national observatory of athens insitute for environmental research and sustainable development...

NATIONAL OBSERVATORY OF ATHENS

INSITUTE FOR ENVIRONMENTAL RESEARCH AND SUSTAINABLE DEVELOPMENT

Manifestation ofManifestation of climatic climatic changechange from long term from long term observations inobservations in Eastern Eastern

MediterraneanMediterranean – –

The role ofThe role of urban effecturban effect

D. Founda, M. Petrakis, C. Giannakopoulos

National Observatory of Athens, Institute for Environmental Research and Sustainable Development



“Look into the past to see the future”

Climatic research worldwide is based on historical records and long term observational data

Climatic change: the result of natural climate variability + variations due to anthropogenic driving forcing

Natural climate variability: solar radiation, volcanic activity, aerosols concentration, ocean circulation etc..

Anthropogenic: GHG concentrations, Land use/Land cover changes



Global warming

The ‘average’ surface air temperature of the Earth (land + oceans) rose by approximately 0.740 C over the last 100 years

The warming rate is higher in the second half of the century

Warming rate in the Northern Hemisphere is higher than in Southern Hemisphere

Large spatial variability in climate change

It is quite important to study climate changes on regional or local scales

Seasonal variability



Air temperature trends in E. Mediterranean- Seasonal differentiations

E. Mediterranean (June-August)

E. Mediterranean (Dec-Feb)

From NCEP/NCAR database



Seasonal differentiations

Long term variation of air temperature in three cities of E. Mediterranean in winter



Seasonal differentiations

Long term variation of air temperature in three cities of E. Mediterranean in summer



Climatic research in Greece and Eastern Mediterranean is inevitably connected with the historical records of National Observatory of Athens (NOA)

The oldest Research Institute of the country and one of the oldest ones in Eastern Mediterranean and Southeastern Europe, founded in 1842

The historical record of NOAThe historical record of NOA



• First meteorological observations in Athens in 1833 – not complete record until 1858

•Since 1858 uninterrupted measurements in Athens – relocation of the station within the centre of the city

•Since 1890, a complete, continuous and reliable climatic record at the same location in Athens (Thission - near Acropolis)

•Perhaps the most important contribution of NOA in the study of climate in Greece

The historical record of NOAThe historical record of NOA



Also,

In 1894 NOA installed a national network of more than 30 meteorological stations at several places of the country

Measured meteorological parameters: air temperature, atmospheric pressure, humidity, wind speed-direction, precipitation, cloudiness (3 observations/day)

In 1932, the network was undertaken by the newly established HNMS.



Today,

Two A' class meteorological stations at Thission (historical) and Penteli (since 1998)

•Air temperature- soil temperature at several depths

•Humidity of the air -Atmospheric pressure

•Wind speed-direction

•Precipitation, cloudiness

•Sunshine duration

•Solar radiation (since 1954)

•Sunshine duration

•Illuminance (since 1992)

•Visibility



Variety of local climates in Greece

Need for a dense network of stations

161 automatic met stations (Davis) installed by NOA

Data available to the public online



Past Climate in Greece-Air temperature Past Climate in Greece-Air temperature trendstrends

According to the results from several studies (e.g Feidas et al., 2004, Philandras et al., 2010):

• A cooling in the annual temperature in Greece from 1951-1976 (statistically significant) is observed

• More pronounced in continental areas of Northern Greece (e.g 0.60C/decade at Trikala)

• The decade of 1970, the coldest one over Hellenic region.

• Seasonal analysis indicated cooling trends in both winter and summer seasons from 1951-1976 (statistically significant and more pronounced in summer)



Past Climate in Greece-Air Past Climate in Greece-Air temperature trendstemperature trends

A warming in the annual temperature in Greece from 1976 and onwards is observed

This is mainly due to positive trends in summer temperature (Athens and continental areas of Northern Greece experience the most pronounced warming in summer 10 C/decade)

In winter, most parts of Greece reveal no significant negative trends



20

21

22

23

24

25

1860 1880 1900 1920 1940 1960 1980 2000

Year

Air

tem

pera

ture

(ο

C)

NOANOA follows the large scale air temperature follows the large scale air temperature variations of the variations of the Northern HemisphereNorthern Hemisphere

