INTERNATIONAL JOURNAL OF CLIMATOLOGY
Int. J. Climatol. 23: 1771–1796 (2003)
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.962
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY LINKED TO
THE NORTH ATLANTIC OSCILLATION DURING THE PERIOD 1930–2000
a
MURAT TÜRKEŞa, * and ECMEL ERLATb
Department of Research, Turkish State Meteorological Service, Ankara, Turkey
b Department of Geography, University of Aegean, Bornova — İzmir, Turkey
Received 18 November 2002
Revised 18 August 2003
Accepted 18 August 2003
ABSTRACT
Relationships between the variability of the North Atlantic oscillation (NAO) indices and the normalized precipitation at
78 stations in Turkey, and the influences of the extreme NAO index (NAOI) episodes and the year-to-year and longer
time-scale variations in the NAO on the precipitation conditions were investigated. The results of the study have led to
the following main conclusions and evaluations for Turkey:
(i) There is a negative relationship between interannual variability of the Turkish precipitation series and the NAO
indices. Negative relationships that are particularly strong in winter and partly in autumn are detected to be weaker in
spring and almost non-existent in summer. Correlation coefficients are significant at 61 stations in winter, whereas they are
significant at 23 and eight stations in autumn and spring respectively. (ii) Composite precipitation means corresponding to
the extreme NAOI phases mostly exhibit an apparent opposite anomaly pattern, except in summer, between the negative
and positive NAOI phases. (iii) Annual, winter, spring, autumn and partly the summer composite precipitation means
are mostly characterized by wetter than the long-term average conditions during the negative NAOI phase, whereas the
positive NAOI responses mostly exhibit drier than the long-term average conditions annually and in all seasons except
summer. (iv) Spatially coherent and statistically significant changes in the precipitation amounts during the extreme NAOI
phases are more apparent in the west and mid Turkey. (v) Low-frequency fluctuations in the circulation over the Atlantic
have been closely linked to the coherent large-scale precipitation anomalies that have persisted, particularly in winter,
over Turkey since the early 1960s. (vi) There is a great resemblance between the spatial distribution and magnitude of the
negative correlation coefficients and the spatial distribution patterns and severity of the wet (dry) conditions with negative
(positive) NAOI phase, annually and in the winter and autumn seasons. (vii) The coherent regions characterized with
significant correlation coefficients coincide perfectly with the coherent regions characterized by the extreme NAOI signals.
These clear associations increase our confidence with the results. Copyright  2003 Royal Meteorological Society.
KEY WORDS:
Turkey; precipitation; the North Atlantic oscillation; the NAO index; extreme NAOI phases; composite precipitation
anomaly and mean; correlation and Cramer’s tk test
1. INTRODUCTION
The atmospheric circulation and its year-to-year and decadal variations are accepted as the main determinants
and/or controls on the Earth’s climate and the large-scale climatic variability. Variations in many climatic
variables are strongly related through large-scale features of the atmospheric circulation, as well as through
interactions involving the land and ocean surfaces (Nicholls et al., 1996). The well-known El Niño–southern
oscillation (ENSO) and the North Atlantic oscillation (NAO) are probably the most-studied examples of such
large-scale regional features.
The NAO has been considered as one of the most important teleconnection patterns: it significantly affects
Atlantic weather patterns and produces regional climatic anomalies associated with itself, particularly in
Europe and the Mediterranean Basin. The NAO can be defined as a large-scale swaying of atmospheric
* Correspondence to: Murat Türkeş, Department of Research, Turkish State Meterological Service, PO Box 401, Ankara, Turkey.
Copyright  2003 Royal Meteorological Society
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M. TÜRKEŞ AND E. ERLAT
NAO Index
pressure between the dynamic subtropical anticyclone centred over the Azores region and the extratropical or
the mid-latitude cyclone dominating over the Iceland and Greenland region in the North Atlantic. Normalized
NAO indices (NAOIs) are developed in order to evaluate the behaviour of the NAO and the regional
climate anomalies linked to the extreme NAO episodes. An NAOI is generally calculated as the difference of
normalized sea-level pressures (SLPs) between a station in the area of the Azores and a station in Iceland (i.e.
the Azores high–Icelandic low (IL) pressure gradient). The SLP anomalies at each station are normalized by
division of each monthly pressure by the long-term standard deviation.
The importance of, and the scientific interest in, the NAO has increased, and so many studies have been
performed, especially for the North Atlantic, Europe and the Mediterranean basin since the early 1990s,
because the NAOIs were mostly characterized by a persistent positive anomaly episode dominating over the
years of the 1980s and 1990s (Figure 1). Hurrell (1995), based on an evaluation of the atmospheric moisture
budget, revealed that coherent large-scale changes since 1980 were linked to dry conditions over southern
Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia generally experienced
wetter than normal conditions. Hurrell and van Loon (1997) explained that precipitation anomalies (including
dry wintertime conditions over southern Europe and the Mediterranean regions, and the wetter than normal
conditions over northern Europe and Scandinavia since 1980) were also linked to the behaviour of the NAO.
Serreze et al. (1997) examined the characteristics of cyclone activity associated with the locus of the mean IL,
variability during the extremes of the NAO and (recent) changes in relation to circulation over the Northern
Hemisphere for the period 1966–93. They indicated a twofold decrease in cold-season cyclone events within
NAO Winter
5
1989-94(1.85)
4
1973(2.4)
3
2
1
0
-1
-2
-3
-4
1963(-4)
-5
1963-69(-2.92)
-6
1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
5
NAO Annual
1989-94(2.4)
4
NAO Index
3
2
1
0
-1
-2
-3
-4
1963-69(-2.2)
-5
1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
Figure 1. Long-term variations in the annual and winter NAOI (Ponta Delgada, the Azores–Stykkisholmur/Reykjavik, Iceland) anomalies.
) with padded ends
Interannual variations are smoothed by the nine-point Gaussian filter (
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
1773
the climatological IL during the negative NAO extremes, with accompanying reductions in intensity, but little
change in maximum deepening rates. Serreze et al. (1997) attributed this to the modest increases in activity
to the south over a large area from Labrador eastward to Portugal, reflected in the southward movement
and weakening of the sub-polar low. Kapala et al. (1998), based on the analysis of the behaviour of action
centres in the Atlantic since 1881, showed that the positive NAO phase in winter led to a warming over
northern and central Europe as well as to the development of dipole-like anomaly patterns in the wind speed,
sea-surface temperature (SST), surface and tropospheric temperatures and other variables in the western and
eastern North Atlantic. The negative NAO phase revealed the inverse patterns.
A number of studies were also performed for the influence of the NAO and the southern oscillation (SO)
on climatic variability and anomalies over the Mediterranean basin and the surrounding countries and/or
regions (e.g. Rodo et al., 1997; Türkeş, 1998a, 2000; Wibig, 1999; Delitala et al., 2000; Camuffo et al.,
2000; Hasanean, 2001; Ben-Gai et al., 2001; Mariotti et al., 2002). The main findings and conclusions from
some of those studies are summarized as follows: Rodo et al. (1997) revealed that both the NAO and the SO
influenced the seasonal rainfall of the Iberian Peninsula, but at different temporal and spatial scales. They
indicated that most of the peninsula, except some stations in the eastern region, was under the influence
of the NAO in winter. The influences of the warm and cold events of the SO, especially on the winter
precipitation of Turkey and on the severe and widespread winter droughts that occurred after 1970 over
Turkey associated with the ENSO events and the atmospheric conditions, were examined by Türkeş (1998a,
2000). Türkeş (1998a) revealed that most of the 48 stations selected had a positive sign anomaly during
year − 1 warm events and cold events, and the cold-event precipitation means showed a coherent region of
significantly increased precipitation conditions over the central-west and central parts of Turkey. On the other
hand, most of the warm- and cold-event responses were characterized by a decreased precipitation, and drier
than long-term average conditions were significant at some stations during year + 1 cold events. The warmminus cold-event differences had an opposite signal between year − 1 and year 0 (+1) at many stations.
Opposition of composite anomalies were also evident at most of the stations between year − 1 and year +
1 cold events. Wibig (1999) found a good relationship between the precipitation in western Europe and the
NAOI but the correlation coefficients decreased to zero in the Balkans and the eastern Mediterranean. BenGai et al. (2001) found significant correlation coefficients of −0.8 and +0.9 between the NAOI anomalies
and the smoothed cool-season temperature and SLP anomalies in Israel respectively. Mariotti et al. (2002)
found coherent correlation patterns between the variability of the Euro-Mediterranean rainfall and ENSO in
central and eastern Europe during winter and spring, and in western Europe and the Mediterranean region
during autumn and spring. They showed that the western Mediterranean rainfall during an El Niño had a
10% increase (decrease) in autumn preceding the mature phase of an event, corresponding to a rainy season
arriving (retreating) earlier compared with the climatology.
There are some studies on the streamflow variability and responses to the NAO and the ENSO anomalies,
too. Cullen and deMenocal (2000) investigated the influence of the NAO on the Tigris–Euphrates streamflow
and Turkey’s and the Middle Eastern climate. They found that composite indices of Turkish winter temperature
and precipitation were significantly correlated with the NAOI, accounting for 27% of the variance in
precipitation. They also revealed, as evident by the (recent) widespread drought events of 1984, 1989 and
1990, that the Tigris–Euphrates streamflows exhibited significant (±40%) variability associated with the
extremes. Kahya and Karabörk (2001), using an empirical methodology, detected the coherent streamflow
responses in Turkey to the El Niño and La Niña events in two core regions, namely northwestern Anatolia
(NWA) and eastern Anatolia (EA). In the Susurluk sub-region in NWA, the April–October seasonal positive
anomalies had a significant relation with the El Niño events. For the EA region, above-normal conditions
were observed during the April (0)–November (0) period and the May (0)–February (+) period for the El
Niño and La Niña events respectively.
Kutiel and Benaroch (2002) recently defined a new upper-level atmospheric teleconnection entitled the
North Sea–Caspian Pattern (NCP), and derived an index (NCPI) to evaluate the magnitude of the NCP.
The anomaly circulation in the eastern Mediterranean basin showed an increased southwesterly circulation
during the NCP (−) phase and an increased northeasterly circulation during the NCP (+) phase (Kutiel
and Benaroch, 2002). In a very recent study, Kutiel et al. (2002), based on the monthly mean temperatures
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
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M. TÜRKEŞ AND E. ERLAT
and monthly precipitation totals from 33 stations across Greece, Turkey and Israel, found that temperature
values were significantly higher during the NCP (−) compared with the NCP (+) at all stations and in all
months. They revealed that the regions exposed to the southern maritime trajectories, in Greece and in Turkey,
received above-normal precipitation during the NCP (−) phase, whereas in the regions exposed to the northern
maritime trajectories, such as Crete in Greece, the Black Sea region in Turkey and in all regions of Israel,
above-normal precipitation conditions dominated during the NCP (+) phase. The accumulated precipitation
differences between the two phases are over 50% of the seasonal average for some stations. They also made
a comparison of the capabilities of the NCP, the NAO and the SO indices to differentiate below- and abovenormal temperatures for Turkey. Their results placed the NCP as the best of three teleconnections in its ability
to differentiate between below- or above-normal temperatures, and as the main teleconnection affecting the
climate of the Balkans, the Anatolian Peninsula and the Middle East.
Preliminary results of recent studies on the relationships between Turkish precipitation and the NAO (Erlat,
2002) have pointed out that annual and, in particular, long winter (DJFM) precipitation amounts for the period
1930 to 2000 tended to decrease during the positive NAO phase and to increase during the negative NAO
phase. According to Erlat (2002), the period approximately from 1940 to 1970 generally consisted of marked
wet conditions in Turkey, whereas the period of 1971–94 was generally dominated by dry conditions. The
maximum annual and winter precipitation amounts occurred in the year 1963, corresponding to a marked
negative NAOI. Apparent decreased precipitation in the years of 1973 and 1989 corresponded with markedly
positive NAOI winters.
