INTERNATIONAL JOURNAL OF CLIMATOLOGY, VOL. 16, 1057-1076 (1996)

SPATIAL AND TEMPORAL ANALYSIS OF ANNUAL RAINFALL VARIATIONS IN TURKEY

MURAT TURKES State Meteorological Service, Department of Research, PO. Box 401, Ankam. Turkey

Received 15 September 199s Accepted 3 January 1996

ABSTRACT

This paper presents the spatial and temporal characteristics of Turkey’s annual rainfall data in the context of climatic variability. Basic data consists of the monthly rainfall totals from 9 1 stations with a record length ranging from 54 to 64 years, during the period 1930-1 993. Basic elements of the rainfall climatology have been examined and then normalized rainfall anomaly series have been analysed for long-term trend and fluctuation and changes in runs of dry and wet years, for all of Turkey, rainfall regime regions, and individual stations. All regional mean rainfall anomalies have tended to vary in a statistically coherent manner over the rainfall regions. Area-averaged annual rainfall series have decreased slightly over all of Turkey and apparently over the Black Sea and Mediterranean rainfall regions. Results of the Mann-Kendall test, however, have indicated that none of the decreasing trends in the area-averaged rainfall series were significant. Annual series of 17 stations showed a significant trend in the mean and a majority of these trends are downward. Many of the stations have experienced marked low-frequency fluctuations in the annual rainfall. The concurrences of the dry conditions between the rainfall regions and the rest of Turkey have appeared generally during the early 1930s, the late 1950s, the early 1970s, around the 1980s and the early 1990s and of wet conditions generally during the period 1935-1945, around the 1960s and the late 1970s. The change points for the beginning of h e r than normal conditions occurred in the early 1970s and early 1980s over most of the country. Annual rainfall variations over the rainfall regions except the Black Sea region were related closely to those of the rest of Turkey.

KEY WORDS: Turkey; rainfall regime regions; normalized rainfall; variance analysis; serial correlation and trend tests; Cramer’s test.

INTRODUCTION

With respect to the changes in rainfall amounts and distribution pattern, changes in surface albedo, cloud cover, general atmospheric circulation, atmospheric concentrations of greenhouse gases and of sulphate aerosols are important factors. Several analyses of long-term rainfall changes have been carried out by many researchers, globally and for specific regions. Folland et al. (1 992) and Srikanthan and Stewart (1 99 1) have concluded from well-known scientific papers and studies that most regional rainfall time-series have experienced fluctuations at different time-scales, rather than a notable or significant long-term trend. However, there is also some evidence for consistent decreasing trends in some regions of the world. Nicholson and Palao (1993) have pointed out that Sahel rainfall series for West Africa indicate a fairly persistent downward trend from 1950, including the strong dry period of 1968-1990. The general downward trends over most of Greece and Turkey, with abrupt decreases over the last 30 years and during the early 1970s and 1982-1993, respectively, were striking, when the rainfall variations in the eastern Mediterranean are considered (Repapis et al., 1989; Amanatidis et al., 1993; Tiirkev, 1995b). Furthermore, Jacobeit (1995) has assessed the impact of the atmospheric circulation changes due to increased greenhouse warming on seasonal rainfall at 9 1 Mediterranean stations by applying statistical down-scaling techniques, and has found common increases in the northern part and prevailing decreases towards the south. Estimated changes of Mediterranean rainfall in the future have shown some decreases in Greece and the western part of Turkey in the rainy period.