Annual air temperature at NOA for the last 150 years

mean annual temp. at NOA

16

17

18

19

20

1895 1915 1935 1955 1975 1995 2015

Air

te

mp

era

ture

(C

)

annual mean maximum temp at NOA

202122232425

1895 1915 1935 1955 1975 1995 2015Air

tem

per

atu

re (

C)

annual mean minimum temp. at NOA

12.5

13.5

14.5

15.5

16.5

1895 1915 1935 1955 1975 1995 2015

Year

Air

te

mp

era

ture

(C

)

Variation of annual mean, maximum and minimum temperature at NOA

(1897-2010)2010



Mean summer temperature at NOA (1897-2010)

Trends 1897-2010: + 0.160 C/decade, or ~ 1.80 C

Trends 1976-2010: +0.9 0 C/decade, or ~ 30 C

Mean summer temperature at NOA

24

25

26

27

28

29

30

1880 1900 1920 1940 1960 1980 2000 2020

year

Air

tem

per

atu

re (

C)



Mean winter temperature at NOA (1897-2010)

Trends 1897-2010: +0.020 C/decade, or ~ 0.220 C

Trends 1976-2010: +0.15 0 C/decade, or ~ 0.50 C

Mean winter temperature at NOA

6

7

8

9

10

11

12

13

1880 1900 1920 1940 1960 1980 2000 2020

year

Air

tem

per

atu

re



Temperature extremes

What is extremeWhat is extreme??

Use of threshold values

Link with catastrophic events

Use of percentiles

• The value of 323200CC is not extreme in Athens but is not extreme in Athens but it is extreme in Moscowit is extreme in Moscow. .

• The value of 101000C is not extreme in March in C is not extreme in March in Athens but it is extreme in June.Athens but it is extreme in June.

•An increase in the mean maximum temperature from 353500CC to 373700CC can increase mortality

•An increase in the mean maximum temperature from 225500CC to 227700CC will have an impact on ecosystem



1970 1975 1980 1985 1990 1995 2000 2005

YEAR

3 5

3 6

3 7

3 8

3 9

4 0

4 1

4 2

4 3

4 4

Tem

pera

ture

thre

shol

d

1

11

21

31

41

The value of The value of 335500CC corresponds to the corresponds to the 9090thth percentile in summer in Athens (for the percentile in summer in Athens (for the period 1961-1990)period 1961-1990)..

Temperature extremes



Use of thresholds

Daily Tmax> 37 0 C (close to human body temperature, roughly 95th percentile)

Daily Tmax > 40 0 C (psychological threshold value for Athenians – several activities paralyze)

131 out of the 381 hot days (150 year period) occurred during 2001-2010.

0

5

10

15

20

25

30

Year

Num

ber

of d

ays/

year >37deg >40deg



A sequence of at least 3 consequtive days with Tmax above a threshold value. Changes in:

Frequency of occurrence

Duration

Heat wavesHeat waves

Number of heat waves >37 deg

0

1

2

3

4

5

1864 1874 1884 1904 1914 1924 1934 1944 1954 1964 1974 1984 1994 2004 2014

Year

Nu

mb

er o

f h

eat

wav

es

Number of heat waves/year in Athens for the last 150 years



1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

YEAR

35.0

35.5

36.0

36.5

37.0

37.5

38.0

38.5

39.0

39.5

40.0

40.5

41.0

Tem

per

atu

re t

hre

sho

ld

3

4

5

6

7

8

9

Mean duration (days) of warm episodes in Athens during the last

century



1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

YEAR

5

10

15

20

25

30

DA

TE

OF

MA

Y

1 8

1 9

2 0

2 1

2 2

2 3

2 4

2 5

2 6

2 7

2 8

2 9

A shift of the occurrence of hot days earlier in May





A case study: Summer 2007Summer 2007 in Greece. How extreme was itHow extreme was it?

All time record summerAll time record summer with respect to

Highest temperature ever recorded at NOA (44.8(44.8)) (previous record 4343 00CC in June 1916)

Mean summer Tmax (34.9 (34.9 00CC)) ( climatic value 31.631.6 0C)

Mean summer Tmin (24.4 (24.4 00CC)) (climatic value 21.6 21.6 00CC)

Number of days > 373700CC (2626 totally)

Number of days >404000CC (88 totally)





The most important impact of the extremely hot and dry conditions in Greece during summer 2007 was the ignition of the most destructive forest fires of the country.

Soil dehydration, following the prolonged dry period in combination with hot temperatures and strong winds in summer 2007, yielded favorable conditions for the ignition and spread of forest fires.These fires were responsible for the destruction of 2% of the Greek land surface and the death of 64 humans.