However, the relationships between the Turkish precipitation series and the NAOIs, and the spatial and
temporal patterns of the composite precipitation anomalies and conditions persisting for a particular period of
time linked to the extreme NAOI phases and the persistent extreme NAOI anomaly years respectively have
not yet been analysed in detail using the longest and most homogeneous annual and seasonal series with a
sufficient number of stations in Turkey. Therefore, the aim of the present study is as follows: (a) to detect the
statistical nature and magnitude of the relationship between variability of the normalized annual and seasonal
precipitation anomaly series for 78 stations in Turkey and variability of the NAOI anomalies; (b) to determine
the spatial and temporal patterns of the composite precipitation anomalies for 78 stations in Turkey linked to
the extreme (i.e. negative and positive) NAOI phases during the period 1930–2000; (c) to assess the statistical
significance of drier or wetter than long-term average precipitation conditions associated with the extreme
NAOI phases; and (d) to present some examples for the individual yearly and longer time-scale (i.e. quasi
decadal/decadal) precipitation responses to the NAOI, which are very likely explained by the influence of
corresponding year-to-year and persistent extreme NAOI anomalies occurring during the period 1960–2000.
The study was based on the longest and most homogeneous precipitation series with a sufficient number of
stations in Turkey. These stations perfectly represent both Turkey’s rainfall regions and Turkey as a whole.
Spatial evaluations of the results were performed by taking the rainfall regime regions of Turkey as delimited
by Türkeş (1996a, 1998a) into account.
2. DATA AND METHODOLOGY
In the study, the precipitation data set that was originally developed by Türkeş (1996a,b, 1998a) for a total
of 99 (91 + 8) stations and the period 1929–93 has been used, by updating it for the recent years from
1994 to 2000. The data set consisted of the monthly precipitation totals (mm) recorded at the stations of
the Turkish State Meteorological Service (TSMS). They are mostly principal climatological stations with a
very few ordinary and precipitation stations. The stations included in the original data set have been chosen
from about 130 stations by controlling the possible inhomogeneities, particularly those of non-climatic abrupt
(step-wise) changes in the monthly and seasonal series with the Kruskal–Wallis homogeneity test (Türkeş,
1996a,b). The results of the homogeneity tests were also checked by considering the information from the
station’s history file. Detailed information for the meta-data and the homogeneity analyses applied to the
long-term Turkish precipitation series can be found in Türkeş (1996a,b, 1999). The precipitation climatology
of Turkey and the long-term variability, trends and changes in the precipitation series were comprehensively
investigated previously by Türkeş (1996a,b, 1998a, 1999, 2003) and Türkeş et al. (2002).
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
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PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
The stations selected for this study (78) mostly have an approximate 70-year length of record. These stations
represent a very good spatial distribution over the rainfall regions of Turkey. The spatial distribution of the
78 stations over the rainfall regions is shown in Figure 2.
Annual and seasonal normalized precipitation anomaly series have been used in the study. A normalized
(standardized) precipitation anomaly Asy for a long series of a given station is calculated using
Asy = (Psy − P s )/σs
where Psy (mm) is total precipitation amount for a station s during a year y (or a season); P s and σs are
the long-term average and standard deviation of annual (or seasonal) precipitation series for that station
respectively.
The NAOI data used in the study was provided by the Climate Analysis Section, NCAR, Boulder, USA
and Hurrell (1995) (http://www.cgd.ucar.edu/∼jhurrell/nao.html). The seasonal/annual NAOIs were based on
the difference of normalized SLP between Ponta Delgada, the Azores and Stykkisholmur/Reykjavik, Iceland,
since 1865. Hurrell normalized the SLP anomalies at each station by division of each seasonal/annual pressure
by the long-term (1865–1984) seasonal/annual standard deviation.
In order to detect a possible relationship between the year-to-year variability in the precipitation anomalies
and the variability of the NAOI anomalies, and the nature and magnitude of the relationship, the Pearson’s
correlation coefficient r has been used. Statistical significance of the correlation coefficients has been checked
by the Student’s t test. By using the two-tailed test of the Student t distribution, the null hypothesis ‘absence
of any relationship between the precipitation and the NAOI series’ has been rejected for large values of |t|
with (N − 2) degrees of freedom.
In order to determine objectively the nature and magnitude of the precipitation responses in Turkey to the
variability of the NAO, both composite normalized precipitation anomalies and the composite precipitation
means corresponding to the extreme (negative and positive) NAOI phases have been computed for the annual
and seasonal series of each station. The composite analysis refers to a ‘negative’ (or weak) NAOI anomaly
phase corresponding to normalized NAO index values ≤−1.0 and a ‘positive’ (or strong) NAOI anomaly
phase corresponding to normalized index values ≥+1.0.
26°
42°
30°
32°
34°
36°
38°
40°
42°
44°
Sinop
K rklareli
BLACK
S E A
Lüleburgaz
Tekirdag
Zonguldak
Samsun
Göztepe
MRT
BLS
Kastamonu
Rize
Ardahan
Giresun
Sea of
Adapazari Bolu
Marmara
Merzifon
Trabzon
Amasya
Kars
Bilecik
Bayburt
CCAN
Çorum
Çanakkale Bandirma
Sar kam s
Ankara
Sebinkarahisar
Bursa
Edremit
Erzincan
Yozgat
Igd r
Balikesir
Kütahya Eskisehir
Erzurum
Sivas
Simav
Akhisar
K rsehir
Sivrihisar
Hns
CEAN
Usak Afyon
Manisa
.
Izmir
Kayseri
Elaz g
Van
Salihli
Ilg
n
MEDT
Aksaray
Malatya
Siirt
Aydin
Diyarbak r
Nigde
Konya
Ad yaman Siverek
Isparta
Mugla
Burdur
Uluk sla Kahramanmaras
Cizre
Karaman
Gaziantep
Antalya
CMED
Bodrum
0
80 160 240
Fethiye
Mersin Adana
Sanl
urfa
Kilis
km
Alanya
MED
38°
40°
42°
44°
Silifke
.
skenderun
Antakya
42°
40°
38°
36°
AEGEAN
SEA
40°
28°
Edirne
38°
36°
Rainfall regions and stations
MEDITERRANEAN
28°
30°
32°
SEA
34°
36°
Figure 2. Location of the 78 stations over the rainfall regions of Turkey. BLS: Black Sea; MRT: Marmara Transition; MED:
Mediterranean; MEDT: Mediterranean Transition; CMED: Continental Mediterranean; CCAN: Continental Central Anatolia; CEAN:
Continental Eastern Anatolia
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1776
M. TÜRKEŞ AND E. ERLAT
A comparison of the composite means corresponding to the extreme NAOI phases with the long-term
average precipitation totals has been made by means of the Cramer’s tk test, based on the null hypothesis of
‘no significant difference between a composite mean of the negative (positive) NAOI phase and the long-term
average of the whole period’. Cramer’s tk test (WMO, 1966) was applied previously by Türkeş to detect the
wet and dry periods in the regional precipitation series of Turkey (Türkeş, 1996a,b) and the warm and cold
SO event signals in the station-based precipitation series of Turkey (Türkeş, 1998a, 2000). The long-term
average P and standard deviation σ of the entire period with N years, and the composite mean P k of the
individual years Pi compared with P corresponding to negative (positive) NAOI anomaly years are defined
as follows:
P = (1/N )
σ =
N
N
Pi
i=1
1/2
(Pi − P )/N
i=1
P k = (1/n)
n
Pi
i=1
The normalized anomaly τk and the test statistic tk are computed by the following formulas:
τk = (P k − P )/σ
tk = τk [n(N − 2)/(N − n − nτk2 )]1/2
The test statistic tk is distributed as the Student’s t with N − 2 degrees of freedom. The null hypothesis of the
test is rejected with the two-tailed test for large values of |tk |. Any composite precipitation mean of a station
is considered as a dry (wet) ‘signal’ only if the test statistic of tk computed for that station is significant at
the 0.05 level of significance.
Both 0.05 and 0.01 levels of significance are taken into consideration for all hypothesis tests in this study.
Nevertheless, the term ‘significant’ used in the text should be taken as meaning the 0.05 level.
3. RESULTS OF THE ANALYSIS
All the results from the tests are presented by means of maps, and the results of the composite analysis for the
annual, winter and autumn precipitation are given in table format with additional information. In the tables,
the rank of a station for each rainfall region was determined by taking into account the sub-regional, local
and/or micro-climatological precipitation characteristics of that station by Türkeş (1996a, 1998a).
3.1. Annual NAOI responses
According to the results of the correlation analysis, negative correlation coefficients (CCs) are detected
between the year-to-year variability of the normalized annual precipitation series and the NAOI anomalies at
most of the stations, except those over the mid-eastern Black Sea and the northeastern Anatolia sub-regions
(Figure 3(a)). Negative CCs are statistically significant at 27 stations, most of which are located in the regions
of the Marmara Transition (MRT), the Mediterranean Transition (MEDT) and the Continental Central Anatolia
(CCAN) rainfall regions, and the northwestern part of the Mediterranean (MED) region. On the other hand,
the relationships are reversed over the far northeastern part of Turkey (Figure 3(a)). By considering these
results, it is expected that annual precipitation responses, particularly over areas of significant negative CC,
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
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PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
28°
32°
36°
44°
40°
BLACK
SEA
Sea of
Marmara
40°
AEGEAN
SEA
40°
36°
36°
(a) Correlation coefficients
between the annual NAO index
and the normalized precipitation
M E D IT E R R A N E A N S E A
0
50 100 150 200 250
km
28°
28°
0.35
Sea of
Marmara
0.31
0.26
SEA
0.53
0.45
0.46
0.34
0.22
0.18
-0.17
-0.04
0.03
0.30
0.14
0.02
0.12
0.19
0.02
0.08
0.13
-0.02
36°
(b) Composite annual
precipitation anomalies for the
negative NAO annual index phase
km
32°
-0.16
-0.36 -0.08
-0.15
-0.58
-0.50
SEA
-0.10
-0.48
-0.38
-0.31 -0.23
-0.47
-0.57
-0.17
-0.30
-0.21
AEGEAN
-0.29 -0.20
-0.14
0.05
0.00
-0.18
0.10
-0.15
-0.22
40°
-0.13
-0.09
-0.12
-0.01
-0.19
-0.22
0.06
-0.06
-0.36
-0.22
-0.04
0.04
-0.03
0.01
0.06
-0.03
0.05
0.03
36°
(c) Composite annual
precipitation anomalies for the
positive NAO annual index phase
km
32°
-0.01
-0.10
-0.18
M E D IT E R R A N E A N S E A
28°
0.10
-0.28
-0.08
-0.26
-0.15
50 100 150 200 250
-0.00
-0.06
-0.05
-0.28
-0.29
36°
0
44°
-0.13
-0.28
-0.26
-0.23
-0.24
-0.02
-0.29
-0.28
40°
-0.13
-0.32
-0.39
-0.12
-0.21
44°
SEA
-0.02
-0.41
0.13
40°
36°
BLACK
-0.44
-0.33
40°
36°
32°
Sea of
Marmara
-0.05
-0.00
M E D IT E R R A N E A N S E A
28°
0.05
0.07
-0.02
0.02
.
0.29 -0.02
0.18
0.12
-0.27-0.39
-0.16
-0.19
40°
0.01
-0.01
0.31
0.32
0.24
0.40
28°
-0.17
-0.10
0.14
-0.03
0.42
50 100 150 200 250
-0.14
0.12
0.23
0.48
36°
0
-0.03
0.04
0.29
0.10
44°
-0.21 -0.09
0.20
0.17
0.50
0.63
0.17
0.25
40°
0.14
0.16
0.24
-0.00
0.29
0.25
0.27
AEGEAN
0.11
0.03
0.37 0.20
0.65
0.14
-0.31
44°
SEA
-0.05
-0.05
0.30
40°
36°
32°
BLACK
0.44
0.42 0.29
40°
36°
32°
36°
40°
44°
Figure 3. Spatial distribution of: (a) the correlation coefficients between the NAO annual index anomalies and the normalized annual
precipitation anomalies of 78 stations in Turkey (bold lines indicate significant correlation coefficients at the 0.05 level (0.30 > r ≥ 0.23)
and the 0.01 level (r ≥ 0.30)) and of the composite normalized precipitation anomalies; (b) during the negative and (c) the positive
NAO annual index phases (bold plus symbols (filled inverse triangles) show the significantly wetter (drier) than long-term average
precipitation conditions at the 0.05 level, according to Cramer’s test)
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
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M. TÜRKEŞ AND E. ERLAT
are characterized by wetter than long-term average (in short, wet) conditions and signals during the negative
(low index) NAO anomalies, whereas they are explained by the drier than long-term average (in short, dry)
conditions and signals during the positive (high index) NAO anomalies. This assumption may be attributed to
the fact that humid and cyclonic conditions show up generally over the Mediterranean basin during the lowindex NAO years, whereas dry and anticyclonic conditions generally dominate during the high-index NAO
years. NAOI correlation responses are weaker at the stations of the Black Sea (BLS) and the Continental
Eastern Anatolia (CEAN) regions, along with the Silifke–Mersin–Adana district in the eastern Mediterranean
sub-region of Turkey.