CCC 0899-84 1 8/96/09 1057-20 0 1996 by the Royal Meteorological Society

1058 M. TfjRKES

In Turkey, a limited number of studies have been carried out on rainfall variations and drought phenomena. Erdoian (1989) has analysed annual discharge data of six major river basins of Turkey, for the period between the water years of 1938 and 1988, and reported that major drought-dominated regimes occurred during the years of 1954-1955, 1960-1961 and 1972-1973. A severe and prolonged drought regime that had a countrywide impact was observed only during the period 1970-1 974. Using the annual and monthly rainfall data of 156 stations for the period 1956-1 987, Turkev (1 990) has found that severe dry conditions occurred over a considerable part of Turkey during the years 1956-1957, 1959, 1970, 1972-1973, 1977, 1982, and 1984. Widespread drought events occurred in 1970s. Major wet conditions dominated during the years of 1963, 1967-1969, 1976, and 1981. Tiirkev also showed that decreasing trends in the normalized annual rainfall anomalies were apparent in the Black Sea Region, while a low-frequency fluctuation about a slightly decreasing long-term mean existed in the coastal belt of the Mediterranean Region. Kadioilu (1 993) has shown that there has been a general decrease in winter rainfall and an increase in spring rainfall, using the monthly rainfall data of 18 stations for the period 1929-1990. ozgiirel and KoCman (1994) have analysed the rainfall data of the Aegean Region and show that annual and monthly rainfalls were well below normal in 1989 and in following years. They concluded that drought-affected areas extended from the Aegean coasts to the interiors during this period and suggested that cloud-seeding for the region could produce additional rain and prevent droughts in the short term. Toros et al. (1994) have examined seasonal and annual rainfall data of the western part of Anatolia, using 68 stations for the period 1930-1 992. They found a decrease in rainfall after 1982 and concluded that this decrease was not due to climatic change but that it was evidence only of a fluctuation in rainfall. Tiirke$ (1995a, b) has analysed the annual and seasonal rainfall data of 91 stations for the period 1930-1 993 and reported a decreasing trend over Turkey as a whole and particularly over the Black Sea and Mediterranean rainfall regions. Abrupt decreases and drought-dominated conditions in rainfall series occurred over much of the country during the early 1970s and during the period 1982-1 993. However, regional and countrywide changes in long-term annual rainfall totals and main characteristics of the rainfall climatology for the whole of Turkey have not been studied comprehensively as yet. The aim of this study is:

(i) to give essential information on Turkey’s rainfall climatology by examining descriptive statistical features of annual rainfall totals, major geographical factors influencing rainfall distribution, and characteristics of the spatial distribution of mean annual rainfall totals and of interannual variability of annual rainfall;

(ii) to show the nature and magnitude of the observed long-term trends and fluctuations by applying various statistical and graphical analysis methods to annual rainfall series for 91 stations, rainfall regions, and all of Turkey;

(iii) to quantify the spatial and temporal relationships of the regional rainfall variations by carrying out region to region and region to country concurrence and correlation analyses.

GEOGRAPHICAL CONTROL ON RAINFALL DISTRIBUTION

Main physiographic factors affecting Turkey’s climate are: (i) the Black Sea and Mediterranean basins; (ii) west to east oriented high mountain ranges along the northern and southern coasts of the Anatolia Peninsula; and (iii) the Anatolian plateau with a mean elevation of 1130 m. The seas surrounding Turkey from three sides act as natural passages for the frontal cyclones shifting from west to east. The eastern Black Sea and the area between the Gulf of Iskenderun and Cyprus are the secondary source andor deepening regions for a number of cyclones. The Atlantic Ocean and the Mediterranean Sea are the primary source regions for moist air masses causing the abundant rainfall over the windward slopes of the coastal mountain ranges and the interior mountains of the country. Troughs and frontal-type mid-latitude cyclones, associated with the prevailing upper level westerly flows, are considered as the principal climatic controls of rainfall. Orographic rise of the Atlantic originated maritime polar (mP) and Mediterranean (Med) air masses that support the frontal rise lead to heavy rainfall along the windward slopes of the Northern Anatolia Mountains and Taurus Mountains, respectively. The central and eastern parts of the Anatolia are somewhat protected from the effects of the moisture-bearing air masses, so precipitation is generally lighter than in other regions. These air masses lose their moisture content and get drier adiabatically, during their passage over the mountains and when descending along the leeward side of the mountains.