28

29

30

31

32

33

34

35

36

1890 1905 1920 1935 1950 1965 1980 1995 2010

year

Mea

n s

um

mer

tem

per

atu

re

(o C

)

0.00E+00

5.00E+05

1.00E+06

1.50E+06

2.00E+06

2.50E+06

3.00E+06

3.50E+06

Bu

rned

surface (acres)

2007



More RecordsMore Records

20102010: the warmest year ever (: the warmest year ever (19.619.600 C C- - 17.7 17.7 climatic valueclimatic value) after 2007 (19.1)) after 2007 (19.1)

All months of 2010 were much warmer than All months of 2010 were much warmer than their climatic values, but their climatic values, but

AugustAugust was the warmest August ever was the warmest August ever ((36.136.100 C C, mean maximum temp-, mean maximum temp-32.3 climatic 32.3 climatic valuevalue ) )

NovemberNovember was the warmest November ever was the warmest November ever ((3.53.500 warmer from its normal value warmer from its normal value))

Decade 2001-2010Decade 2001-2010 the warmest decade the warmest decade ever.ever.

(six out of the warmest years occurred (six out of the warmest years occurred during the decade 2001-2010)during the decade 2001-2010)

June 2010June 2010: the : the earliest heat waveearliest heat wave ever ever



Global warming or urbanization?Global warming or urbanization?

Urban Heat Island (UHI)Urban Heat Island (UHI) – a well documented – a well documented phenomenon in cities expressed as the phenomenon in cities expressed as the temperature difference between urban and temperature difference between urban and surrounding rural areassurrounding rural areas

Urban heat islands 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.



Removal of urban influenceRemoval of urban influence for the estimationfor the estimation

ofof global warmingglobal warming

‘‘Urbanization adjustments’Urbanization adjustments’ (statistical adjustments)(statistical adjustments)

Removal of urban stations from networkRemoval of urban stations from network

However, However,

In large cities : In large cities :

Additive effect of Additive effect of global warming + urbanizationglobal warming + urbanization

Greatest Greatest impacts in all sectorsimpacts in all sectors health, energy, health, energy, economyeconomy

(etc), due to (etc), due to higher population densityhigher population density

Global warming or urbanization?Global warming or urbanization?In their effort to estimate global warming scientist In their effort to estimate global warming scientist usuallyusually decide….decide….



Significant research on UHI in Athens Significant research on UHI in Athens

(e.g Katsoulis and Theoharatos 1985; Philandras et al., 1999; Santamouris et al., 2001, 2007; Livada et al., 2005 etc).

UHI in AthensUHI in Athens, of the order of , of the order of 4-54-500 C C between between urban urban and and suburbansuburban stations (Livada et al, 2005) stations (Livada et al, 2005)

ButBut

UHIUHI can be of the order of can be of the order of 101000 C C between between rural stationsrural stations and the and the central zonecentral zone



Significant research on Significant research on spatial variabilityspatial variability of UHI in Athensof UHI in Athens

Studies concerning the Studies concerning the rates of changes rates of changes ofof UHI over UHI over time time are missing are missing

It is important to know whether the It is important to know whether the intensity of the urban heat islandintensity of the urban heat island in a in a city continues to city continues to amplifyamplify, if it , if it hashas moderatedmoderated or or has has stabilizedstabilized

Trends of UHITrends of UHI



NOA urban in a park (unchanged

surrounding on local/micro scale)

Helliniko(HEL) urban coastal

Tatoi(TAT) rural / suburban

Tanagra (TAN) rural (military airport)

Aliartos (ALI) rural

Comparison of air temperature trends between..



y = 0,0918x - 150,12

y = 0,1003x - 168,62

28293031323334353637

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Year

Sum

mer

max

tem

pera

ture

HEL max NOA maxLinear (NOA max) Linear (HEL max)

Summer maximumSummer maximum temperature at temperature at NOA (urban)NOA (urban) and and HEL (coastal urban)HEL (coastal urban) stations stations

Similar trendsSimilar trends



Summer average temperature

22

23

24

25

26

27

28

29

30

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Year

Air

tem

per

atu

re rural1

rural2

urban1

urban2

Summer maximum and minimum tempearure

0

5

10

15

20

25

30

35

40

1970 1980 1990 2000 2010 2020

Year

Air

tem

per

atu

re

rural1(max)

rural1(min)

rural2(max)

rural2(min)

urban1(max)

urban1(min)

urban2(max)

urban2(min)