Composite normalized annual precipitation is characterized with a positive anomaly at 58 stations of the total
of 78 stations used in the study, except some stations over the BLS, the Continental Mediterranean (CMED)
and the CEAN rainfall regions during the negative annual NAOI phase (Figure 3(b)). Similar results were also
found for the differences between the composite annual precipitation means corresponding to the negative
annual NAOI phase and the long-term precipitation averages. Cramer’s tk test shows that the composite
precipitation means corresponding to the negative NAOI phase are significantly wet in comparison with the
long-term precipitation averages at 14 stations (Table I; Figure 3(b)). These stations with significantly wetter
than long-term average conditions (in short, wet signals) are mostly located over the MRT region, Aegean
sub-region of the MED region and the MEDT region of western Turkey.
Composite normalized annual precipitation computed for the positive annual NAOI phase indicates negative
anomalies at 67 stations in Turkey, except for some stations in the CEAN and the CMED regions (Table I;
Figure 3(c)). Composite negative anomalies are generally much stronger at stations in the northwestern part
of the country. Drier than long-term average conditions are significant at 19 stations according to Cramer’s
tk test. Positive NAOI signals are evident in the MRT, MED and MEDT regions of Turkey (Figure 3(c)).
3.2. Winter NAOI responses
Relationships between the normalized winter precipitation anomalies in Turkey and the winter NAOI
anomalies are mostly defined by a significant negative correlation. The CCs are significant at 61 stations, 47
of which are at the 0.01 level. Non-significant CCs are mostly found in the middle and eastern BLS and the
middle MED sub-regions, along with the mountainous areas of the northeastern and the southeastern subregions of the CEAN region. Negative CCs are seen to become stronger in the middle and western regions
of the country, whereas weak CCs are found in the coastal areas of the Mediterranean and the Black Sea
regions, and the Lake Van sub-region of the CEAN region (Figure 4(a)).
It is found that there are coherent large-scale and marked changes in the winter precipitation of Turkey
during the extreme winter NAOI phases: winter precipitation tended to increase in a negative winter NAOI
phase, whereas it tended to decrease in a positive winter NAOI phase. Composite precipitation anomalies
corresponding to the negative NAOI phase are positive at all stations, except the stations of Trabzon, Sinop
and Karaman. Cramer’s test revealed that the wet conditions are significant at 40 stations, 19 of which are at
the 0.01 level (Table II; Figure 4(b)). Coherent regions with increased precipitation signals dominate mainly
over the Aegean part and the Gulf of İskenderun of the MED region, and the MRT, MEDT, CMED and the
mid-north CCAN regions. Non-significant wet and some dry responses are found for stations on some parts
of the Mediterranean belt, the CMED and the BLS regions, and the southern and eastern parts of the CEAN
region (Figure 4(b)).
The positive winter NAOI responses in winter precipitation are explained by a marked composite negative
anomaly at all stations in Turkey except Trabzon on the eastern Black Sea coast (Table II; Figure 4(c)).
Composite precipitation means are significantly below the long-term average at 38 stations, 12 of which are
at the 0.01 level. Dry signals in winter are much more pronounced for the stations in the northwestern and
middle regions of Turkey.
Our results for the composite winter precipitation anomalies corresponding to extreme anomaly phases of
the NAOI have indicated some similarity and disparity compared with the results of a recent study carried
out by Cullen et al. (2002), which was focused mainly on the impact of the NAO variability on the Middle
Eastern climate and streamflow. Strongly positive precipitation anomalies over the eastern Black Sea and
the northeastern Anatolia sub-regions of Turkey found in Cullen et al. (2002) for the negative NAOI phase
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1779
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
Table I. Results of the composite analysis for the annual precipitation series of 78 stations in Turkey. The composite
normalized anomaly (CNA), composite original anomaly (CA), composite mean p and number of the years n for
the extreme NAO index years, and the long-term precipitation average P . The precipitation amount is in millimetres.
Significant negative and positive NAOI signals are marked in the p columns in bold
Region
Station
Negative NAO conditions
CNA
CA
P
p
n
2289.1
804.6
1234.4
726.3
648.5
1225.5
544.3
783.7
23
23
23
23
23
23
23
22
Positive NAO conditions
CNA
CA
2299.7
816.7
1270.2
710
654.9
1237
541.5
822.3
−0.28
−0.01
−0.06
−0.13
−0.02
−0.16
−0.21
+0.13
−107.4
−0.8
−10.8
−14.5
−2.4
−34.0
−19.5
15.9
p
n
2192.3
815.9
1259.4
695.5
652.5
1203.0
522.0
838.2
28
28
28
28
27
27
28
25
BLS
Rize
Trabzon
Giresun
Samsun
Sinop
Zonguldak
Bolu
Adapazarı
−0.03
−0.09
−0.21
+0.14
−0.05
−0.06
+0.03
−0.31
−10.6
−12.1
−35.8
16.3
−6.4
−11.5
2.8
−38.6
MRT
Göztepe
Lüleburgaz
Kırklareli
Edirne
Tekirdaǧ
Bilecik
Bursa
+0.35
+0.29
+0.44
+0.42
+0.30
+0.20
+0.37
42.5
37.0
59.5
56.9
38.9
15.3
47.5
723.1∗
628.5
622.3∗
645.9∗
615.2
456.6
745.1∗
23
21
23
23
23
23
23
680.6
591.5
562.8
589.0
576.3
441.3
697.6
−0.42
−0.16
−0.39
−0.27
−0.19
−0.08
−0.36
−49.9
−20.2
−53.2
−36.5
−25.4
−6.2
−45.5
630.7∗∗
571.3
509.6∗
552.5
550.9
435.1
652.1∗
28
24
28
28
28
28
28
MED
Çanakkale
Bandırma
Balıkesir
Edremit
Akhisar
Simav
Salihli
Manisa
İzmir
Aydın
Muǧla
Bodrum
Fethiye
Antalya
Alanya
Silifke
Mersin
Adana
İskenderun
Antakya
+0.26
+0.31
+0.65
+0.53
+0.45
+0.63
+0.34
+0.46
+0.22
+0.27
+0.42
+0.14
+0.10
+0.20
+0.08
+0.12
+0.02
+0.13
+0.29
+0.18
34.8
45.9
76.6
89.9
59.7
120.2
34.2
74.7
37.3
38.7
133.8
26.8
22.5
57.7
20.6
24.1
3.0
23.7
47.4
49.9
650.4
742.6
654.6∗∗
798.2∗∗
647.3∗∗
935.6∗∗
522.1∗
802.8∗∗
723.6
683.3
1308.2∗
748.6
911.1
1119.0
1117.5
630.1
603.2
676.7
794.9
1179.8
23
23
22
22
23
22
22
23
22
23
23
22
22
23
18
23
23
23
22
22
615.6
696.7
578
708.3
587.6
815.4
487.9
728.1
686.3
644.6
1174.4
721.8
888.6
1061.3
1096.9
606
600.2
653
747.5
1129.9
−0.33
−0.44
−0.58
−0.50
−0.48
−0.57
−0.23
−0.38
−0.32
−0.28
−0.20
−0.29
−0.24
−0.19
−0.22
−0.15
+0.06
−0.06
−0.36
−0.22
−44.4
−65.0
−68.0
−84.9
−63.7
−108.4
−23.4
−62.6
−53.8
−40.1
−65.2
−56.0
−53.8
−56.9
−60.9
−29.7
8.1
−11.3
−57.7
−59.7
571.2∗
631.7∗∗
510.0∗∗
623.4∗∗
523.9∗∗
707.0∗∗
464.5
665.5∗
632.5∗
604.5
1109.2
665.8
834.8
1004.4
1036.0
576.3
608.3
641.7
689.8∗
1070.2
28
28
25
25
28
25
24
28
25
28
27
25
24
28
20
28
28
28
24
24
CMED
Kahramanmaraş
Gaziantep
Kilis
Malatya
Elazıǧ
Adıyaman
Şanlıurfa
Siverek
+0.14
−0.02
−0.02
−0.01
−0.03
−0.02
−0.00
+0.07
22.1
−2.7
−3.3
−0.6
−2.8
−4.2
−0.6
9.6
739.2
547.9
518.5
383.1
418.8
761.4
468.3
564.9
22
22
23
23
23
22
22
23
717.1
550.6
521.8
383.7
421.6
765.6
468.9
555.3
−0.09
−0.04
+0.04
−0.18
−0.10
−0.03
+0.03
+0.01
−14.0
−4.8
5.4
−16.4
−10.5
−8.6
3.4
1.1
703.1
545.8
527.2
367.3
411.1
757.0
472.3
556.4
24
24
27
28
28
25
25
28
(continued overleaf )
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1780
M. TÜRKEŞ AND E. ERLAT
Table I. (Continued )
Region
Station
Negative NAO conditions
P
CNA
CA
p
n
Positive NAO conditions
CNA
CA
p
n
492.6
718.6
696.7
28
28
25
CMED
Diyarbakır
Siirt
Cizre
+0.05
+0.02
−0.05
5.8
3.2
−8.7
491.1
728.0
678.6
23
23
22
485.3
724.8
687.3
+0.06
−0.03
+0.05
7.3
−6.2
9.4
MEDT
Kütahya
Uşak
Burdur
Isparta
+0.50
+0.25
+0.24
+0.40
55.3
24.7
19.3
61.3
613.4∗∗
561.7
442.0
624.4∗
23
23
22
23
558.1
537
422.7
563.1
−0.47
−0.30
−0.26
−0.28
−51.8
−29.3
−20.8
−43.7
506.3∗∗
507.7∗
401.9
519.4∗
28
28
24
28
CCAN
Kastamonu
Merzifon
Şebinkarahisar
Amasya
Çorum
Yozgat
Sivas
Eskişehir
Ankara
Sivrihisar
Afyon
Kırşehir
Kayseri
Ilgın
Aksaray
Niǧde
Konya
Karaman
Ulukışla
+0.11
+0.16
−0.04
+0.24
−0.00
+0.18
+0.20
+0.25
+0.29
+0.17
+0.18
+0.48
−0.03
+0.29
+0.30
+0.31
+0.33
+0.12
+0.02
10.8
12.3
−4.0
18.8
−0.1
16.6
16.3
16.3
21.9
13.5
16.0
33.1
−2.0
24.6
19.7
21.5
25.7
8.5
1.2
479.1
409.5
566.2
445.9
420.5
591.2
442.1
388.9
410.4
410.4
447.5
413.3∗∗
376.7
463.1
361.2
357.8
348.5
345.7
338.5
23
23
23
23
23
21
23
23
23
23
23
23
22
23
22
23
23
23
22
468.3
397.2
570.2
427.1
420.6
574.6
425.8
372.6
388.5
396.9
431.5
380.2
378.7
438.5
341.5
336.3
322.8
337.2
337.3
−0.10
−0.32
−0.14
−0.39
−0.12
−0.24
−0.05
−0.15
−0.21
−0.02
−0.17
−0.13
−0.08
−0.29
−0.28
−0.26
−0.29
−0.01
−0.12
−10.1
−24.5
−13.9
−30.0
−8.7
−22.1
−3.9
−9.9
−16.3
−1.2
−16.0
−8.8
−5.9
−24.4
−18.4
−18.1
−22.7
−0.7
−7.9
458.2
372.7∗
556.3
397.1∗
411.9
552.5
421.9
362.7
372.2
395.7
415.5
371.4
372.8
414.1∗
323.1
318.2
300.1∗
336.5
329.4
28
28
28
25
28
24
28
28
28
28
28
28
25
28
25
26
28
28
25
CEAN
Ardahan
Kars
Sarıkamış
Iǧdır
Bayburt
Erzurum
Erzincan
Hınıs
Van
−0.17
−0.14
+0.12
−0.17
+0.23
−0.10
+0.14
+0.04
+0.01
−17.8
−13.3
12.6
−11.6
21.3
−11.1
13.0
6.0
0.8
497.3
477.1
593.3
237.8
452.3
423.1
390.0
595.3
382.4
22
23
23
22
23
23
22
22
23
515.1
490.4
580.7
249.4
431
434.2
377
589.3
381.6
+0.10
+0.05
+0.00
+0.10
−0.18
−0.15
−0.22
−0.13
−0.01
10.5
5.1
0.3
7.0
−16.3
−16.4
−20.0
−17.0
−0.4
525.6
495.5
581.0
256.4
414.7
417.8
357.0
572.3
381.2
25
28
27
24
28
28
25
25
27
∗:
significant at the 0.05 level;
∗∗
: significant at the 0.01 level.
