Evolution and future projections of
the urban heat island at the coastal
urban 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, Greece
2Met Office Hadley Centre, UK
3Climatic Research Unit, School of Environmental Sciences, University of East
Anglia, UK
Air temperature trends in Athens
•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
Mean summer temperature at NOA (1897-2010)
30
y = 0.02x - 4.61
Air temperature (C)
29
28
27
26
25
24
1890
1910
1930
1950
1970
1990
year
Trends 1897-2010: + 0.16°C/decade, or ~ 1.8°C
Trends 1976-2010: +0.9°C/decade, or ~ 3°C
2010
Mean winter temperature at NOA (1897-2010)
13
Air temperature
12
11
10
9
8
7
y = 0.0024x + 5.3508
6
1890
1910
1930
1950
1970
year
Trends 1897-2010: +0.02°C/decade, or ~ 0.22°C
Trends 1976-2010: +0.15°C/decade, or ~ 0.5°C
1990
2010
Global warming or urbanization?
global
climate responds to the radiative forcing and feedbacks resulting from
emissions of greenhouse gases
regional
climates further respond to drivers as land-use change, agriculture,
deforestation, and irrigation
localised
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

Urban heat island
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 in Athens – previous research
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
Selected Stations
NOA ► urban in a park (unchanged environment local and microscale)
Helliniko (HEL) ► urban coastal
Tatoi (TAT) ► rural – suburban
Tanagra (TAN) ► rural (airport)
Aliartos (ALI) ► rural
Elefsis (ELE) ► suburban
(industrial)
NOA represents the ‘background’ urban conditions in Athens on the mesoscale
Summer maximum temperature
NOA (urban) and HEL (coastal urban) stations
37
HEL max
NOA max
36
35
y = 0.09x - 150.12
34
33
32
31
y = 0.10x - 168.62
30
29
28
1970
1975
1980
1985
1990
1995
Similar trends at NOA and HEL
2000
2005
2010
2015
Summer average, maximum and minimum temperatures at two urban and
two rural stations
30
Summer average temperature
29
28
27
26
25
rura l 1
rura l 2
24
urba n1
urba n2
23
22
1975
1980
40
1985
1990
1995
2000
2005
Summer maximum and minimum tempearure
35
30
25
20
15
10
1975
rural1(max)
urban1(max)
1980
rural1(min)
urban1(min)
1985
1990
rural2(max)
urban2(max)
1995
rural2(min)
urban2(min)
2000
2005
Summer UHI Temporal Variation and Trends
1.6
1.2
NOA-TAN (avg)
HEL-TAN(avg)
UHI (Turban –Trural)
y = 0.04x - 79.43
0.8
0.4
y = 0.04x - 79.99
0
-0.4
-0.8
1975
2.5
2
HEL-TAT(avg)
NOA-TAT(avg)
1980
1985
1990
UHI (Turban – Tsuburban)
1995
2000
y = 0.02x - 41.38
1.5
1
0.5
y = 0.02x - 41.93
0
-0.5
1975
1980
1985
1990
1995
2000
2005
2005
Winter temperature at NOA (urban) and HEL (coastal urban) stations
13
y = -0.0005x + 11.589
winter temperature (C)
12
11
10
9
y = -0.0008x + 11.586
8
7
HEL avg
NOA avg
6
1975
1980
1985
1990
1995
Similar trends (no statistical significant trend)
2000
2005
Winter UHI Trends
UHI (Turban –Trural)
4
3
NOA-TAN avg
HEL-TAN avg
y = 0.02x - 37.87
2
y = 0.02x - 37.87
1
0
1975
1980
UHI (Turban –Trural)
1985
1990
1995
2000
2005
UHI (Turban – Tsuburban)
4
y = 0.01x - 17.95
3
2
y = 0.01x - 17.95
1
HEL-TAT avg
NOA-TAT avg
0
1975
1980
1985
1990
1995
2000
2005
Results on Athens UHI temporal evolution
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).
Model simulations
A 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
Urban Heat Island Simulations
Urban fraction is set
HadRM3 modified to include
to zero
MOSES 2.2 land-surface scheme
and urban parameterisation ►
“tiled” surface
The "tiles" allow sub-grid variations
Nine extracted gridcells over and
Fully
coupled
surrounding the
tree
cities urban
1971-1990
2041-2060
NoUrbNoAnth
-
UrbNoAnth
UrbNoAnth
UrbAnth
UrbAnth
-
Urb3Anth
model
H
H
H
Fully coupled urban H
model including
T
additional
T
As
UrbAnth, but with
anthropogenic term
Surface tile scheme,
tripled anthropogenic
T
representing land surface
heat flux T
exchanges within a single
model gridcell
1
2
3
4
2
1
3
4
Urban Heat Island Simulations – gridcells
39
38.5
38
37.5
22.5
Gridcells organised as:
123
456
789
cell 5 represents the city centre
location and 1,2,3,4,6,7,8,9 are
surrounding
23
1
2
3
4
7
5
6
8
9
23.5
24
24.5
25
Climate model bias
•Larger RMSE for coastal
points than for neighboring
inland points, suggesting
coastal influence on the
apparent model bias
Urban Tile Temperatures - Athens
40
Tmin
30
NoUNoA
25
35
UNoA
UA
20
Tmax
NoUNoA
NOA
UNoA
30
UA
25
NOA
20
15
15
10
10
5
5
0
0
0
2
4
6
8
10
0
12
Tmin
2
2.5
2
1.5
0
2
4
6
8
10
12
8
10
12
Tmax
NoUNoA
UNoA
UA
0.5
0
-2
-0.5 0
-3
NoUNoA
-5
6
1
-1
-4
4
3
1
0
2
UNoA
UA
RMSE
2.44
2.09
1.74
2
4
6
8
10
12
-1
-1.5
-2
-2.5
RMSE
1.50
1.54
1.49
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.
Gridcell mean temperatures - Athens
25.00
NoUrbNoAnth
20.00
40.00
Tmin
NoUrbNoAnth
UrbNoAnth
35.00
UrbNoAnth
UrbAnth
30.00
UrbAnth
NOA
Tmax
NOA
25.00
15.00
20.00
10.00
15.00
10.00
5.00
5.00
0.00
3.00
0.00
0
2
4
6
8
10
12
4.00
2.00
0
2
4
6
8
10
12
0
2
4
6
8
10
12
3.00
1.00
2.00
0.00
-1.00
0
2
4
6
8
10
12
1.00
-2.00
0.00
-3.00
-4.00
NoUrbNoAnth
-5.00
UrbNoAnth
-6.00
UrbAnth
RMSE
4.34
2.74
2.42
-1.00
NoUrbNoAnth
-2.00
-3.00
UrbNoAnth
UrbAnth
RMSE
1.48
1.51
1.39
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.
Urban model bias – Athens case