ANNUAL RAINFALL IN TURKEY 1059

The spatial distribution of annual precipitation over Turkey shows that mean annual rainfall totals decrease from coastal belts to the interior, with a steep gradient over the ranges of the Northern Anatolia and Taurus mountains (Figure 1). At most of the stations located on the Black Sea Coast, the amount of rainfall exceeds 1000 mm and reaches its maximum value on the eastern coast, for example 2304 mm in Rize. Along the major part of the Mediterranean coastal belt, mean annual rainfall is above 800 mm, but it increases up to 1500 mm and more on the high southern slopes of the Taurus Mountains. Deep valleys at the southern sides of the Northern Anatolia Mountains and plains with low plateaux at the northern sides of the Taurus Mountains are the major arid and semi- arid areas of Turkey owing to processes of the leeward slope subsidence. In the semi-arid Central Anatolia Region, mean annual rainfall ranges from 350 to 500 mm over a large area. Over the semi-arid South-eastern Anatolia Region, mean annual rainfall increases from south, where the rainfall amount is about 400 mm, to north, where annual rainfall is 800 mm, whereas it decreases towards margin of the Syrian Desert. The annual rainfall is more than 500 mm over a considerable part of the Eastern Anatolia Region, with the exception of low basins and deep valleys, and increases over highlands and mountains. Annual rainfall amounts in the Marmara and Aegean regions are less than in the Black Sea and Mediterranean regions, with the means ranging between 600 and 800 mm in the Aegean Region; west to east elongated deep valleys, however, allow the frontal cyclones to enter inland towards the east and to release abundant rainfall along those valleys.

As for the seasonality of rainfall, maritime polar weather types, which are carried by north-westerly upper air flows, cause heavy precipitation during the late autumn, winter, and early spring over the northern and western parts of Turkey, except in areas with rain-shadow. Frontal Mediterranean cyclones associated with the south- westerly air flows produce intensive rain showers and thunderstorms over western and southern parts of Turkey in late autumn and particularly in winter. In addition to the frontal rainfalls, convective and some frontal thunder- storms are important atmospheric processes responsible for rainfall over the continental interiors, particularly in spring and early summer. Topography and exposure produce microclimate effects superimposed on the mesoscale weather patterns in all seasons as well.

RAINFALL DATA

Monthly totals of the daily rainfall data recorded at 91 stations of the Turkish State Meteorological Service have been used. For both the station-based and regional analyses, the study covers the period 1930-1993. Average record length of the stations is 60 for the study period of 1930-1993, with a length of record varying from 54 years to 64 years. Many of these stations are located in the most heavily populated cities of Turkey and their populations have been growing rapidly. Moreover, many stations have faced local and regional air pollution problems owing to the rapid urbanization and industrialization in much of Turkey since the 1970s. Emissions from the coal-fired electricity plants have also reduced air quality in some districts of the country.

Records of the monthly rainfall totals have been examined in order to obtain homogeneous records and to ensure a good geographical representation where possible. First, a total of 130 stations has been selected for the analysis. A preliminary examination of the monthly data showed that a number of the monthly records had missing data. A number of year-month missing values, in which records having small gaps of not more than 5 per cent of the total number of monthly values, have been estimated by using the normal ratio method (Singh, 1992). In this estimating procedure, three nearby reference stations are chosen. These stations have to be in the same rainfall regime region as the base station having the missing record and surround it approximately. It was not possible, however, to estimate the missing data confidently for about 35 of the stations and these have been eliminated from the analysis. Then, statistical evaluation of homogeneity of the rainfall data was checked by using the non-parametric Kruskal- Wallis homogeneity test on the subperiods’ means (Sneyers, 1990). For calculation of the test statistics, observations of each subperiod are firstly replaced by their ranks rV as occupied in the total ordered sample. If k is the number of subperiods and ni is the sample size of the subperiods j , then the test statistic is written as

1060 M. TuRKES

a W

z W z rY rY w I-

W 5

a

a

- n

ANNUAL RAINFALL IN TURKEY 1061

where “J k

i= 1 j= 1 Rj = C rij and n = n,

The hypothesis of homogeneity of the series is rejected for the large values of X. Under the null hypothesis of homogeneity of the means, the statistic X is distributed approximately as x2 with (k - 1) degrees of freedom. In this study, sample size of the sub-periods has been taken as nj = 10 and the critical significance level of the test is at least a = 0.05. Homogeneity of the variances has also been verified by using the same test. In this case, ranks of the absolute values of the deviations from the long-term mean are used. Along with this test, a non-parametric test has been performed to supply a double-check of the results, particularly in cases of significant inhomogeneity. A subjective assessment for each statistically significant inhomogeneity has been made by means of additional information available from the plotted graphs and station history file. Finally, the climatological significance of each has been assessed and five more stations have been omitted from the analysis by this evaluation. When the station history files that include information for most of the remaining 91 stations were examined, it seemed that about 70 per cent of the stations had been moved to new locations during the study period. Most of these relocations vary between several metres and 5 km. It can also be reported that a systematic and countrywide raingauge change did not occur during the study period. However, some ordinary raingauge changes occurred at many individual stations at different times.

