Evolution and future projections of the urban heat island at the coastalurban area of Athens
D. Founda1, C. Giannakopoulos1, M. Hatzaki1, M. McCarthy2,C. Goodess3, D. Hemming2, and F. Pierros1
1Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Greece2Met Office Hadley Centre, UK3Climatic Research Unit, School of Environmental Sciences, University of East Anglia, UK
• Athens is a large urban area of eastern Mediterranean that experiences both global warming and urbanization effects
• According to the historical records of the National Observatory of Athens (NOA), the annual air temperature in Athens reveals a statistically significant positive trend from the beginning of the past century till now
• This is due to the increase of the summer rather than the winter temperature• The increase of the maximum temperature in summer during the last few
decades (since the mid 1970’s) is significantly large and amounts roughly to 1°C/decade
• Summer 2007 was an exceptionally hot summer in Athens, with three severe heat waves and an all time record value in the maximum temperature (44.8°C at NOA)( Founda & Giannakopoulos 2009)
• However, summer 2012 (June – August) was the warmest summer ever recorded at NOA as regards the mean maximum and minimum air temperature
Air temperature trends in Athens
y = 0.02x - 4.61
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25
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1890 1910 1930 1950 1970 1990 2010
year
Air t
empe
ratu
re (C
)Mean summer temperature at NOA (1897-2010)
Trends 1897-2010: + 0.16°C/decade, or ~ 1.8°C
Trends 1976-2010: +0.9°C/decade, or ~ 3°C
Mean winter temperature at NOA (1897-2010)
Trends 1897-2010: +0.02°C/decade, or ~ 0.22°C
Trends 1976-2010: +0.15°C/decade, or ~ 0.5°C
y = 0.0024x + 5.3508
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1890 1910 1930 1950 1970 1990 2010
year
Air t
empe
ratu
re
global climate responds to the radiative forcing and feedbacks resulting from emissions of greenhouse gasesregional climates further respond to drivers as land-use change, agriculture, deforestation, and irrigationlocalised micro-climates can develop as a result of immediate human activity and settlements
most apparent and widely known expression of this is the urban heat island (UHI) effect: measurably warmer urban areas than surrounding rural environments
UHI intensity: reflected by temperature differences between urban and rural sites depends on the size, population and industrial development of a city, topography, regional climate and meteorological conditions
Global warming or urbanization?
should be considered on three different scales
First, there is the mesoscale of the whole city
Second is the local scale on the order of the size of a park
Third scale is the microscale of the garden and buildings near the meteorological observing site
Of the three scales the microscale and local-scale effects generally are larger than mesoscale effects
Urban heat island
UHI in Athens is of the order of 4-5°C between urban and suburban stations (Livada et al. 2005)
But UHI can be of the order of 10°C between rural stations and the central zone of the city
Significant research on spatial variability of UHI in Athens, but…
• Studies concerning the rates of changes of UHI over time are missing
• It is important to know whether the intensity of the urban heat island in the city continues to amplify, if it has moderated or has stabilized
Urban heat island in Athens – previous research
Helliniko (HEL) ► urban coastal
Tatoi (TAT) ► rural – suburban
Tanagra (TAN) ► rural (airport)
Aliartos (ALI) r► ural
Elefsis (ELE) ► suburban (industrial)
Selected Stations
NOA represents the ‘background’ urban conditions in Athens on the mesoscale
NOA urban in a park ► (unchanged environment local and microscale)
y = 0.09x - 150.12
y = 0.10x - 168.62
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34
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37
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
HEL maxNOA max
Summer maximum temperature
Similar trends at NOA and HEL
NOA (urban) and HEL (coastal urban) stations
Summer average temperature
222324252627282930
1975 1980 1985 1990 1995 2000 2005
rural1rural2urban1urban2
Summer maximum and minimum tempearure
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1975 1980 1985 1990 1995 2000 2005
rural1(max) rural1(min) rural2(max) rural2(min)urban1(max) urban1(min) urban2(max) urban2(min)
Summer average, maximum and minimum temperatures at two urban and two rural stations
y = 0.04x - 79.43
y = 0.04x - 79.99
-0.8
-0.4
0
0.4
0.8
1.2
1.6
1975 1980 1985 1990 1995 2000 2005
NOA-TAN (avg)HEL-TAN(avg)
y = 0.02x - 41.93
y = 0.02x - 41.38
-0.5
0
0.5
1
1.5
2
2.5
1975 1980 1985 1990 1995 2000 2005
HEL-TAT(avg)NOA-TAT(avg)
UHI (Turban –Trural)
UHI (Turban – Tsuburban)
Summer UHI Temporal Variation and Trends
y = -0.0008x + 11.586
y = -0.0005x + 11.589
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1975 1980 1985 1990 1995 2000 2005
win
ter t
empe
ratu
re (C
)
HEL avg
NOA avg
Winter temperature at NOA (urban) and HEL (coastal urban) stations
Similar trends (no statistical significant trend)
UHI (Turban –Trural)
y = 0.02x - 37.87
y = 0.02x - 37.87
0
1
2
3
4
1975 1980 1985 1990 1995 2000 2005
NOA-TAN avgHEL-TAN avg
y = 0.01x - 17.95
y = 0.01x - 17.95
0
1
2
3
4
1975 1980 1985 1990 1995 2000 2005
HEL-TAT avgNOA-TAT avg
Winter UHI TrendsUHI (Turban –Trural)
UHI (Turban – Tsuburban)
Summer average air temperature trends after 1976 at two urban stations in Athens are of the order of 1°C/decade
UHI in summer increases at a rate of the order of 0.4°C /decade (urban-rural) or 0.2°C/decade (urban-suburban)
Roughly 60% of warming is due to global warming and the rest 40% is due to urban effect
Winter average air temperature after 1976 at two urban stations in Athens reveal no significant trend. UHI in winter, increases at a rate of the order of 0.2°C/decade (urban-rural) or 0.1oC/decade (urban-suburban).