Changes in average, maximum and minimum temperature



Temporal variation of UHI

y = 0,0403x - 79,433

y = 0,0403x - 79,989

-0,8

-0,4

0

0,4

0,8

1,2

1,6

1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

Su

mm

er U

HI

(C)

NOA-TAN (avg) HEL-TAN(avg)Linear (HEL-TAN(avg)) Linear (NOA-TAN (avg))

Temporal variation of UHI

y = 0,0214x - 41,927

y = 0,0214x - 41,385

-0,5

0

0,5

1

1,5

2

2,5

1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

UH

I (C

)

HEL-TAT(avg) NOA-TAT(avg)Linear (NOA-TAT(avg)) Linear (HEL-TAT(avg))

Summer UHI trendsSummer UHI trends

UHI (Turban –Trural)

UHI (Turban – Tsuburban)



y = -0,0008x + 11,586

y = -0,0005x + 11,589

6

7

8

9

10

11

12

13

1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

Air

tem

pera

ture

(C)

HEL avg NOA avg

Linear (NOA avg) Linear (HEL avg)

WinterWinter temperature at temperature at NOA (urban)NOA (urban) and and HEL (coastal urban)HEL (coastal urban) stations stations

Similar trends (no significant trend)Similar trends (no significant trend)



Winter UHI trendsWinter UHI trends

UHI (Turban –Trural)

UHI (Turban – Tsuburban)

y = 0,02x - 37,871

y = 0,0203x - 37,867

0

0,51

1,52

2,53

3,5

1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

UH

I (C

)

NOA-TAN avg HEL-TAN avgLinear (NOA-TAN avg) Linear (HEL-TAN avg)

y = 0,0105x - 17,945

y = 0,0101x - 17,949

0

1

2

3

4

1970 1975 1980 1985 1990 1995 2000 2005 2010

year

UH

I (C

)

HEL-TAT avg NOA-TAT avgLinear (HEL-TAT avg) Linear (NOA-TAT avg)



Cases of Cases of heat wavesheat waves in a in a citycity

MaximumMaximum (Day) temperature (Day) temperature

Maximum temperature-Summer 2007

20

25

30

35

40

45

50

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89

Summer day

Air

tem

pera

ture

Athens Elefsis

During heat waves, maximum (day) temp. in the city (Athens) is lower to the one at the rural /Industrial area of Elefsis



Cases of Cases of heat wavesheat waves in a city in a city

MinimumMinimum (Night)(Night) temperature temperature

Mininum temperature -Summer 2007

15171921232527293133

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89

Summer day

Air t

empe

ratu

re

Athens Elefsis

HeatWave1

During heat waves, minimum (night) temp. in the city (Athens) is much higher than at the rural /Industrial area of Elefsis



Some conclusionsSome conclusions

SummerSummer air temperature trends after 1976 at air temperature trends after 1976 at two two urban urban stations in Athens are of the order of stations in Athens are of the order of 1100 C/decade C/decade

UHIUHI in in summersummer increases at a rate of the order of increases at a rate of the order of 0.40.400C /decadeC /decade (rural-urban) or (rural-urban) or 0.2 0.2 00/decade/decade (urban –suburban)(urban –suburban)

RoughlyRoughly

““60%60% of warming is due to of warming is due to global warmingglobal warming and and the rest the rest 40%40% is due to is due to urban effect’urban effect’



Some conclusionsSome conclusions

WinterWinter air temperature air temperature after 1976after 1976 at two at two urbanurban stations in Athens reveal stations in Athens reveal no no significant trendsignificant trend

UHI in winter,UHI in winter, increases at a rate of the increases at a rate of the order of order of 0.2 0.2 00/decade/decade

UHI compensates the possible decrease of UHI compensates the possible decrease of air temperature in winterair temperature in winter



Significant increase of summer air temperature in Greece and especially in Athens, after the mid 70’s

Decade 2001-2010: the warmest ever in Athens

Pronounced increase in the frequency of hot days, heat waves

Summer 2007: the most extreme summer in Athens according to NOA’s temperaure record.

YEAR 2010: the warmest year ever in Athens

Less important variations during the cold period of the year

UHI accounts partly for the significant increase of the mean temperature in Athens

Night temperatures at urban areas much higher, especially during severe heat waves- threat for human health and mortality

General Conclusions

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