal Load Dynamic Potential
Draft UC-AnMap Further Wind Information Final UC-AnMap
+ =
3 March 2010

17. The draft HK Urban Climatic Analysis Map
3 March 2010

18. The draft HK Urban Climatic Analysis Map (UC-AnMap)
3 March 2010

19. The draft HK Urban Climatic Planning Recommendation Map
Building setback & permeability, Air paths, Open spaces (air ventilation connectivity) +
greenery
3 March 2010

20. The draft HK Urban Climatic Planning Recommendation Map
Green Spaces:
Ground (site) Coverage:
Water – sea breezes
Proximity to Openness + connectivity:
Vegetated hill slopes
3 March 2010

21. The draft HK Urban Climatic Analysis Map (UC-AnMap)
Urban climatically
Open spaces increase urban porosity and air
volume at the pedestrian level, thus allowing
better urban ventilation penetration. Linkage
of open spaces allows better connectivity
and improves air mass exchange.
Furthermore
Greening lower the urban mean radiant
temperature, increase trans-evaporation and
hence improve urban human thermal comfort.
Tree canopy also provide shading.
3 March 2010

22. So, … happy “spacing” and “greening”, …
Thank you
5 , “ ”
A sketch by a 5 years old, titled “my Hong Kong”.
3 March 2010