Results on Athens UHI temporal evolution
Model simulationsA novel climate model that includes a sub-grid urban land-surface model was applied for an integrated impacts assessment for the Athens urban case study
► in order to quantify the cumulative impact and relative importance of
climate change and urban heat island
to the exposure of urban populations to temperature extremes as it is essential to consider the combined role of global warming and local urban warming
T3
T2T1
T4
H1 H2 H3 H4
Urban Heat Island SimulationsHadRM3 modified to include MOSES 2.2 land-surface scheme and urban parameterisation ►“tiled” surfaceThe "tiles" allow sub-grid variationsNine extracted gridcells over and surrounding the tree cities
1971-1990 2041-2060
NoUrbNoAnth -
UrbNoAnth UrbNoAnthUrbAnth UrbAnth
- Urb3Anth
Urban fraction is set to zero
Fully coupled urban modelFully coupled
urban model including additional anthropogenic term
As UrbAnth, but with tripled anthropogenic heat flux
Surface tile scheme, representing land surface exchanges within a single model gridcell
Urban Heat Island Simulations – gridcells
Gridcells organised as:1 2 3 4 5 6 7 8 9
cell 5 represents the city centre location and 1,2,3,4,6,7,8,9 are surrounding
22 .5 23 23 .5 24 24 .5 2537 .5
38
38 .5
39
1 2 34 5 6
7 8 9
Climate model bias
• Larger RMSE for coastal points than for neighboring inland points, suggesting coastal influence on the apparent model bias
Urban Tile Temperatures - AthensTmin
0
5
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25
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0 2 4 6 8 10 12
NoUNoA
UNoA
UA
NOA
Tmax
0
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30
35
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0 2 4 6 8 10 12
NoUNoA
UNoA
UA
NOA
Tmin
-5
-4
-3
-2
-1
0
1
2
0 2 4 6 8 10 12
NoUNoA
UNoA
UA
Tmax
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10 12
NoUNoA
UNoA
UA
Intra-annual cycle of Tmin and Tmax (upper panels) for NoUrbNoAnth, UrbNoAnth, UrbAnth simulations and observations and the differences (lower panels) between simulations and observations, using urban tile temperatures, between 1971-1990.
RMSE1.501.541.49
RMSE2.442.091.74
Gridcell mean temperatures - Athens
Intra-annual cycle of Tmin and Tmax (upper panels) for NoUrbNoAnth, UrbNoAnth, UrbAnth simulations and observations and the differences (lower panels) between simulations and observations, using gridcell mean temperatures, between 1971-1990.