are considerably different from our results. However, their results for the western and southwestern regions
of Turkey, which are characterized by a Mediterranean-type climate and precipitation regime, have shown
a good agreement with our results, i.e. increased (decreased) precipitation conditions linked to the negative
(positive) NAOI phase. The similarity of the two studies concerning the Turkish precipitation responses to the
impacts of the NAO variability in the winter season is most evident during the positive NAOI phase. In fact,
it can be seen clearly that Cullen et al. (2002) computed the composite precipitation anomalies and the high
and low NAOI values by using a very short monthly precipitation data set with a 21 year record length and
an NAOI series with a 20 year length of record respectively. They also defined the high and low NAO index
values using a different approach, i.e. as the highest and the lowest quartiles in the 20 year record for each
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1781
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
32°
28°
40°
36°
BLACK
44°
SEA
Sea of
Marmara
40°
AEGEAN
SEA
40°
36°
36°
(a) Correlation coefficients
between the winter NAO index
and the normalized precipitation
MEDITERRANEAN SEA
0
50 100 150 200 250
km
32°
28°
28°
32°
0.49
0.39
SEA
0.43
0.58
0.66
0.38
0.47
AEGEAN
0.40
0.35
0.50
0.26
0.24
0.19
0.48
0.40
0.24
0.07
0.23
36°
(b) Composite winter
precipitation anomalies for the
negative NAO winter index phase
M E D IT E R R A N E A N S E A
50 100 150 200 250
km
-0.28
32°
-0.39
-0.38
SEA
-0.48
-0.29
-0.37
-0.39
-0.32
-0.45
-0.23
-0.31 -0.34
-0.23 -0.22
-0.45
AEGEAN
-0.24
-0.09
-0.19
-0.45
-0.26
-0.34
-0.15
40°
-0.26
-0.44
-0.36
-0.50
-0.18
-0.24
-0.22
-0.34
-0.18
-0.27
-0.47 -0.32
-0.25
-0.33
-0.25
-0.39
36°
(c) Composite winter
precipitation anomalies for the
positive NAO winter index phase
MEDITERRANEAN SEA
50 100 150 200 250
km
32°
-0.41
-0.30
-0.42
-0.38
-0.14
-0.32
-0.27
-0.45
-0.30
-0.36
-0.25
-0.44
-0.30
-0.36 -0.42
28°
-0.17
-0.43
-0.10
0.01 -0.17
-0.28
36°
0
-0.21
-0.38
-0.21
-0.30
44°
SEA
-0.14
-0.22
-0.23 -0.33
-0.38
-0.32 -0.34
-0.30
-0.41
-0.28
44°
40°
-0.06
-0.27
Sea of
Marmara
40°
36°
BLACK
-0.43
-0.40
40°
36°
32°
-0.32
0.17
0.21
0.42
0.43
0.31
0.30
0.20
0.11
0.47
0.46
-0.02
0.15
28°
40°
0.11
0.29
0.22
0.35
28°
0.17
0.23
0.26
0.37
0.49
36°
0
0.29
0.30
0.41
0.45
0.46
0.34
0.25
0.23
-0.14 0.03
0.05
0.55
0.53
0.32
0.41
0.24
0.63
0.52
0.44
0.32
0.45
0.10
SEA
0.23
0.23
0.56
0.36
0.21
0.38 0.55
0.41
44°
0.44
0.46
0.22
44°
40°
-0.16
0.24
Sea of
Marmara
40°
36°
BLACK
0.380.54
0.49
0.53
40°
36°
36°
40°
44°
Figure 4. As for Figure 3, but for winter
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1782
M. TÜRKEŞ AND E. ERLAT
Table II. As for Table I, but for the winter precipitation of 78 stations in Turkey
Region
Station
Negative NAO conditions
CNA
CA
P
p
n
681.6
217.6
360.3
225.9
197.5
404.3
175.7
280.7
22
22
22
22
21
22
22
20
Positive NAO conditions
CNA
CA
676.4
229.5
355.7
209.6
207.4
385.0
165.9
265.3
−0.17
+0.01
−0.21
−0.14
−0.06
−0.27
−0.37
−0.29
−31.2
0.9
−20.8
−10.0
−3.7
−21.8
−17.2
−20.6
645.2
230.4
334.9
199.6
203.7
363.2
148.7∗
244.7
25
25
25
25
23
23
25
22
p
n
BLS
Rize
Trabzon
Giresun
Samsun
Sinop
Zonguldak
Bolu
Adapazarı
+0.03
−0.14
+0.05
+0.23
−0.16
+0.24
+0.21
+0.22
5.2
−11.9
4.6
16.3
−9.9
19.3
9.8
15.4
MRT
Göztepe
Lüleburgaz
Kırklareli
Edirne
Tekirdaǧ
Bilecik
Bursa
+0.46
+0.49
+0.54
+0.38
+0.53
+0.55
+0.38
36.0
40.7
44.2
26.1
39.5
27.0
29.8
303.0∗∗
237.9∗∗
225.7∗∗
207.1∗
246.0∗∗
170.4∗∗
292.8∗
22
18
22
22
22
22
22
267.0
197.2
181.5
181.0
206.5
143.4
263.0
−0.38
−0.43
−0.32
−0.28
−0.40
−0.34
−0.32
−29.8
−35.7
−25.6
−19.4
−30.2
−16.7
−25.3
237.2∗
161.5∗∗
155.9∗
161.6
176.3∗
126.7∗
237.7∗
25
22
24
25
24
25
25
MED
Çanakkale
Bandırma
Balıkesir
Edremit
Akhisar
Simav
Salihli
Manisa
İzmir
Aydın
Muǧla
Bodrum
Fethiye
Antalya
Alanya
Silifke
Mersin
Adana
İskenderun
Antakya
+0.39
+0.49
+0.41
+0.43
+0.44
+0.66
+0.45
+0.32
+0.10
+0.41
+0.35
+0.24
+0.25
+0.15
+0.19
+0.24
+0.24
+0.20
+0.48
+0.40
36.1
52.0
38.4
54.8
46.8
108.0
35.2
41.8
12.8
45.0
81.2
35.0
48.6
37.9
39.3
33.3
30.4
26.5
55.4
69.9
310.3∗
350.3∗∗
290.6∗
398.5∗
335.9∗
503.8∗∗
259.5∗
415.4
396.0
383.8∗
769.1∗
479.2
581.7
699.5
663.3
387.4
362.2
348.1
346.3∗
621.6∗
22
22
20
20
22
20
20
22
20
22
22
20
20
22
17
22
22
22
20
20
274.2
298.3
252.2
343.7
289.1
395.8
224.3
373.6
383.2
338.8
687.9
444.2
533.1
661.6
624.0
354.1
331.8
321.6
290.9
551.7
−0.38
−0.39
−0.41
−0.48
−0.32
−0.45
−0.22
−0.23
−0.23
−0.30
−0.42
−0.36
−0.18
−0.36
−0.22
−0.34
−0.14
−0.18
−0.47
−0.39
−35.2
−41.4
−38.4
−61.7
−33.7
−73.2
−16.8
−30.7
−28.6
−32.6
−96.1
−54.0
−35.2
−89.1
−46.3
−46.4
−17.3
−24.0
−53.6
−68.8
239.0∗
256.9∗
213.8∗
282.0∗∗
255.4∗
322.6∗∗
207.5
342.9
354.6
306.2
591.8∗∗
390.2∗
497.9
572.5∗
577.7
307.7∗
314.5
297.6
237.3∗∗
482.9∗
25
24
22
22
25
22
22
25
22
25
25
22
22
24
17
25
25
25
22
22
CMED
Kahramanmaraş
Gaziantep
Kilis
Malatya
Elazıǧ
Adıyaman
Şanlıurfa
Siverek
Diyarbakır
Siirt
Cizre
+0.50
+0.31
+0.30
+0.46
+0.47
+0.43
+0.23
+0.42
+0.21
+0.17
+0.07
54.0
24.3
25.5
16.6
20.2
60.6
19.0
35.2
14.3
18.3
9.4
428.6∗∗
300.6
295.5
139.4∗∗
152.4∗∗
465.7∗
267.6
290.4∗
225.0
311.0
356.3
20
20
21
22
22
20
20
22
22
22
20
374.6
276.3
270.0
122.8
132.2
405.1
248.6
255.2
210.7
292.7
346.9
−0.42
−0.27
−0.32
−0.27
−0.25
−0.24
−0.25
−0.41
−0.30
−0.25
−0.33
−44.8
−21.6
−27.7
−9.7
−10.6
−34.5
−20.5
−34.8
−20.0
−26.9
−41.4
329.8∗
254.7
242.3∗
113.1
121.6
370.6
228.1
220.4∗
190.7
265.8
305.5∗
22
22
23
25
24
22
22
25
25
25
22
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1783
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
Table II. (Continued )
Region
Station
Negative NAO conditions
CNA
CA
p
P
n
Positive NAO conditions
CNA
CA
p
n
MEDT
Kütahya
Uşak
Burdur
Isparta
+0.58
+0.47
+0.46
+0.34
47.9
36.8
29.9
38.3
262.0∗∗
258.5∗∗
194.7∗
278.1
22
22
20
22
214.1
221.7
164.8
239.8
−0.39
−0.31
−0.50
−0.36
−32.5
−23.9
−32.1
−40.1
181.6∗
197.8
132.7∗∗
199.7∗
25
25
22
25
CCAN
Kastamonu
Merzifon
Şebinkarahisar
Amasya
Çorum
Yozgat
Sivas
Eskişehir
Ankara
Sivrihisar
Afyon
Kırşehir
Kayseri
Ilgın
Aksaray
Niǧde
Konya
Karaman
Ulukışla
+0.44
+0.23
+0.36
+0.56
+0.35
+0.40
+0.55
+0.52
+0.64
+0.53
+0.38
+0.45
+0.37
+0.32
+0.49
+0.29
+0.22
−0.02
+0.26
13.8
7.4
16.9
24.6
13.2
24.9
21.9
23.9
27.2
23.0
17.9
18.0
12.1
14.2
13.8
9.9
9.8
−1.0
10.7
104.5∗
110.7
169.8∗
161.3∗∗
125.5∗
234.4∗
148.8∗∗
147.9∗∗
148.0∗∗
152.4∗∗
146.9∗
154.8∗∗
119.1∗
144.2
131.6∗∗
118.6
117.9
128.3
112.2
22
22
22
20
22
18
22
22
22
22
22
22
20
22
20
21
22
22
20
90.7
103.3
152.9
136.7
112.3
209.5
126.9
124.0
120.8
129.4
129.0
136.8
107.0
130.0
117.8
108.7
108.1
129.3
101.5
−0.28
−0.22
−0.17
−0.33
−0.23
−0.24
−0.43
−0.30
−0.45
−0.38
−0.34
−0.28
−0.44
−0.21
−0.44
−0.45
−0.30
−0.30
−0.38
−8.7
−7.2
−8.1
−14.5
−8.6
−14.9
−17.1
−13.8
−19.5
−16.6
−15.8
−11.0
−14.4
−9.2
−12.4
−15.5
−13.7
−12.8
−15.8
82.0
96.1
144.8
122.2∗
103.7
194.6
109.8∗∗
110.2
101.3∗∗
112.8∗
113.2∗
125.8
92.6∗∗
120.8
105.4∗∗
93.2∗∗
94.4
116.5
85.7∗
24
25
25
22
25
22
25
25
25
25
25
24
22
25
22
22
25
25
22
CEAN
Ardahan
Kars
Sarıkamış
Iǧdır
Bayburt
Erzurum
Erzincan
Hınıs
Van
+0.23
+0.29
+0.30
+0.17
+0.41
+0.23
+0.26
+0.11
+0.11
5.6
7.4
10.9
3.06
11.5
7.5
9.9
7.6
4.0
66.1
77.9
123.1
49.0
94.0∗
81.9
100.4
183.6
108.6
20
22
22
20
22
22
20
20
21
60.5
70.5
112.2
46.0
82.5
74.4
90.5
176.0
104.6
−0.10
−0.09
−0.19
−0.26
−0.45
−0.34
−0.15
−0.26
−0.32
−2.4
−2.3
−6.8
−4.6
−12.8
−11.1
−5.8
−17.4
−11.6
58.1
68.2
105.4
41.4
69.7∗∗
63.3∗
84.7
158.6
93.0∗
22
25
24
22
24
24
22
22
23
∗:
significant at the 0.05 level;
∗∗
: significant at the 0.01 level.
month, and computed composite precipitation anomalies for the months from December to March (the DJFM
winter). Consequently, the apparent inconsistency of some results detected by Cullen et al. (2002) with some
results of our study may have arisen from these significant differences in computing methods of the extreme
NAOI anomaly phases and the corresponding composite precipitation anomalies, along with the very short
study period they used.
