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Greening cities and urban density Environmental and health impacts
Dr Audrey de Nazelle
CIBSE
Overcoming obstacles to high density resilient cities
London, January 6th 2017
Urban sanitary movement mid-19th century
- Miasma theories - epidemics disease outbreak caused by filth and foul
air
- Frederick Law Olmsted, John H Rauch, , Ildefons Cerdà, Edwin
Chadwick, Baron Haussmann
Planning focussed on the need for:
• sunlight, ventilation, greenery, waste disposal including good drainage
systems (sewers)
o Urban air pollution (9th highest risk factor for global burden of disease, Lim et al. 2012)
o The gobal physical inactivity pandemic (10th risk factor for global burden of disease, Lim et al. 2012)
o Climate change
o Traffic injuries (8th cause of death worldwide)
Sprawl: • increased obesity, overweight, BMI, hypertension, chronic diseases, traffic fatalities (Ewing et
al 2003, Lopez 2004, Sturm and Cohen 2004)
Neighborhood land use density, land use mix, “walkability”: • Positive effects on overweight, obesity, BMI, physical activity and mental health ( Giles-Corti
et al. 2003, Saelens 2003, Frank et al. 2004, Frank et al. 2007, Berke et al. 2007)
“Greeness” • Positive effects on stress recovery, emotions, physical activity, overweight, all-cause and
CVD-related mortality, mental health and wellbeing (van den Bosch and Nieuwenhuijsen 2016)
Current major public health challenges
Credit: Stockxpert.
Empirical evidence on planning and health
Density
Key benefit of density:
- Enables sustainable and active forms of transport (walking,
cycling, public transport) (Cervero and Ewing 2010)
Potential trade-off:
- Exposure to air pollution…
Air pollution and street canyons
Air pollution exposure and urban density
Su et al. Environment International 78 (2015) 82-89
Density (x axis) vs Population exposed defined as living within 300m of highways and
50m of major roads (y axis)
However, add in the greenspace…
Cost-effectiveness of street tree planting to reduce particulate matter
McDonald et al., Planting Healthy Air, The Nature
Conservancy 2016
scenario PM2.5
concentration
% reduction
Deaths/year attributable to
Air
pollution
General
population
physical
activity
Traffic
mortality
Air pollution
travellers
20% in-city
car trip
reduction, all
replaced by
biking
0.32 -5 -33.73 0.08 0.57
Encourage modal shifts…
Rojas-Rueda et al. Environment International 49 (2012) 100-109
Changes in air pollution and deaths/year for transport scenarios in Barcelona
scenario physical
activity
Air
pollution
Traffic
mortality
TOTAL
increased
active
travel
-528 -21 +11 -538
lower
carbon
emission
vehicles
0 -17 0 -17
Co-benefits of climate change strategies
Woodcock et al. (2009) Comparison of GHG emission policy scenarios in London: death per million people
Woodcock et al. 2009 The Lancet , v3674, 9705: 1930-1943
And take a holistic approach…
Potential co-benefits of planning strategies…
Estimated preventable deaths under compliance with exposure
recommendations by exposure domain in Barcelona, Spain.
Mueller et al Urban and Transport Planning Related Exposures and Mortality: A Health Impact Assessment for Cities EHP June 2016
Conclusion
Strategies such as well designed urban densities can
have multiple co-benefits and these should be
considered together to help prioritize policies
Audrey de Nazelle - [email protected]
extras
London air quality strategies: impacts on air pollution mortality, physical activity, and CO2 emissions (£)
Technological solutions
Behavioural solutions (mode shifts)
James Sykes thesis (+ Marko Ristic-Smith thesis + Andrea Calderon PhD)
Lim et al. The Lancet 2012; 380:2224-2260 (DOI:10.1016/S0140-6736(12)61766-8)
Burden of disease attributable to 20 leading risk factors in 2010, expressed as a percentage of
global disability-adjusted life-years
London’s Mayor Air Quality Strategy 2010
80% contribution
from traffic sector
35% from tyre and brake wear
Emission sources in cities
scenario PM2.5
concentration
% reduction
Deaths/year attributable to
Air
pollution
General
population
physical
activity
Traffic
mortality
Air pollution
travellers
20% in-city
car trip
reduction, all
replaced by
biking
0.32 -5 -33.73 0.08 0.57
20% in-out
city car trip
reduction,
20% replaced
by biking
0.58 -9.06 -49.17 -0.71 0.64
Changes in air pollution and deaths/year for transport
scenarios in Barcelona
Rojas-Rueda et al. Environment International 49 (2012) 100-109
Health impact assessments (HIA)
• Main message so far from all
of 20 published studies:
Benefits of active travel in
terms of physical activity
outweigh adverse effects
associated with air pollution
and/or traffic injuries
Photo: Gil Garcetti
©
Mueller et al. 2015. Health impact assessment of active
transportation: A systematic review. Preventive medicine 76, 103-114.
- Current Altmetric score 942: best score over all articles ever published in Preventive Medicine
- In "the top 5% of all research outputs ever tracked by Altmetric”
PA: Non-linear dose-response PM: Linear dose-response
For a given level of air pollution, is there a tipping beyond which
additional physical activity does not bring additional benefits,
and a “break-even” point beyond which additional physical
activity brings greater risks?
Delhi, 153 µg/m3 of PM2.5
Cycling a risk after 45 min of cycling per day
(Safe up to 2 hours
per day)
(Tipping point reached at 7
hours per day)