greatest impact of
anthropogenic waste
heat on the UHI during
winter
gridcell-5
3
2.5
2
1.5

during summer, it
becomes a small term
relative to the solar
forcing
1
UrbAnth-NoUrbNoAnth
0.5
UrbNoAnth-NoUrbNoAthn
0
0
2
4
6
8
10
12
5
Model evaluation
23
1
2
3
4
7
5
6
8
9
23.5
24
24.5
25
Summer Daytime/Nocturnal UHI
UHIurban-rural
UHIurban-rural
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
0.16
4.55
obs
0.16
4.55
obs
0.16
4.55
NoUrbNoAnth
1.14
2.72
UrbNoAnth
1.06
4.57
UrbAnth
1.07
4.75
RMSE
0.98
1.83
RMSE
0.9
0.02
RMSE
0.91
0.2
UHIurban-suburban
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
0.59
3.77
obs
0.59
3.77
obs
0.59
3.77
NoUrbNoAnth
1.07
0.45
UrbNoAnth
1.16
2.21
UrbAnth
1.13
2.39
RMSE
0.48
3.32
RMSE
0.57
1.56
RMSE
0.54
1.38
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
0.55
4.39
obs
0.55
4.39
obs
0.55
4.39
NoUrbNoAnth
0.71
2.00
UrbNoAnth
0.71
3.93
UrbAnth
0.77
4.11
RMSE
0.16
2.39
RMSE
0.16
0.46
RMSE
0.22
0.28
Winter Daytime/Nocturnal UHI
UHIurban-rural
UHIurban-rural
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
1.50
3.50
obs
1.50
3.50
obs
1.50
3.50
NoUrbNoAnth
1.38
-0.07
UrbNoAnth
1.44
1.69
UrbAnth
1.51
1.99
RMSE
0.12
3.57
RMSE
0.06
1.81
RMSE
0.01
1.51
UHIurban-suburban
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
1.40
3.00
obs
1.40
3.00
obs
1.40
3.00
NoUrbNoAnth
0.38
0.67
UrbNoAnth
0.45
1.94
UrbAnth
0.5
2.13
RMSE
1.02
2.33
RMSE
0.95
1.06
RMSE
0.90
0.87
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
obs
1.20
3.40
obs
1.20
3.40
obs
1.20
3.40
NoUrbNoAnth
0.77
-1.09
UrbNoAnth
0.81
0.68
UrbAnth
0.87
1.04
RMSE
0.43
4.49
RMSE
0.39
2.72
RMSE
0.33
2.36
Future Projections of UHI for summer
UHIurban-rural
UHIurban-rural
UrbNoAnth
daytime
0.97
nocturnal
4.67
UrbAnth
daytime
1.05
nocturnal
4.66
Urb3Anth
daytime
1.12
nocturnal
5.16
%
-8.5
2.2
-1.9
-1.9
4.7
11.0
UHIurban-suburban
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
UrbNoAnth
1.14
2.17
UrbAnth
1.17
2.29
Urb3Anth
1.27
2.72
%
-1.7
-1.8
3.5
-4.2
11.4
18.3
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
UrbNoAnth
0.83
4.40
UrbAnth
0.75
4.18
Urb3Anth
0.86
4.69
%
16.9
12.0
-2.6
1.7
16.2
16.7
Future Projections of UHI for winter
UHIurban-rural
UHIurban-rural
UrbNoAnth
daytime
0.97
nocturnal
4.67
UrbAnth
daytime
1.05
nocturnal
4.66
Urb3Anth
daytime
1.12
nocturnal
5.16
%
-8.5
2.2
-1.9
-1.9
4.7
11.0
UHIurban-suburban
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
UrbNoAnth
0.41
1.99
UrbAnth
0.52
2.15
Urb3Anth
0.65
2.46
%
-8.9
2.6
4.0
0.9
38.3
21.8
daytime
nocturnal
daytime
nocturnal
daytime
nocturnal
UrbNoAnth
1.09
1.26
UrbAnth
0.88
0.95
Urb3Anth
1.06
1.52
%
34.6
85.3
1.1
-8.7
26.2
90.0
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 Athens
temperature
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 well
future
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).