For the purpose of regional classification, the word ‘rainfall’ has been used to qualify precipitation in all regions, because most of the precipitation is in the form of rain at most stations, except those in the Eastern Anatolia Region. Using an index of seasonality (Glantz, 1987) and the percentage ratio of the seasonal rainfall totals to the annual amount (not presented here), Turkey has been divided into seven rainfall regime types for the regional analysis, primarily with respect to the seasonality of rainfall. Previous classifications and maps produced by various researchers (ErinC, 1969; KoCman, 1992) have also been taken into consideration. Basic characteristics of the rainfall regions and number of stations in each region used in calculating of area-averaged normalized series are given in Table I. The locations of the 91 stations over the rainfall regions are shown in Figure 2. Basic statistical characteristics and highest and lowest values of the annual rainfall totals, with the years of occurrence, are given in Table I1 for each station by rainfall regime region. The ratio of the mean deviation I MD I to the standard deviation CT

M E D I T E R R A N E A N RAINFALL REGIONS OF TURKEY

Figure 2. Rainfall regime regions of Turkey designated mainly in terms of the seasonality of rainfall and location of the stations used in the analysis.

1062 M. TURKE$

Table 1. Rainfall regime regions and number of the stations in each region

Number Rainfall region of station

Black Sea (BLS): uniform rainy with a maximum in autumn; temperate

Mediterranean (MED): markedly seasonal with a cool and heavy rainy winter and a hot dry summer; humid and semi-humid subtropical Continental Mediterranean (CMED): seasonal with a rainy winter and spring and a severe hot dry summer; semi- arid subtropical Mediterranean to Central Anatolia Transition (MEDT): moderate rainy winter and spring Continental Central Anatolia (CCAN): cool rainy spring and cold rainy winter and warm and light rainy summer; semi-arid steppe Continental Eastern Anatolia (CEAN): cool rainy spring and early summer with a very cold and snowy winter; semi-humid steppe and highland

8 1 1 24

14

4 20

10

Marmara (Mediterranean to Black Sea) Transition (MRT): uniform rainy with a warm and light rainy summer

is included as an indication of the normality of the distributions. For a normal distribution, this value is about 0.80 with 95 per cent probability limits of 0.75 and 0.85 for a record length of 50 values (Rodhe and Viji, 1976). A majority of the station data have positive skewness and the statistical distribution of most stations fits a log-normal distribution rather than a normal distribution, even though results of approximately 90 per cent of the stations lie within these confidence limits.

METHOD OF ANALYSIS

For the time-series analysis of the annual rainfall data, this study has adopted the normalization procedure proposed by Kraus (1977) and used later by several researchers, such as Shinoda (1990) and Srikanthan and Stewart (1991). The normalized annual rainfall anomaly (A,) for a given station is

where Rsy is the annual total rainfall for the station s during the yeary; RsRs and o, are the mean and standard deviation of the annual rainfall for that station, respectively. The area-averaged (regional mean) normalized annual rainfall anomaly (A,) for a given rainfall region is defined as

N.

s= 1

where N, is the number of regional stations operating in the yeary. Before using the A, series for the regional trend and fluctuation analyses, a variance analysis has been applied to assess whether these series are representative for the region as a whole (Kraus, 1977). The statistical importance of the ratio of variance estimates (variance in time/ variance in area) is determined by the F test in order to demonstrate that the geographical variations of the A, values between different stations within the given rainfall region are small, when compared with the temporal variations of the whole region represented by the A, values.

A nine-point Gaussian filter has been used as a low-pass filter in order to visually examine the shape of the trends and long-term fluctuations in the regional mean time-series. This filter has been applied to damp the fluctuations shorter than 10 years to aid understanding of the long-term evolution of the non-random characteristics of the series. In this method of filtering, the weighting of successive terms of a series varies symmetrically both backwards and forwards from a central weight (WMO, 1966). Sequential values of the statistics u ( f ) and #’(I) from the progressive analysis of the Mann-Kendall test (Sneyers, 1990) have also been plotted for the rainfall regions and all of Turkey. Without any trend, graphical representation of the values u(f ) and u’(t) indicates curves that overlap several times. In the presence of a trend, however, intersection of these curves enables the beginning of the trend or change in the series to be located, approximately.

