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 - anazelle@imperial.ac.uk

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)