simulating climate change in urban areas: interactions ... · overview model formulation &...
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1 00/XXXX © Crown copyrightHadleyCentre
Simulating climate change in urban areas: interactions between greenhouse forcing, land
surface effects and heat sources
Richard Betts
Martin Best
2nd BETWIXT workshop, Birmingham University, 13-14 May 2004
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2 00/XXXX © Crown copyrightHadleyCentre
Alternative title:
What is wrong with what we gave to UKCIP02?
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HadleyCentre
Urban heat islands
� Cities can be several °C warmer than surrounding rural areas
� Several reasons for this, including:
– character of the land surface
» concrete/tarmac surface instead of vegetation (less soil water infiltration and evaporation)
» heat capacity of buildings
– sources of heat within the urban area
� Studies of climate change impacts in urban areas must take this into account
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HadleyCentre
Greenhouse effect
Fossil fuel burning
Climate change
Local climate change
Impacts
Fossil fuel burning, climate change and its impacts
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HadleyCentre
Greenhouse effect
Fossil fuel burning
Climate change
Local climate change
Impacts
Fossil fuel burning, climate change and its impacts
GCMs/RCMs
Downscaling
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HadleyCentre
Greenhouse effect
Fossil fuel burning
Climate change
Local climate change
Impacts
Fossil fuel burning, climate change and its impacts
Land-atmosphere feedbacks
GCMs/RCMs
Downscaling
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HadleyCentre
Greenhouse effect
Fossil fuel burning
Climate change
Local climate change
Impacts
Fossil fuel burning, climate change and its impacts
Land-atmosphere feedbacks
Direct heating
GCMs/RCMs
Downscaling
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HadleyCentre
Greenhouse effect
Fossil fuel burning
Climate change
Local climate change
Impacts
Fossil fuel burning, climate change and its impacts
Land-atmosphere feedbacks
Direct heating
GCMs/RCMs
Downscaling
![Page 9: Simulating climate change in urban areas: interactions ... · Overview Model formulation & experimental design Heat island due to land surface effects – current climate – doubled-CO2](https://reader033.vdocuments.net/reader033/viewer/2022050520/5fa38c71410b851b6244d1d3/html5/thumbnails/9.jpg)
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Overview
� Model formulation & experimental design
� Heat island due to land surface effects– current climate
– doubled-CO2 climate
� Effect of land-atmosphere feedbacks on changes in heat island under doubling CO2
– can we assume heat islands remain unchanged?
� Effect of direct heat sources on heat island– comparison with doubled-CO2 warming
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Representations of sub-gridscaleland surface
heterogeneityT
H
T3
T2
T1
T4
H1 H2 H3 H4
“Effective parameters” (HadCM3 / AM3 / RM3, used in UKCIP02)
“Tiles” (HadCM3-MOSES2
& new model HadGEM1)
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Urban areas and anthropogenic heat source in model surface energy budget
S+tT
C∂∂
K↓K↑
L↓L ↑H λES
L*
Hs
Ls
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Experimental Design
N1N None1xNo
U1N None1xYes
N2N None2xNo
U2N None2xYes
U1C Current1xYes
U2C Current2xYes
U2F Future2xYes
ID Heat SourceCO2Urban
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Fraction of GCM gridbox specified as urban land
Horizontal resolution: 2.75° × 3.75°
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Comparing climate change in urban and non-urban areas
(no additional heat sources)
� 1×CO2 simulation with urban areas– compare temperature on urban and non-urban tiles
� 2×CO2 simulation with urban areas– compare temperature on urban and non-urban tiles
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Simulated present-day distributions of daily maximum and minimum temperatures: London gridbox
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Simulated distributions of daily maximum and minimum temperatures under doubled CO2: London gridbox
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Do we need to model the urban heat islands, or can we just add on present-day climate patterns
to standard modelled climate change?
� Extract urban heat island from present-day simulation
� Simulate doubled-CO2 climate change without urban areas included
� Add on present-day urban heat island
� Compare urban temperatures with those simulated in 2×CO2 run including urban areas
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Effect of feedbacks on urban temperatures under doubled CO2
“Prognostic” (red): urban temperatures simulated within GCM
“Diagnostic” (black): doubled-CO2 climate + present-day heat island
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How important are direct heat sources for urban climate change?
� Consider 3 cases:
� No direct heat source
� Estimated present-day heat source
� Extrapolated heat source for time of doubling of CO2
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Determining the Heat Source
World Resources Institute www.wri.org/trends/emission2.html
1 Tonne of Oil Equivalent = 41.868 GJ
Global Energy Use ≈ 335 EJ (1018)
Distributed Globally = 0.02 Wm-2
Distributed Over Land = 0.06 Wm-2
(Land = 35% of Globe)
Distributed Over Cities = 45.8 Wm-2
(Cities = 0.046% of Globe= 0.14% of Land)
Future AnthropogenicHeat Source = 60 Wm-2
Current Day AnthropogenicHeat Source = 20 Wm-2
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Impact of direct anthropogenic heat source on simulated doubled-CO2 temperatures
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Relative impact of heat source and doubling CO2 on urban temperatures
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U1C
U2C
U2F
Relative impact of heat source and doubling CO2 on urban heat island (urban - grass temperatures)
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Conclusions
� Urban land warmer than non-urban land both at present-day and under doubled CO2
� Even with no change in heat source, character of urban heat island changes under doubling CO2
due to land-atmosphere feedbacks
� Tripling of heat source source significantly changes character of urban heat island
� Tripling heat source has smaller impact than doubling CO2 concentration, but still significant
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Impact of Heat Source
U2NU2CU2F
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Including Urban Areas
‘Diagnostic’
U2F
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Relative Impact of Local Source
U1CU2CU2F