In addition to the variance analysis described above, the following three statistical tests have been used. The first two tests are non-parametric tests and are applied to the normalized rainfall anomalies of the rainfall regions and

ANNUAL RAINFALL IN TURKEY 1063

Table 11. Basic statistical characteristics of the annual rainfall data for the 91 stations. ~ ~~~~

Year Year Standard Mean Length Mean Highest of Lowest of deviation deviation

I M D I lMDl Rainfall of rainfall rainfall occur- rainfall occur- (a) region Station record (mm) (mm) rence (mm) rence (mm) Skewness (mm)

BLS Rize Trabzon Giresun Samsun Sinop Zonguldak Bolu Adapazan

MRT izmit Goztepe vile Florya Corlu Liileburgaz Iorklareli Edime Tekirdag Bilecik Bursa

MED Canakkale Biga Bandirma Balikesir Edremit Dikili Akhisar Simav Salihli Manisa izmir Aydin Mugla Bodrum Fethiye Antalya Manavgat Alanya Silifke Mersin Uluki$a Adana Iskenderun Antakya

CMED Islahiye Kahramanmaraq Gaziantep

64 64 64 64 62 62 64 56 56 64 55 57 56 55 63 64 63 64 64 64 62 63 56 55 54 64 55 54 64 64 64 64 56 54 64 54 55 64 64 56 64 54 54 58 54 55

2304.2 808.3

1276.8 710.5 656.6

1207.5 536.3 807.0 78 1.4 677.9 790.6 639.6 560. I 591.6 565.6 584.9 566.6 436.7 694.9 612.1 742.7 703.0 579.1 713.6 627.0 585.9 825.6 485.8 730.5 682.0 647.2

1 183.2 729.9 89 1.6

1045.7 1 197.0 1064.4 607. I 592.5 337.4 642.3 749.2

1135.6 827.4 7 10.2 539.3

4045.3 121 1.6 1771.9 1012.2 990.4

1662.9 770.3

1097.6 1018.2 1047.7 1696.8 935.6 970.3 877.8 990.3

1127.4 958.5 624.7

1061.3 977.7

1175.0 1086.2

9 10.2 1165.3 979.5 902.4

1380.9

1931 1941 1933 1967 1967 1955 1933 1972 1940 1981 1981 1981 1940 1940 1966 1940 1940 1968 1942 1962 1962 1978 1940 1981 1955 1965 1940

750.1 1946 165.5 1965 116.5 1944 018.7 1940 903.4 1938 116.1 1944 379.4 1954

1914.3 2208.0 1770.4 1176.7 1039.0 5 16.8

1264.6 1322.4 1975.4 1266.7 1132.8 802.5

1969 1940 1981 1944 1968 1938 1968 1968 1976 1954 1954 1968

1600.0 573.3

1056.1 503.3 333.3 823.3 322.1 574.0 558.9 440.8 454.6 452.1 381.6 324.6 320.8 311.1 312.8 263.6 447.3 398.0 429.9 340.9 360.4 377.5 338.3 348.7 462.1 305.5 434.5 339.3 359.2 496.0 361.8 430.2 552.9 585.3 68 1.6 307.5 278.8 182.4 319.4 480.1 602.5 415.8 468. I 325.1

1966 1954 1945 1981 1986 1993 I930 1945 1956 I934 1957 1989 1945 1948 1932 1932 1932 1934 1934 1934 1934 1934 1957 1989 1992 1934 1989 1942 1992 1972 1992 1934 1992 1977 1973 1992 1990 1993 1973 1989 1972 1972 1989 1993 1973 1973

395.9 139.5 175.7 121.2 134.0 175.0 92.1

121.0 141.9 122.8 207.8 98.6

114.0 129.0 134.9 133.4 120.9 78.8

130.4 136.0 144.2 147.0 121.5 176.7 166.2 133.9 198.3 103.0 166.8 172.3 148.0 325.0 191.6 23 1.7 297.5 363.9 286.0 203.0 152.6 70.7

177.6 165.2 286.6 194.3 155.4 116.8

1,505 0.567 0.894 0.413 0.325 0.136 0.27 1 0.018 0.095 0.439 1.790 0.391 1.120 0.291 0.7 18 1.070 0.593 0.267 0.446 0.368 0.668 0.6 13 0,544 0.840 0.254 0.555 0.687 0.582 0.495 0.370 0.234 0.195 0.107