-6.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
0 2 4 6 8 10 12
NoUrbNoAnth
UrbNoAnth
UrbAnth-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
0 2 4 6 8 10 12
NoUrbNoAnth
UrbNoAnth
UrbAnth
Tmin
0.00
5.00
10.00
15.00
20.00
25.00
0 2 4 6 8 10 12
NoUrbNoAnth
UrbNoAnth
UrbAnth
NOA
Tmax
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0 2 4 6 8 10 12
NoUrbNoAnth
UrbNoAnth
UrbAnth
NOA
RMSE1.481.511.39
RMSE4.342.742.42
RMSE1.481.511.39
RMSE4.342.742.42
Urban model bias – Athens case
greatest impact of anthropogenic waste heat on the UHI during winter
during summer, it becomes a small term relative to the solar forcing
gridcell-5
0
0.5
1
1.5
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2.5
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0 2 4 6 8 10 12
UrbAnth-NoUrbNoAnth
UrbNoAnth-NoUrbNoAthn
Model evaluation
22 .5 23 23 .5 24 24 .5 2537 .5
38
38 .5
39
1 2 34 5 6
7 8 9
Summer Daytime/Nocturnal UHI UHIurban-ruralobs NoUrbNoAnth RMSE
daytime 0.16 1.14 0.98nocturnal 4.55 2.72 1.83
obs UrbNoAnth RMSEdaytime 0.16 1.06 0.9
nocturnal 4.55 4.57 0.02obs UrbAnth RMSE
daytime 0.16 1.07 0.91nocturnal 4.55 4.75 0.2
UHIurban-ruralobs NoUrbNoAnth RMSE
daytime 0.55 0.71 0.16nocturnal 4.39 2.00 2.39
obs UrbNoAnth RMSEdaytime 0.55 0.71 0.16
nocturnal 4.39 3.93 0.46obs UrbAnth RMSE
daytime 0.55 0.77 0.22nocturnal 4.39 4.11 0.28
UHIurban-suburban
obs NoUrbNoAnth RMSEdaytime 0.59 1.07 0.48
nocturnal 3.77 0.45 3.32obs UrbNoAnth RMSE
daytime 0.59 1.16 0.57nocturnal 3.77 2.21 1.56
obs UrbAnth RMSEdaytime 0.59 1.13 0.54
nocturnal 3.77 2.39 1.38
Winter Daytime/Nocturnal UHI UHIurban-rural
UHIurban-rural
UHIurban-suburban
obs NoUrbNoAnth RMSEdaytime 1.50 1.38 0.12
nocturnal 3.50 -0.07 3.57obs UrbNoAnth RMSE
daytime 1.50 1.44 0.06nocturnal 3.50 1.69 1.81
obs UrbAnth RMSEdaytime 1.50 1.51 0.01
nocturnal 3.50 1.99 1.51
obs NoUrbNoAnth RMSEdaytime 1.20 0.77 0.43
nocturnal 3.40 -1.09 4.49obs UrbNoAnth RMSE
daytime 1.20 0.81 0.39nocturnal 3.40 0.68 2.72
obs UrbAnth RMSEdaytime 1.20 0.87 0.33
nocturnal 3.40 1.04 2.36
obs NoUrbNoAnth RMSEdaytime 1.40 0.38 1.02
nocturnal 3.00 0.67 2.33obs UrbNoAnth RMSE
daytime 1.40 0.45 0.95nocturnal 3.00 1.94 1.06
obs UrbAnth RMSEdaytime 1.40 0.5 0.90
nocturnal 3.00 2.13 0.87
Future Projections of UHI for summerUHIurban-rural
UHIurban-rural
UHIurban-suburban
UrbNoAnth %daytime 0.97 -8.5
nocturnal 4.67 2.2UrbAnth
daytime 1.05 -1.9nocturnal 4.66 -1.9
Urb3Anthdaytime 1.12 4.7
nocturnal 5.16 11.0
UrbNoAnth %daytime 0.83 16.9
nocturnal 4.40 12.0UrbAnth
daytime 0.75 -2.6nocturnal 4.18 1.7
Urb3Anthdaytime 0.86 16.2
nocturnal 4.69 16.7
UrbNoAnth %daytime 1.14 -1.7
nocturnal 2.17 -1.8UrbAnth
daytime 1.17 3.5nocturnal 2.29 -4.2
Urb3Anthdaytime 1.27 11.4
nocturnal 2.72 18.3
Future Projections of UHI for winterUHIurban-rural
UHIurban-rural
UHIurban-suburban
UrbNoAnth %daytime 0.97 -8.5
nocturnal 4.67 2.2UrbAnth
daytime 1.05 -1.9nocturnal 4.66 -1.9
Urb3Anthdaytime 1.12 4.7
nocturnal 5.16 11.0
UrbNoAnth %daytime 1.09 34.6
nocturnal 1.26 85.3UrbAnth
daytime 0.88 1.1nocturnal 0.95 -8.7
Urb3Anthdaytime 1.06 26.2
nocturnal 1.52 90.0
UrbNoAnth %daytime 0.41 -8.9
nocturnal 1.99 2.6UrbAnth
daytime 0.52 4.0nocturnal 2.15 0.9
Urb3Anthdaytime 0.65 38.3
nocturnal 2.46 21.8
Model Results
The analysis of the influence of the urban land surface and urban anthropogenic heat emissions for Athens showed that:the main characteristics of a Mediterranean UHI captured by a simple urban surface exchange scheme, when compared observational data for Athenstemperature changes in response to an SRES A1B scenario by the 2050s are similar for urban and nonurban surfaces future climate change will affect the urban and rural areas as wellfuture UHI responds to changes in the additional driver of anthropogenic heat emissions of a city
Thank you for your attention!
The model simulations were performed within the context of EU-FP6 project CIRCE Integrated Project-Climate Change and Impact Research: the Mediterranean Environment (http://www.circeproject.eu).
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