Climate Change, Cities, and
the Urban Heat Island
Mark McCarthy, Martin Best, Richard Betts, Maggie Hendry
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Contents
This presentation covers the following areas
• Human exposure to climate stress.
• A simple coupled urban-climate model.
• Energy use and the urban environment.
• Cities in a regional climate model.
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Majority of population
residing within urban areas
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Figure from the UN department of Economic and Social Affairs
Human Exposure to climate
stress
• Population dynamics and
urbanisation will
contribute to future
exposure of humans to
climate stress.
• Can we design climate
models that are useful
impacts and adaptation tools
despite uncertainties?
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A simple urban climate
model
•Mark McCarthy
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A simple urban scheme for a
climate model
Atmosphere
SW
H
LE
LW
C(dT/dt)+G=Rn-H-LE-Qf
Ground
Best et al. 2006: Boundary layer Meteorology 118: 503-525
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Subgrid heterogeneity
H1
•Urban parameters:
H2
H3
H4
•Albedo
•Roughness length of
heat and momentum
T2
T1
•Heat Capacity
•Anthropogenic heat
release
T3
T4
•Impervious surface
Essery et al. 2003: J. Hydrometeorology, 4, pp.530-543
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Urban Heat Island responds to
climate feedbacks but not
forcings in a 2XCO2 experiment
Diurnal Temperature Range
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Energy use
•Mark McCarthy
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Energy use and urban heat
islands.
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Energy use data courtesy of London
Energy and CO2 inventory 2003
Global mean change
Change in average
temp.
2*CO2 + UHI + 60Wm-2
2*CO2 + UHI + 20Wm-2
2*CO2 + UHI
2*CO2
Global mean change
Change in 95th %ile
temp.
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Energy use and climate.
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Load data courtesy of EDF energy
Energy use-climate-urban
feedbacks
• Urban climates can change in
response to climate change.
• Urban climates can change in
response to local
anthropogenic forcing.
• Local anthropogenic forcing
can change in response to
climate.
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Cities in a regional climate
model
•Mark McCarthy
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Urban heat islands in HadRM3
– offline ‘v’ coupled
Model
Obs
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London Weather Centre
St James Park
Heathrow
Northolt
2oC
Seasonality and magnitude of a
heat island simulated by RCM
LWC – Wisley
Observations
SJP – Wisley
Observations
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HadRM3 London
Anthropogenic heating and
extremes.
• Avg annual no. of hot nights (>20oC):
• Present day Climate:
• No urban = 0.45
• Coupled urban = 2.9
• Coupled urban + 25Wm-2 = 4.2
• Coupled urban + 75Wm-2 = 4.4
• With 2.5oC Climate Change:
• No urban = 3.5
• Coupled urban = 14.6
• Coupled urban + 25Wm-2 = 16
• Coupled urban + 75Wm-2 = 22
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Summary.
• Forcings and feedbacks between
climate, local heat release, and the
urban heat island require coupled
climate-urban models.
• Met Office UM provides one such
framework.
• Simple scheme captures UHI.
• Warming similar for vegetation and
urban surface in HadCM3
• Local heating is significant additional
driver of change
• Feedbacks are important in 25km
regional model
• Important for capturing extremes in night
time temperatures.
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Objectives.
• Improved quantification of urbanisation and anthropogenic heating in
climate change.
• Urban model development, assessment and uncertainty (Maggie
Hendry – 9am Weds)
• Collaborations to develop urban planning tools and impact
assessments:
• SCORCHIO (SCORCHIO - Sustainable Cities: Options for Responding to
Climate cHange Impacts and Outcomes.
http://www.sed.manchester.ac.uk/research/cure/research/scorchio/
• CIRCE – Climate Change and Impacts research: The Mediterranean
environment
http://www.circeproject.eu/
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