-0.087 0.333 0.737 0.7 16 0.805 0.487

-0.049 0.774 0.869 0.3 12 0.22 1 0.714 0. I79

285.2 114.2 142.5 99.4

104.8 132.7 71.6

100.3 122.5 100.4 154.9 81.0 86.0

103.6 107.5 100.6 95.1 61.9

103.1 111.0 111.4 108.8 96.8

134.9 131.6 103.1 152.4 80.2

129.3 141.2 117.4 261.5 159.8 190.0 239.2 270.8 229.6 164-9 1 16-6 55.3

135.0 128.3 234.5 158.4 124.8 94.4

0.72 0.82 0.81 0.82 0.78 0.76 0.78 0.83 0.86 0.82 0.75 0.82 0-76 0.80 0.80 0.75 0.79 0.79 0.79 0.82 0.77 0.74 0.80 0.76 0.79 0.77 0.77 0.78 0.78 0.82 0.79 0.80 0.83 0.82 0.80 0.74 0.80 0.81 0.76 0.78 0.76 0.78 0.82 0.82 0.80 0.81

(continued)

1064 M. TURKE$

Table 11. (continued).

Year Year Standard Mean Length Mean Highest of Lowest of deviation deviation

I M D I lMDl Rainfall of rainfall rainfall occur- rainfall occur- (a) region Station record (mm) (mm) rence (mm) rence (mm) Skewness (mm) -

U

Kilis Malatya Elazig

Adyaman Sanhurfa Siverek Diyarbakir Mardin Siirt Cine

Mu5

MEDT Kutahya usak

Isparta Burdur

CCAN Kastamonu Menifon Amasya Sebinkarahisar c o w Tokat Yozgat Sivas Eskiqehir Ankara Sivrihisar Afyon Polati Kirqehir Kayseri Ilgin Aksaray Nigde Konya KflCilllan

CEAN Ardahan Kars Sankamiq Igdir Agn Giimuqhane Bayburt Eaincan Hinis Van

62 64 63 59 55 56 64 64 55 64 55 64 64 54 64 63 64 57 64 64 61 55 64 64 64 64 64 64 64 56 64 55 58 64 64 55 64 63 54 55 62 64 56 55 61

52 1.5 386.1 427.0 841.8 761.3 47 1.8 55 1.6 488.9 709.9 73 1 .O 70 1.4 560.0 534.3 422.0 574.1 462.7 394.6 425.8 565.3 420.2 445.9 571.4 42 1.4 373.7 383.0 394.0 43 1.3 346.1 376.4 377.7 432.7 338.3 334.4 322.3 340.1 513.2 496.0 587.2 254.2 542.5 440.5 425.4 372.6 597.0 386.8

849.5 1935 596.5 1988 733.0 1976

1237.9 1963 2062.2 1954 790.9 1954 893.0 1976 748.8 1963

1191.1 1987 1229.1 1963 1165.4 1963 970.0 1940 731.4 1969 615.2 1969 968.9 1969 641.0 1931 654.1 1988 626.4 1988 829.0 1940 606.7 1983 742.3 1939 858.2 1983 596.9 1940 518.1 1963 617.6 1963 589.8 1968 679.1 1946 522.0 1963 541.9 1987 613.6 1988 608.7 1941 506.2 1987 470.8 1940

544.9 1968 513.4 1975 792.0 1967 744.1 1951 900.0 1967 501.2 1963 819.0 1940 726.9 1936 667.6 1963 633.1 1951 902.2 1942 541.5 1988

263.9 1932 174.1 1932 156.4 1932 479.2 1970 443.7 1970 219.3 1973 246.0 1932 206.2 1932 343.0 1990 427.1 1930 418.2 1990 324.2 1934 327.2 1934 269.2 1973 319.8 1989 307.7 1957 222.5 1950 266.8 1955 322.4 1952 280.5 1957 288.7 1957 391.0 1973 236.2 1932 193.2 1932 242.0 1977 215.4 1945 238.2 1974 197.2 1934 202.3 1932 261.9 1943 236.2 1974 161.0 1962 192.9 1970 143.7 1932 208.9 1934 315.8 1969 310.6 1961 393.2 1961 114.5 1970 323.0 1945 208.0 1952 255.3 1932 205.1 1955 270.6 1949 266.4 1950