Composite precipitation anomalies on the coastal area of the Black Sea region, particularly in winter, are
clearly distinct from the other regions of Turkey, in particular with respect to the magnitude of the precipitation
responses to the extreme NAOI phases. For instance, winter dry signals occurring during the positive winter
NAOI phase are seen in all rainfall regions of Turkey apart from the BLS. In fact, according to various studies
dealing with Turkey’s precipitation climatology, observed precipitation changes and variability, relationships
with the variations of the SLP and the higher atmospheric conditions, and the links to the atmospheric
circulation indices (e.g. Kutiel et al., 2001; Türkeş, 1996a, 1998a,b, 2000; Türkeş et al., 2002), the BLS
region differs considerably from the other regions of Turkey in terms of high precipitation totals, a temperate
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1784
M. TÜRKEŞ AND E. ERLAT
rainy climate and low interannual variability, orographic precipitation occurrence and being affected by the
rain-bearing weather circulation types during the year, etc.
The unique conditions of the BLS precipitation responses to the year-to-year variability and the extreme
phases of the NAO can be attributed to, and/or explained by, the following synoptic-scale atmospheric
control mechanisms and the physical geographic conditions dominating the rainfall occurrence of the region.
Mediterranean-originated frontal depressions generally affect the BLS region in late autumn and winter,
whereas the northeastern Atlantic-originated (Icelandic) frontal depressions with a northerly circulation are
more effective over the region almost throughout the year, by the orographic enhancement process. Icelandic
frontal depressions and northerly sector air-streams from ridges of high pressure behind these frontal systems
bring heavy precipitation to the region throughout the year, particularly in autumn and winter. In addition to the
direct effects of the frontal systems in all seasons, the northwestern and the northeastern coastal areas bordering
the Black Sea obtain precipitation from the northerly air-flows associated with the post-frontal ridging highpressure cells, or when storm tracks lie anomalously to the south, producing onshore flow there (Türkeş,
1998a,b). Orographic effects of the windward slopes of the Northern Anatolia Mountains also contribute
continuously to increased rainfall occurrence over the region. Consequently, seasonal precipitation totals
show a highly homogeneous distribution during the year, although the regional effects of these atmospheric
forces are weaker in late spring and summer.
The results strongly depict the existence of a perfect similarity between the magnitude and the spatial
distribution patterns of the significant precipitation anomalies and of the significant CCs, and between the
small anomalies and the non-significant CCs. This close similarity between the magnitude and the spatial
coherence of the precipitation anomalies and of the CCs verifies our results on the precipitation responses
and the signals in Turkey.
3.3. Spring NAOI responses
Relationships between the interannual variations of the spring precipitation anomalies and the spring NAOI
are mostly characterized by a negative correlation in Turkey, except for 13 stations. CCs, however, are
significant only at the eight stations of the BLS and MRT regions (Figure 5(a)). The spring NAOI responses
are weaker than those appearing in winter and autumn seasons, which are in harmony with our expectations
based on the correlation analysis.
Spring precipitation corresponding to the negative NAOI phase tended to increase at 55 stations in
comparison with the long-term average (Figure 5(b)). Nevertheless, wetter than long-term average conditions
are significant only at the stations of Kırklareli in the northern MRT and Trabzon and Samsun on the Black Sea
coast. For the positive NAOI phase, drier than long-term average conditions are significant at nine stations,
although composite precipitation anomalies are mostly negative in Turkey, except at some stations of the
CMED, CCAN and CEAN regions (Figure 5(c)).
3.4. Summer NAOI responses
In Turkey, CCs between the precipitation and the NAO are weakest in summer. In this season, the
frequency of the mid-latitude frontal depressions reaching the eastern Mediterranean basin, including the
region of Turkey, is drastically decreased and the average precipitation totals are about 50–60 mm over
most the country, except for the BLS, the MRT and the northeastern Anatolia regions (Türkeş, 1998a). The
average precipitation totals are even below 5 mm in the southern margin of the CMED region. In summer,
local and/or sub-regional conditions are also effective, as much as the prevailing large-scale atmospheric
control mechanisms. Consequently, the weak negative and positive CCs depict a complex distribution pattern
(Figure 6(a)).
The negative NAOI responses of 46 stations are defined by a composite positive precipitation anomaly
(Figure 6(b)). However, the majority of the wetter than long-term average precipitation conditions, except for
the stations of Fethiye and Şanlıurfa/Siverek in the southwest and the southeast of Anatolian Peninsula
respectively, are not significant. The clear opposition determined between the signs of the composite
precipitation anomalies and the extreme NAOI anomaly phases for other seasons almost disappears in summer.
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1785
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
28°
32°
40°
36°
BLACK
44°
SEA
Sea of
Marmara
40°
AEGEAN
SEA
40°
36°
36°
(a) Correlation coefficients between
the spring NAO index and the
normalized precipitation
MEDITERRANEAN SEA
0
50 150 100 200 250
km
28°
32°
28°
32°
0.33
SEA
0.02
0.15
0.37
0.18
0.34
0.01
0.26
0.19
-0.12
AEGEAN
-0.05
-0.09
0.04
0.11
0.15
0.12
0.09
0.05
0.02
-0.23
-0.08
0.11
-0.21
0.16
36°
(b) Composite spring precipitation
anomalies for the negative NAO
spring index phase
M E D I T E R R A N EA N S E A
50 150 100 200 250
km
32°
28°
SEA
-0.17
-0.11
-0.16
-0.18
-0.38
-0.35
-0.41 -0.22
AEGEAN
40°
-0.07
-0.20
0.01
-0.17
-0.24
-0.13
-0.180.00
-0.34
0.05
-0.27
0.00
-0.19
-0.01
-0.19
0.06
-0.02
-0.07
-0.38
0.06
0.30
0.23
0.25
-0.01
36°
(c) Composite spring precipitation
anomalies for the positive NAO
spring index phase
50 150 100 200 250
km
32°
-0.28
-0.18
-0.30
0.38
-0.16
-0.11
M E D IT E R R A N E A N S E A
28°
0.33
0.02
-0.16
36°
0
0.01
-0.11
-0.24
-0.44
-0.44
-0.24
-0.14
-0.27
-0.35
-0.03
-0.50 -0.09
-0.40
-0.33
-0.33
-0.26
-0.15 -0.28
-0.25
-0.26
-0.33 -0.41
-0.18
44°
SEA
-0.23
-0.44
-0.20 -0.31
-0.41
44°
40°
-0.12
-0.08
-0.12
40°
36°
BLACK
-0.20
-0.33
40°
36°
32°
Sea of
Marmara
-0.12
-0.22
-0.08
0.04
0.13
0.07
0.07
0.12
-0.24
40°
0.18
-0.06
-0.10
0.22
-0.09
-0.18
-0.25 -0.44
-0.07
0.15
-0.06
0.06
0.11
-0.10
0.09
28°
0.01
0.07
0.12
-0.03
36°
0
-0.08
0.18
0.22
0.34
-0.07
0.29
0.14
-0.04
0.03
-0.06 0.01
44°
0.47
0.31
-0.11
0.22
0.23
0.25
0.13 0.00
40°
0.55
0.04
0.32
0.02
0.33
Sea of
Marmara
44°
SEA
0.06
0.23
-0.10
40°
36°
BLACK
0.310.41
-0.13
40°
36°
36°
40°
44°
Figure 5. As for Figure 3, but for spring
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1786
M. TÜRKEŞ AND E. ERLAT
28°
32°
36°
BLACK
40°
44°
SEA
Sea of
Marmara
40°
AEGEAN
SEA
40°
36°
36°
(a) Correlation coefficients
between the summer NAO index
and the normalized precipitation
M E D I TE R R A N E A N S E A
0
50 100 150 200 250
km
28°
28°
32˚
SEA
AEGEAN
0.09
-0.16
-0.01
40°
-0.06
-0.12
-0.13
-0.00
50 100 150 200 250
32°
28°
0.08
SEA
0.17
0.35
0.38
-0.030.29
-0.18
0.26
0.31
0.20 0.21
0.01
-0.11
0.12
0.16
-0.06
-0.27
0.11
-0.06
0.29
0.36 0.33
0.23
MEDITERRANEAN SEA
28°
40°
0.20
0.03 -0.06
0.16
0.14
0.22
0.11
36°
(c) Composite summer precipitation
anomalies for the positive NAO
summer index phase
km
32°
0.39
0.18
0.21
0.20
-0.11
-0.11
50 100 150 200 250
0.10
0.27
0.12
0.33
0.32
36°
0
0.31
0.27
0.22
0.21
-0.01
-0.14
-0.18
-0.29
0.05
0.32 -0.00
0.03
0.18
-0.07
0.12
0.06
0.11 0.17
44°
SEA
0.00
0.19
0.11 0.21
0.02
-0.07 0.23
0.15 0.04
AEGEAN
0.15
-0.11
0.07
36°
44°
40°
-0.29
0.00
Sea of
Marmara
40°
36°
BLACK
0.12
-0.00
36°
32°
0.300.14
0.36
40°
(b) Composite summer precipitation
anomalies for the negative NAO
summer index phase
km
28°
40°
-0.20
0.22 0.33
0.22
MEDITERRANEAN SEA
0
44°
-0.09
0.22
0.19
-0.09
-0.17
0.18
0.02
0.43 0.02
0.04
0.19
-0.14
-0.06
0.14
0.07
0.35
-0.34
-0.28 0.08
0.29
-0.13
-0.15 -0.02
-0.03
-0.06
0.06
0.23
-0.15
0.18
0.15
0.02
0.21
0.14
0.18
0.38
0.16
-0.01
0.25 0.44
-0.14
0.15
0.31
-0.03
-0.32 0.05
0.14
-0.15 0.64
0.11
-0.16
0.15
0.46
-0.26 0.17
0.17
0.07
0.26
0.03 -0.02
0.12
36°
0.07
44°
SEA
0.02
0.12
Sea of
Marmara
40°
36°
BLACK
-0.21-0.09
-0.07
0.10
40°
36°
32°
36˚
40°
44°
Figure 6. As for Figure 3, but for summer
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
1787
Composite precipitation anomalies corresponding to the positive summer NAOI phase are characterized by a
positive anomaly at 58 stations (Figure 6(c)). Increased composite summer precipitation is significant only at
the stations of Lüleburgaz, Akhisar, İskenderun, Eskişehir and Van, all of which are distributed over different
regions of Turkey and show no spatial coherence or geographical relationship.
3.5. Autumn NAOI responses
There is a negative relationship between the autumn precipitation anomalies and the autumn NAOI
anomalies at most stations in Turkey except some over the Mediterranean coastal belt and the northeastern
Anatolia sub-region, and particularly in the CMED region (Figure 7(a)). Negative CCs are statistically
significant at 23 stations, 15 of which are at the 0.01 level. Stations with a significant CC show a
spatial coherence over the southern Marmara, northwestern MED, the MEDT and the mid CCAN regions
(Figure 7(a)).
Autumn NAOI responses are weaker than those in winter precipitation and greater than those in spring
and summer precipitation. Composite precipitation anomalies during the negative NAOI phase are found to
be positive at 69 stations of Turkey, except for some stations mainly located in the southern CMED and the
eastern CEAN regions (Table III; Figure 7(b)). Composite precipitation means that are wetter than long-term
average are significant at 22 stations. Wet signals are evident mostly in the MRT, MEDT and MED regions, and
the middle and northeastern parts of the CCAN region (Table III; Figure 7(b)). Autumn precipitation tended
to decrease during the positive autumn NAOI phase over most of Turkey, except for 16 stations located
mainly in the CMED region and the northeastern part of the Anatolian Peninsula (Figure 7(c)). Significant
dry conditions show up at 21 stations.
In autumn, it is also evident that an area of significant negative CC indicates a perfect agreement with the
coherent regions with the extreme NAOI signals, as in the winter and annual patterns.
3.6. Individual yearly and longer time-scale NAOI responses
Some examples for individual yearly and longer time-scale changes in winter and annual precipitation in
Turkey that are found to have been controlled by year-to-year and quasi-decadal variability of the NAO are
given for the period 1960–2000 by considering persistent extreme NAOI periods and individual extreme
NAOI years.
Over the past about 135 years, the NAO has shown considerable variability at the quasi-biennial and quasidecadal and/or decadal time scales. High-frequency oscillations in the NAOI were observed during the last
35 years of the 19th century, whereas low-frequency fluctuations were particularly pronounced for a long
period in the second half of the 20th century (Figure 1). In winter, quasi-decadal and decadal time-scale
low-frequency fluctuations were also dominant in the upper atmospheric conditions (i.e., 700 and 500 hPa
geopotential heights) over Turkey (Türkeş, 1998a; Türkeş et al., 2002). Türkeş et al. (2002) reported that
long cycles of 8.4, 12–12.7, 14, 18 and 21 years in the winter precipitation series were evident, particularly
at stations of the MRT and Mediterranean rainfall regions.
The NAO tended mostly to show a low-index phase during the period lasting from about the early 1950s
to the very early 1970s, and a high-index phase during the period from 1972 to the late 1990s (Figure 1). The
low-frequency fluctuations in the circulation over the Atlantic region have been closely linked to coherent
large-scale precipitation anomalies that have persisted, particularly in winter, over Turkey since the early
1960s. This period includes the following marked anomaly periods: wet conditions in the 1960s and the late
1970s, and dry conditions in the early–mid 1970s, the late 1980s and early–mid 1990s and in the late 1990s
(Türkeş, 1996a–c, 1998a, 2003).
Annual and particularly winter precipitation totals increased over most of Turkey during the negative
NAOI period 1963–69, with the exception of the year 1967 (Figure 8(a) and 8(b)). For instance, composite
winter precipitation means for the negative NAOI period of 1963–69 with a mean anomaly of −2.92 are
significantly above the long-term average at 35 stations in Turkey (Figure 8(b)). Wet signals are seen over all
regions of Turkey, except in the eastern Black Sea and the northeastern Anatolia sub-regions characterized
by below-average conditions.
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1788
M. TÜRKEŞ AND E. ERLAT
32°
28°
36°
40°
BLACK
44°
SEA
Sea of
Marmara
40°
AEGEAN
SEA
40°
36°
36°
(a) Correlation coefficients
between the autumn NAO index
and the normalized precipitation
M E D IT E R R A N E A N S E A
0
50 100 150 200 250
km
28°
32°
28°
32°
0.64
0.28
0.62
SEA
0.35
0.24
0.36
0.29
0.57
0.46
0.43
0.54
0.43
0.30
0.07 0.34
0.44
AEGEAN
0.15
0.19
0.20
0.20
0.01
-0.00
0.34
0.05
0.52
0.11
-0.03
0.01
0.20
0.08
0.24
-0.08
0.43
36°
(b) Composite autumn precipitation
anomalies for the negative NAO
autumn index phase
32°
SEA
-0.29
-0.26
-0.16
-0.42
-0.32
-0.50
-0.32
-0.37 -0.35
-0.36
-0.30
-0.19 -0.40
AEGEAN
-0.13
0.02
-0.28
40°
-0.20
-0.26
0.01
-0.28
0.11
-0.09
0.02
-0.16
-0.14
-0.17
-0.19
0.01
0.12
-0.05 0.09
0.09
0.02
-0.01
0.01
-0.22
36°
(c) Composite autumn precipitation
anomalies for the positive NAO
autumn index phase
M E D IT E R R A N E A N S E A
50 100 150 200 250
km
32°
0.13
-0.47
-0.36
0.10
28°
-0.00
0.08
-0.19
-0.29
-0.27
-0.01
-0.06
0.11
0.02
-0.12
-0.43
36°
0
-0.16
-0.04
-0.28
-0.05
-0.60
-0.28
-0.10
-0.15 -0.11
-0.28
-0.40 -0.37
-0.39
44°
SEA
0.01
-0.29
-0.37 -0.46
-0.30
-0.37
-0.22
-0.47
44°
40°
-0.04
-0.06
Sea of
Marmara
40°
36°
BLACK
-0.19
40°
36°
32°
-0.12
-0.06
-0.07
-0.20
50 100 150 200 250
km
28°
-0.13
-0.08
-0.02
M E D IT E R R A N E A N S E A
28°
-0.06
0.03
0.32
0.49
36°
0
40°
0.01
0.35
0.13
0.54
0.41
-0.05
0.34
0.31
0.48
0.44
0.17
-0.01
0.20
0.44
0.27
0.32
0.30
0.08 0.12
0.38
0.38 0.22
0.62
0.21
0.31
0.50
0.47 0.49
0.37
44°
SEA
0.37
0.52
Sea of
Marmara
44°
40°
0.31
0.00
0.41
40°
36°
BLACK
0.05 0.16
0.09
40°
36°
36°
40°
44°
Figure 7. As for Figure 3, but for autumn
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1789
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
Table III. As for Table I, but for the autumn precipitation of 78 stations in Turkey
Region
Station
Negative NAO conditions
P
CNA
CA
p
n
Positive NAO conditions
CNA
CA
p
n
BLS
Rize
Trabzon
Giresun
Samsun
Sinop
Zonguldak
Bolu
Adapazarı
+0.12
+0.08
+0.38
+0.31
+0.31
+0.00
+0.37
+0.35
22.3
5.9
40.0
22.2
26.0
0.1
13.1
28.0
817.5
290.4
469.6
241.4
251.1
396.6
128.2
240.0
19
19
19
19
19
19
19
18
795.2
284.5
429.6
219.2
225.1
396.5
115.1
212.0
−0.11
−0.15
−0.28
+0.01
−0.04
−0.06
−0.16
−0.26
−21.3
−11.2
−28.6
0.5
−2.9
−8.0
−5.6
−20.6
773.9
273.3
400.4
219.7
222.2
388.5
109.5
191.4
26
26
26
26
26
26
26
22
MRT
Göztepe
Lüleburgaz
Kırklareli
Edirne
Tekirdaǧ
Bilecik
Bursa
Çanakkale
Bandırma
Balıkesir
+0.52
+0.09
+0.18
+0.05
+0.41
+0.22
+0.39
+0.28
+0.64
+0.62
34.3
5.9
10.5
3.6
27.7
8.7
23.8
18.8
56.1
35.6
234.0∗
169.1
157.0
162.3
191.3∗
103.4
203.1
176.0
245.5∗∗
173.7∗∗
19
16
19
19
19
19
19
19
19
18
199.7
163.2
146.5
158.7
163.6
94.7
179.3
157.2
189.4
138.1
−0.30
−0.06
−0.12
−0.08
−0.19
−0.37
−0.40
−0.22
−0.37
−0.39
−20.0
−3.7
−7.1
−5.4
−12.6
−14.7
−24.6
−14.9
−32.2
−22.5
179.7∗
159.5
139.4
153.3
151.0
80.0∗
154.7∗
142.3
157.2∗
115.6∗
26
20
26
26
26
26
26
26
26
22
MED
Edremit
Akhisar
Simav
Salihli
Manisa
İzmir
Aydın
Muǧla
Bodrum
Fethiye
Antalya
Alanya
Silifke
Mersin
Adana
İskenderun
Antakya
+0.62
+0.43
+0.46
+0.34
+0.30
+0.07
+0.17
+0.41
+0.21
+0.34
−0.00
+0.52
+0.08
+0.05
+0.01
+0.20
+0.43
62.2
27.2
32.0
18.2
20.7
5.2
10.4
38.3
17.1
33.7
−0.1
78.6
7.3
4.9
1.2
16.7
45.9
244.4∗∗
152.2∗
198.1∗
120.0
173.7
145.9
143.5
250.0∗
167.7
230.5
210.8
340.1∗
142.1
135.0
136.5
220.0
260.9∗
17
19
17
16
19
17
19
19
18
17
19
13
19
19
19
17
17
182.2
125.0
166.1
101.8
153.0
140.7
133.1
211.7
150.6
196.8
210.9
261.5
134.8
130.1
135.3
203.3
215.0
−0.29
−0.36
−0.32
−0.40
−0.30
−0.19
−0.13
−0.01
−0.05
−0.06
+0.10
−0.28
+0.11
+0.01
−0.17
−0.19
−0.22
−28.7
−22.8
−22.2
−21.5
−20.8
−13.2
−8.0
−0.7
−4.0
−6.0
14.9
−41.6
10.2
0.6
−13.9
−15.5
−24.1
153.5
102.2∗
143.9∗
80.3∗
132.2∗
127.5
125.1
211.0
146.6
190.8
225.8
219.9
145.0
130.7
121.4
187.8
190.9
22
26
22
21
26
22
26
26
22
21
26
17
26
26
26
21
21
CMED
Kahramanmaraş
Gaziantep
Kilis
Malatya
Elazıǧ
Adıyaman
Şanlıurfa
Siverek
Diyarbakır
Siirt
Cizre
+0.20
+0.11
−0.03
+0.15
+0.03
+0.24
−0.02
−0.07
−0.08
−0.13
−0.21
14.5
6.1
−1.6
6.9
1.3
15.9
−1.0
−4.0
−4.1
−10.0
−13.5
144.3
108.7
93.9
91.7
99.7
133.8
71.3
97.8
83.5
126.0
81.1
17
17
19
19
19
17
18
19
19
19
17
129.8
102.6
95.5
84.8
98.4
117.9
72.3
101.8
87.6
136.0
94.6
−0.16
+0.01
+0.12
+0.02
+0.13
−0.05
+0.01
+0.09
+0.09
+0.02
−0.01
−11.8
0.8
6.6
0.8
7.1
−3.2
0.5
5.5
4.2
1.8
−0.4
118.0
103.4
102.1
85.6
105.5
114.7
72.8
107.3
91.8
137.8
94.2
21
21
26
26
26
22
22
26
26
26
22
(continued overleaf )
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
1790
M. TÜRKEŞ AND E. ERLAT
Table III. (Continued )
Region
Station
Negative NAO conditions
CNA
CA
p
P
n
Positive NAO conditions
CNA
CA
p
n
MEDT
Kütahya
Uşak
Burdur
Isparta
+0.57
+0.54
+0.54
+0.13
26.0
24.4
18.8
6.4
135.2∗∗
134.5∗
99.8∗
102.6
19
19
17
19
109.2
110.1
81.0
96.2
−0.50
−0.37
−0.28
+0.02
−22.6
−16.6
−9.7
1.0
86.6∗∗
93.5∗
71.3
97.2
26
26
21
26
CCAN
Kastamonu
Merzifon
Şebinkarahisar
Amasya
Çorum
Yozgat
Sivas
Eskişehir
Ankara
Sivrihisar
Afyon
Kırşehir
Kayseri
Ilgın
Aksaray
Niǧde
Konya
Karaman
Ulukışla
+0.37
+0.51
+0.24
+0.49
+0.47
+0.45
+0.27
+0.29
+0.36
+0.32
+0.43
+0.48
+0.35
+0.44
+0.32
+0.19
+0.49
+0.01
+0.20
12.4
17.6
13.7
21.4
15.7
24.7
11.9
8.6
12.4
10.3
13.9
18.6
12.5
18.5
10.0
5.7
20.8
0.3
5.8
103.8
96.6∗
148.3
108.8∗
95.4∗
129.8∗
100.4
81.4
87.4
87.2
97.2∗
89.7∗
85.8
113.4∗
73.0
68.3
92.7∗
67.5
65.7
19
19
19
18
19
16
19
19
19
19
19
19
18
19
17
18
19
19
18
91.4
79.0
134.6
87.4
79.7
105.1
88.5
72.8
75.0
76.9
83.3
71.1
73.3
94.9
63.0
62.6
71.9
67.2
59.9
−0.47
−0.29
−0.16
−0.46
−0.37
−0.60
−0.29
−0.33
−0.42
−0.28
−0.36
−0.43
−0.27
−0.28
−0.47
−0.20
−0.38
−0.26
−0.15
−16.0
−10.1
−9.1
−20.1
−12.1
−33.1
−12.5
−9.6
−14.5
−9.1
−11.5
−16.4
−9.5
−12.0
−14.7
−6.1
−16.1
−9.3
−4.3
75.4∗∗
68.9
125.5
67.3∗∗
67.6∗
72.0∗∗
76.0
63.2∗
60.5∗∗
67.8
71.8∗
54.7∗∗
63.8
82.9
48.3∗∗
56.5
55.8∗
57.9
55.6
26
26
26
23
26
20
26
26
26
26
26
26
22
26
22
24
26
26
22
CEAN
Ardahan
Kars
Sarıkamış
Iǧdır
Bayburt
Erzurum
Erzincan
Hınıs
Van
+0.30
−0.02
+0.20
−0.05
+0.44
+0.34
+0.31
+0.01
−0.06
9.8
−0.6
9.0
−1.5
17.8
15.0
13.3
0.8
−2.7
105.0
93.2
129.4
52.9
114.5∗
120.8
105.7
128.1
101.1
17
19
19
17
19
19
18
17
19
95.2
93.8
120.4
54.4
96.7
105.8
92.4
127.3
103.8
−0.10
+0.11
+0.02
0.00
−0.12
+0.08
−0.20
−0.04
−0.09
−3.3
4.5
0.8
0.0
−5.0
3.5
−8.6
−2.5
−4.0
91.9
98.3
121.2
54.4
91.7
109.3
83.8
124.8
99.8
22
26
26
21
26
26
22
22
26
∗:
significant at the 0.05 level;
∗∗
: significant at the 0.01 level.