136.8 93.2

107.9 176.4 27 1 .O 125.4 138.2 119.1 199.5 192.6 177.3 1 16.2 100.9 80.4

154.5 90.1 78.1 77.5

102.3 71.5 87.4 94.9 79.9 68.5 73.1 78.6 95.9 68.6 67.8 76.3 85.6 67.4 70.7 78.6 74.4

107.3 96.0

111.9 69.8

115.9 86.6 89.2 87.9

135.1 64.0

0.524 0.342 0.307 0.101 2.401 0.670 0.510 0.0 10 0.409 0.586 0.683 0.556

-0.137 0.198 0.3 17 0.181 0.893 0.548 0.204 0.289 0.842 0.641

-0.004 -0.425

0.539 -0.010

0.25 1 0.200

-0.056 0.809

-0.161 0.150

-0.290 0.373 0.291 0.466 0.540 0.478 0.700 0.360 0.546 0.563 0.605 0.132 0.267

105.4 74.5 81.5

140.3 186.9 93.1

106.9 94.4

156.6 156.5 141.5 89.9 85.1 61.4

124.3 75.8 60.6 62.3 82.7 57.3 66.6 73.9 63.8 51.0 53.6 59.5 15.9 53.0 53.8 57.6 67.6 51.2 55.8 61.0 60.7 85.7 73.4 88.7 52.0 92.8 64.9 68.2 68.9

106.5 53.1

0.77 0.80 0.76 0.80 0.69 0.74 0.77 0.79 0.78 0.81 0.80 0.77 0.84 0.76 0.80 0.84 0.78 0.80 0.8 1 0.80 0.76 0.78 0.80 0.74 0.73 0.76 0.79 0.77 0.79 0.76 0.79 0.76 0.79 0.78 0.82 0.80 0.76 0.79 0.74 0.80 0.75 0.76 0.78 0.79 0.83

ANNUAL RAINFALL M TURKEY 1065

individual stations. These randomness tests are distribution-free tests. The last test is a parametric one and used only for the mean annual rainfall totals of rainfall regions.

A possible alternative to randomness in a series of observations is some form of trend. However, trends in climatological series are rarely linear types. The WMO (1 966) and Sneyers (1 990, 1992) have recommended use of the Mann-Kendall or Spearman randomness tests against the trend in order to avoid the significant drawbacks arising from the use of statistical methods, such as the linear least-square regression approach to detect climate change. Therefore, the Mann-Kendall rank correlation test has been chosen to detect any possible increasing or decreasing trend in the series of observations (Sneyers, 1990). When the original observations are replaced by their corresponding ranks yi, for each term yi, the number ni of terms yj, preceding it (i > j ) is calculated with (yi > yj) and then the test statistic t is defined by

n

r = l t = C n ,

and its distribution function, under the null hypothesis, is asymptotically normal with mean and variance,

E(t) = n(n - 1)/4 and var t = [n(n - 1)(2n + 5)]/72

Using the two-sided test, the null hypothesis of absence of any trend is rejected for large values of lu(t)l with

u(t) = [t - E ( t ) ] / J v a r t

When the value of u(t) is significant at a desired level of significance, one can decide whether it is an increasing or decreasing trend depending on whether u(t) > 0 or u(t) < 0.

Sneyers (1 992) advised the use of the Wald-Wolfowitz serial correlation test combined with rank correlation trend tests, because changes in climatic series seem generally to proceed in an abrupt manner. Hence, the Wald- Wolfowitz serial correlation test has been used to determine randomness against the serial correlation (Sneyers, 1990). An alternative to randomness may indicate the presence of some form of fluctuation or of abrupt change. In most cases examining annual rainfall, a significant positive serial correlation signals the existence of a low- frequency fluctuation (Tiirkev, 1995a, b). Using the one-sided test of the normal distribution, the null hypothesis of randomness is rejected for large values of test statistic u(r).

Cramer’s test is performed to examine the long-lasting wet and dry conditions in a regional mean rainfall series by comparing the means of these subperiods with the mean of the whole period (WMO, 1966). The test statistic is shown by

2 112 tk = rk[n(N - 2)/(N - n - nrk)]

where

and N

i= I R = (1/N) c R;

R and c are the mean and standard deviation of the entire period of N years, respectively, and Rk is the mean of the subperiod of n years to be compared with R. The test statistic tk is distributed as Student’s t with (N - 2) degrees of freedom. The null hypothesis of no significant difference between the mean of a subperiod and the mean of a whole period is rejected with the two-tailed test for large values of I tk I. The minimum length of subperiod is taken as 3 years.