On the other hand, annual and particularly winter precipitation decreased at the majority of the stations
during the positive NAOI period of 1989–94 (Figure 8(c) and 8(d)). Composite annual negative anomalies
corresponding to the positive NAOI period of 1989–94 with a mean anomaly of +2.42 show a large spatial
coherence over most of Turkey. Drier than long-term average annual precipitation conditions are significant
at 18 stations, mostly distributed over the MRT and the MED regions, and the western and southern parts of
the CCAN region. Significantly drier than long-term average precipitation conditions are much more evident
for the positive NAOI winter period of 1989–94, with a mean anomaly of +1.85, with respect to both the
large-scale spatial coherence and the magnitudes of the anomalies. In winter, dry conditions are significant
at 29 stations. The dry signals show up over all rainfall regions, except for the large eastern region of the
Anatolian Peninsula, including the CEAN as a whole.
Marked wet conditions and meteorological drought events over Turkey in the individual years are also
controlled by the extreme low and high index NAO anomaly years. By considering the extreme NAOI
anomaly years for the period 1960–2000, it is found that large-scale severe drought events, e.g. in the winters
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
0
0
0.86
0.61
0.35
0.60
1.17
0.91
1.19
28°
50 100 150 200 250
km
0.60
0.42
1.01
0.97
0.17
0.39
0.44
0.17
0.51
0.88
0.18
0.89
0.98
0.95 0.45
0.71
36°
0.79
0.33
SEA
0.42
0.18
0.36
0.34
0.69
0.77
0.62
36°
0. 72
0.51
0.60
0.99 0.47
0.58
36°
0.72
1.07
0.89
0.97
0.63
1.27
0.81
0.42
0.93
0.41
32°
SEA
0.34
0.87
0.88
0.76
0.94 0.61
0.94
MEDITERRANEAN
0.16 0.76
0.39
0.63
0.92
0.35 0.74
1.03
1.38
Sea of
Marmara
1.28
32°
BLACK
32°
0.15
0.46
0.16
0.18
SEA
0.28
0.14
-0.21
-0.29 -0.17
0.63
0.81
36°
0.32
0.29
0.64
0.31
0.50
1.00
0.70
0.26
0.92
28°
km
SEA
0.58
1.17
0.79
0.87
1.07
0.94 -0.03
-0.33
0.12
0.941.08
1.33
28°
50 100 150 200 250
-0.03
0.14 0.33
0.97
MEDITERRANEAN
0.32 0.43
0.16
0.32
0.81
0.25 0.79
0.63
0.70
Sea of
Marmara
0.56
32°
BLACK
28°
0.370.43
0.80
0.39
0.40
0.39
0.70
0.47
0.49
0.69
0.80
0.70
0.17
-0.30
0.16
0.27
0.00
0.82
-0.08
44°
44°
40°
44°
winter index period of 1963-1969
anomalies for the negative NAO
(b) Composite winter precipitation
0.83
-0.13
-0.30-0.12
40°
40°
annual index period of 1963-1969
anomalies for the negative NAO
0.88
0.71
0.79
0.97
0.02
1.11
0.87
0.48
-0.03
0.10
1.29
-0.10
44°
(a) Composite annual precipitation
0.63
0.10
-0.22-0.32
0.49
0.64
0.38
0.85
0.68
-0.42
40°
36°
40°
36°
40°
36°
40°
d)
36°
40°
c)
0
0
-0.44
-0.66
-0.58 -0.33
-0.51
-0.25
-0.80
-0.83
28°
50 100 150 200 250
km
MEDITERRANEAN
-1.01
-1.26 -1.04
-1.35
SEA
-0.73
-1.10
-1.08
-1.10
-0.88
-0.64
-0.64
-0.61
-0.41
-0.81
-0.36
-0.52
36°
-0.26
-0.41 -0.65
-0.62
-0.10
-0.56
SEA
-0.39
-0.59
-0.81
-0.52
-0.59
-0.25
-0.13
-0.61
-0.21
36°
0.16
-0.18
0.72
-0.06
-0.69
-0.03
-0.25
-0.22
-0.33
-0.11
0.33
-0.26
-0.48
0.43
44°
44°
40°
44°
winter index period of 1989-1994
anomalies for the positive NAO
(d) Composite winter precipitation
-0.49
-0.26
-0.38
-0.17
-0.23-0.14
40°
40°
annual index period of 1989-1994
anomalies for the positive NAO
-0.72 -0.34
-0.46
-0.89
-0.64
-0.32
0.11
-0.21
-0.64
-0.29
0.24
-0.11
44°
(c) Composite annual precipitation
-0.48
-0.24
-0.44
-0.22
0.33 -0.25
40°
-0.49 -0.20
-0.42
-0.37
-0.22
SEA
-0.20
-0.35 -0.67
-0.94
36°
0.05
-0.37
-1.01
0.11
0.28
-0.17
0.04
-0.49 -0.29
-0.79
-0.40
-0.39
36°
0.26
-0.02
-0.57
-0.33
-0.21
-0.84
-0.46
-1.06
-0.67
32°
-1.05 -0.56
-0.65
-0.60
-0.86
-0.92
-1.07
-1.00
-0.92 -0.71
-0.98 -0.73
-1.16 -1.07
-1.29
Sea of
Marmara
-0.96
32°
-0.60
BLACK
32°
-0.49
-0.92
-0.65
-0.51
28°
km
SEA
-0.64
-0.98
-0.78
-0.10
-0.58
-1.30
-1.42
-1.08
28°
50 100 150 200 250
M E D I TE R R A N E A N
-1.18
-1.06 -0.71
-1.29
-0.99
-1.13
-1.18
-1.10
-0.57 -0.33
-0.90 -0.58
-1.01 -1.15
-1.15
-0.68
Sea of
Marmara
32°
BLACK
28°
-0.75-0.98
-0.61
36°
40°
36°
40°
Figure 8. As for Figure 3 (b) and (c), but for the negative (a) annual and (b) winter NAOI period of 1963–69, and for the positive (c) annual and (d) winter NAOI period of 1989–94
36°
40°
b)
36°
40°
SEA
AEGEAN
SEA
AEGEAN
SEA
AEGEAN
SEA
Copyright  2003 Royal Meteorological Society
AEGEAN
a)
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
1791
Int. J. Climatol. 23: 1771–1796 (2003)
0
0
1.43
1.07
1.04
0.72
3.56
1.85
28°
50 100 150 200 250
km
2.41
2.56
3.54
2.29
-0.54
0.67
1.17
2.65
36°
1.08
2.80 1.03
2.90
1.99
2.16
1.56
1.65
2.13
1.22
S E A
2.13
1.49
0.18
2.97 2.98
3.31
2.50
36°
1.01
0.43
0.55
1.97 1.41
1.02
36°
0.65
-0.48
2.12
SEA
1.85
0.52
-1.26
-0.77 1.38
2.06
0.85
1.22
3.85
36°
-0.52
0.67
0.80
-0.29
-0.17
1.03
0.32
2.98
1.78
32°
SEA
0.10
1.17
1.62
2.52
2.36
2.47 1.50
2.42 3.23
3.43
M E D I TE R R A NE A N
0.79 1.26
1.27
2.25
2.17
1.61 1.56
1.94
2.64
Sea of
Marmara
1.841.56
2.65
1.83
1.33
32°
2.74
0.02
BLACK
32°
3.00
1.49
0.62
1.60
28°
28°
50 100 150 200 250
km
0.73
1.21
SEA
-0.42
-0.13
0.25
1.44
1.29
0.95 2.01
1.17 0.95
2.19
0.95
MEDITERRANEAN
-0.98 1.75
-0.21
-0.35
-0.15
-0.68 0.57
0.70
0.61
Sea of
Marmara
32°
BLACK
28°
0.710.83
1.92
0.40
1.42
2.00
40°
-0.10 to 0.00
0.00 to 0.50
0.50 to 0.85
0.85 to 4.00
1.30
0.99
0.89
2.77
1.21 1.48
0.27
1.69
1.06
0.55 -0.09
40°
40°
-1.30
-0.85
-0.50
0.00
0.50
0.85
1.41
2.20
to -0.85
to -0.50
to 0.00
to 0.50
to 0.85
to 3.80
2.10
2.60
0.67 1.09
078. 1.65
2.31
0.93
-0.93
40°
1.26
3.74
0.75
-0.01
44°
(b) Winter precipitation
anomalies for the
negative NAO winter
index in 1963
0.01
2.14
0.63
0.65
0.68
0.38
0.67
44°
44°
(a) Annual precipitation
anomalies for the
negative NAO annual
index in 1963
2.56
2.65
1.98
1.90
2.32
1.86
2.33
44°
36°
40°
36°
40°
36°
40°
d)
36°
40°
c)
0
0
-0.66
-0.33
0.99 -1.04
1.51
-1.14
-1.46
M E D I TE R R A NE A N
28°
50 100 150 200 250
km
-0.79
32°
SEA
-1.29
-1.67
-2.02
36°
-1.97
SEA
-2.26
-2.27
SE A
36°
-2.55
-2.10
-2.21
-1.94 -2.17
-1.92
-2.15
-1.70
-2.52
-1.58
-1.39
-1.81 -1.18
-2.82
-2.19
-2.75
-2.26
-1.75
-1.13
36°
-1.28
36°
-1.67
-1.41
-2.19
-1.06 -1.37
-1.34
-0.65
-1.54
-1.84
-0.83
-0.17
-1.32 -1.16
-0.61
-1.85
-0.42
-1.42
-2.07
-1.86
-1.01
-1.73
-2.30
-1.99
-2.21
-1.09
-0.87
-1.17
-0.92
-1.08 -2.10
-1.58
-1.35 -1.88
-1.20
-0.08 -0.77
-1.24
-1.12
-0.74
-0.46 -1.62
-0.57 -1.22
-1.01
-2.52 -1.36
-2.32
0.08-0.15
-0.51
-0.84
Sea of
Marmara
32°
-1.34
BLACK
32°
SEA
-1.72
28°
28°
50 100 150 200 250
km
-0.67
-2.15
-1.66
-1.9-12.33
M E D I TE R R A NE A N
-1.42
-0.57 -1.41
-1.12
0.38
-1.07 -0.08
-0.14
-0.59 0.15
0.11
-1.57
-0.36 -0.88 -0.66
-0.36 0.29
-1.38
-1.27
Sea of
Marmara
32°
BLACK
28°
0.73
-0.30
-0.99
-1.06
-1.31
40°
-0.86
44°
-1.21
0.56
44°
(d) Winter precipitation
anomalies for the
positive NAO winter
index in 1973
-1.09
-1.03
-1.07
-0.81
-0.22
-0.15
-1.19
44°
44°
(c) Annual precipitation
anomalies for the
positive NAO annual
index in 1973
-1.17
-1.54
-0.29
-0.90
-0.84
0.01
-0.83
-0.54
-3.00 to -0.85
-0.85 to -0.50
-0.50 to 0.00
0.00 to 0.50
0.50 to 0.60
-0.81
-1.16
-1.00
-1.21
-0.83-0.99
40°
-2.34 -2.22
-2.04
-1.93
-1.16
40°
-2.20 to -0.85
-0.85 to -0.50
-0.50 to 0.00
0.00 to 0.50
0.50 to 0.85
0.85 to 1.60
-1.89
-1.78
-1.20
-0.89
0.43 -0.47
-1.12 -1.69
-0.04
-0.40
0.46
40°
36°
40°
36°
40°
Figure 9. Spatial distributions of the annual and winter normalized precipitation anomalies at 78 stations in Turkey, during the negative and positive NAO annual and winter indices
respectively: (a) and (b) 1963; (c) and (d) 1973
36°
40°
b)
36°
40°
a)
SEA
AEGEAN
SEA
AEGEAN
SEA
AEGEAN
SEA
Copyright  2003 Royal Meteorological Society
AEGEAN
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Int. J. Climatol. 23: 1771–1796 (2003)
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
1793
of 1973, 1974, 1983, 1984, 1989 and 1990, were closely linked to the extreme high-index NAO winters
in 1973 (+2.4), 1974 (+1.9), 1983 (+1.9), 1984 (+2.9), 1989 (+3.4) and 1990 (+1.9). One of the highest
positive NAOIs, with an anomaly value of 3.4 in the year of 1989, was also perfectly reflected in one of
the lowest cold-season cyclone activities for the lower latitudes of the Northern Hemisphere in 1988–89
(Serreze et al., 1997), and the lowest cyclone frequency for Turkey in the 1989 winter season (1988–89) and
annually (Türkeş, 1998a). On the other hand, coherent large-scale wet conditions in Turkey were detected to
have occurred during the extreme low-index NAO winters in 1963 (−4.0), 1968 (−1.1), 1969 (−4.3) and
1978 (−1.6). Results for some specific year examples are as follows. With respect to the annual and winter
precipitation, the most coherent widespread and most wet conditions in Turkey occurred during the negative
annual and winter NAOI in 1963 with anomalies of −2.16 and −4.0 respectively (Figure 9(a) and (b)). In
the 1963 winter season, very high and extremely above-normal precipitation conditions prevailed over most
of Turkey, except for the eastern and northeastern portions of the Anatolian Peninsula (Figure 9(b)). On the
other hand, during the normal annual and positive winter NAOI in 1973, with anomalies of +0.27 and +2.4
respectively, drier than normal conditions characterized the annual and winter precipitation at the majority of
the stations (Figure 9(c) and (d)). Very high and extremely below-normal conditions are evident particularly
in the winter precipitation at most stations in Turkey (Figure 9(d)).
4. DISCUSSION AND CONCLUSIONS
The following is a summary and discussion of the results and the main conclusions of the study:
1. The NAO, which is related to pressure alternation between the two large-scale dynamic centres of
action called the Azores high and the IL, is one of the best known atmospheric circulation patterns. The
NAO controls the weather and climate conditions and the extremes in the regions of the Atlantic and the
Mediterranean basin, including Turkey. Therefore, the present study investigated the relationships between
the variability of the precipitation in Turkey and the variability of the NAOI, and of the spatial and seasonal
precipitation changes associated with the extreme NAOI phases and the individual and persistent extreme
NAOI anomaly years.
2. The correlation analysis revealed that a negative relationship exists between the interannual variability
of most of the annual and seasonal precipitation series of Turkey, except in summer, and the variability of
the NAO indices, along with some inter-seasonal variations concerning the magnitudes of the precipitation
responses to year-to-year variability of the NAOI anomalies. Negative relationships that are particularly
strong in winter and less so in autumn become weaker in spring and almost non-existent in summer. Negative
correlation coefficients are significant at 61 stations in winter, 47 of which are at the 1% level, and at 27
stations annually, whereas they are significant at 23 and eight stations in autumn and spring respectively.
3. Composite analysis exhibited an apparent opposite anomaly pattern at most stations in Turkey, except in
summer, between the negative and positive NAOI phases. Annual, winter, spring, autumn and partly summer
composite precipitation means tended to increase during the negative NAOI phase, whereas the composite
precipitation means tended to decrease during the positive NAOI phase annually and in all seasons except
summer. In other words, precipitation in Turkey during the negative NAOI phase is mostly characterized
by wetter than long-term average conditions, whereas the positive NAOI responses mostly exhibit drier than
long-term average conditions throughout the year, except in summer.
The extreme NAOI responses, however, show some inter-regional differences at the same phase in terms
of the magnitude and sometimes the sign of the composite precipitation anomalies and means. Autumn and
particularly winter precipitation responses to the negative (positive) NAOI anomaly phase are characterized
by significant wet (dry) signals at most stations of the western and middle regions of Turkey. For instance,
according to Cramer’s test, wet and dry conditions in winter and autumn during the negative and positive NAOI
anomaly phases in the same seasons are significant at about 50% and the 28% of the stations respectively,
most of which are located in western and mid Turkey. On the other hand, extreme NAOI responses in the
continental eastern and southeastern regions and on the Black Sea coastal belt of Turkey are weaker than
those at, or opposite to, the other stations.
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
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M. TÜRKEŞ AND E. ERLAT
4. The winter correlation coefficients and precipitation anomalies stronger than other seasons in Turkey are
explained by the increased pressure differences between the large-scale centres of action in the North Atlantic
(the Azores high–IL pressure gradient) in this season. It can also be attributed to the fact that precipitation
occurrence conditions in Turkey in winter are controlled mainly by the Icelandic- and the Mediterraneanoriginated frontal depressions associated with humid air streams from the northeastern Atlantic (Türkeş, 1996a,
1998a; Türkeş et al., 2002). The correlation coefficients and precipitation anomalies in autumn, which are
relatively weaker than in winter, are very likely attributed to the well-known synoptic situation that the frontal
mid-latitude and the Mediterranean-type cyclones are not so active in autumn as in winter.
As for the much weaker and complex correlation and anomaly patterns in spring and summer, the
considerable contributions of local convective and orographic rains in addition to the frontal rains, and the
high interannual variability, particularly in summer, are considered as the main factors that cause weakening
of the associations between precipitation and the NAOI. The atmospheric control mechanism in summer
differs considerably from that of other seasons (Türkeş, 1998a; Kutiel et al., 2001; Türkeş et al., 2002):
summer dryness arising from the large-scale regional climate (i.e. the Mediterranean macro-climate), which is
controlled by both the mid-latitude and North African–Asiatic tropical (e.g. monsoon low) pressure systems,
influences most of the country in this season, except for the Black Sea coastal area and northeastern Anatolia.
Local and/or sub-regional physical geographic factors, such as topography, exposure and continentality, and
associated meteorological events (e.g. local convective showers/thunderstorms, orographic rains, etc.), also
diminish the real effects of the regional atmospheric control mechanisms over Turkey in summer.
5. The low-frequency fluctuations in the NAOI have been closely linked to the coherent large-scale
precipitation anomalies that have persisted, particularly in winter, over Turkey since the early 1960s. This
period included marked wet conditions in the 1960s and the late 1970s, and dry conditions in the early–mid
1970s, the late 1980s and early–mid 1990s and in the late 1990s. Annual and particularly winter precipitation
totals increased over most of Turkey during the negative NAOI period of 1963–69, except for 1967. Composite
winter precipitation means are significantly wet at 35 stations. On the other hand, annual and particularly
winter precipitation decreased at the majority of stations during the positive NAOI period of 1989–94.
Composite annual negative anomalies show a large spatial coherence over Turkey. Dry conditions, found to
be significant at 18 stations, are mostly distributed over the Marmara and Mediterranean rainfall regions and
the western and southern parts of the CCAN region. In winter, significant dry conditions are much more
evident for the positive NAOI period of 1989–94. Dry conditions are significant at 29 stations. Significant
dry signals show up over all rainfall regions, except for a large eastern region of the Anatolian Peninsula.
Marked wet conditions and meteorological drought events over Turkey in the individual years were also
found to be controlled by the extreme low and high index NAO anomaly years. The coherent large-scale
severe drought events in the winters of 1973, 1974, 1983, 1984, 1989 and 1990 were closely linked to the
positive anomaly phase conditions of the NAOI dominating in those years. For instance, during the normal
annual and strong winter NAOI anomalies in 1973, severe dry conditions were found in the annual and
winter precipitation at the majority of stations. On the other hand, coherent widespread strong wet conditions
occurring during the negative anomaly phase conditions of the NAOI prevailed in the winters of 1963, 1968,
1969 and 1978. For instance, during the negative annual and winter NAOI anomalies in 1963, the most
coherent widespread and strongest wet conditions occurred in Turkey.
6. Overall assessment. The year-to-year and longer time-scale variability of the NAOIs and the extreme
NAO phases were closely linked to the spatial and temporal variations and anomaly patterns in the precipitation
of Turkey. There is also a great resemblance between the spatial distribution and magnitude of the negative
correlation coefficients for the NAOIs and the precipitation series, spatial distribution patterns and severity of
the wet (dry) conditions with the negative (positive) NAOI phase and annually and in the winter and autumn
seasons. Coherent regions characterized with significant CCs coincide perfectly with the coherent regions
dominated by the extreme NAOI signals (i.e. significant wet or dry conditions). These clear associations have
increased our confidence with the results. Our results indicate that the NAO is one of the major atmospheric
sources of spatial and temporal variability of precipitation conditions in Turkey, as much as in the Atlantic,
Europe and the Mediterranean basin. Consequently, we suggest that the NAOI be used as one of the important
tools for detecting the main atmospheric causes of interannual and decadal spatial and temporal variations and
Copyright  2003 Royal Meteorological Society
Int. J. Climatol. 23: 1771–1796 (2003)
PRECIPITATION CHANGES AND VARIABILITY IN TURKEY AND NAO
1795
anomaly patterns in Turkish precipitation, as well as for contributing to future model studies for forecasting
regional changes and anomaly patterns for Turkey and its region.
ACKNOWLEDGEMENTS
We would like to thank the Climate Analysis Section (NCAR, Boulder, USA) and James W. Hurrell for
providing the NAOI data used in the study, and to express our special appreciation to Yurdanur Türkeş of
the TSMS for reviewing the first version of the manuscript. We would also like to thank the anonymous
referees for their constructive suggestions, and Dr Glenn R. McGregor, Editor of the International Journal of
Climatology, and Dr Ian D. Phillips, University of Birmingham, for improving the English of our paper.
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