RESULTS

Spatial distribution of rainfall variability

interannual variability of annual rainfall totals over Turkey. The coefficient of variation is defined as Coefficients of variation for 96 stations have been computed in order to investigate the spatial pattern of the

cv = (as/Rs)lOO(per cent)

1066 M. TffRKE$

where j , is the long-term mean annual rainfall and a, is the standard deviation of annual rainfall totals for station s. The coefficients of variation decrease from the southern part of the country with a seasonal rainfall regime to the north where uniform or nearly uniform rainfall regimes dominate (Figure 3). The computed values of the coefficients of variation (not shown here) vary between 13.8 per cent on the eastern Black Sea Coast (in Giresun) and 35.6 per cent over the South-eastern Anatolia Region (in Adiyaman). The arid and semi-arid Continental Mediterranean rainfall region and humid Mediterranean Coast exhibit high rainfall variability. The coefficients of variation are well above 25 per cent on the coastal zone of the Mediterranean rainfall region and almost all of the Continental Mediterranean rainfall region. Coefficients of variation of less than 25 per cent have the largest geographical extent by covering approximately four-fifths of lkrkey. Areas with coefficients over 20 per cent are likely to have more frequent and severe droughts because of the low reliability of the normal rainfall (Turkev, 1990). Low values of coefficients observed over the uniform rainy Black Sea rainfall region imply high rainfall reliability.

Variations in countrywide and regional mean series

Before using the regional mean normalized series for trend and fluctuation analysis, the variance analysis has been applied to the regional data in order to assess whether a regional series adequately represents the region as a whole. Using the ratios of the variance estimates in time to the variance estimates in the area, it is apparent that all area-averaged rainfall anomalies tend to vary in a statistically coherent manner over the rainfall regions (Table 111). It is also observed that rainfall variations represented by the individual stations within each rainfall region are highly correlated. The resultant ratios of the variance estimates exceed the 1 per cent critical limiting values of the F distribution. The resultant test statistics of the statistical methods applied to the regional mean normalized rainfall anomalies are presented in Table IX The Mann-Kendall rank correlation test produces negative test statistics for almost all regional mean normalized series. None of these decreasing trends is significant at the 5 per cent level. When the 10 per cent level is taken into consideration for the test of significance, it can be accepted that normalized rainfall anomalies of the Black Sea and Mediterranean regions indicate a significant downward trend in the mean.

The time-series plots for all of Turkey (Turkey's 91-station series) indicate a slightly downward trend in annual rainfall, with a low-frequency fluctuation (Figure 4 (la and Ib)). Considering the line smoothed by the nine-point Gaussian filter, normalized rainfall anomalies for Turkey are characterized by four major wet periods, during the years of 1935-1944, 1951-1954, 1962-1969, and 1975-1981, and three major dry periods, during the years of

Figure 3. Geographical distribution of the coefficients of variation for annual rainfall totals in firkey.

ANNUAL RANFALL IN TURKEY 1067

Table 111. Results of the variance analysis for the area-averaged normalized rainfall series

Rainfall region N

Variance estimation

V(time) V(area)

F ratio

V(time)/ V(area)

BLS MRT MED CMED MEDT CCAN CEAN

500 66 1

1422 828 246

1237 589

3.17 5 .3 1

11.45 8.60 2.91 7.71 4.89

0.69 0.55 0.52 0.37 0.35 0.64 0.54

4.6 1 * 9.72*

22.18* 22.96*

8.41* 12.03* 9.13*

* Significant at the 1 per cent level

Table IV Results of the statistical test for the area-averaged normalized rainfall series

Test

Rainfall region

Wald-Wolfowitz Mann-Kendall 44 4)

BLS MRT MED CMED MEDT CCAN CEAN TURKEY

- 1 . 1 -0.1

1.2 -0.4

1.1 -0.5 -0.6

0.2

- 1.74 -0.93 - 1.80 -0.13 - 1.22

0.5 1 -0.80 - 1.29

1955-1961, 1970-1974, and 1982-1993 with the exception of the 2-year wet break of 1987-1988. After the marked wet spell of the 1962-1969 period, dry conditions became dominant and reached a countrywide peak of severity in 1989. When the means of subperiods are compared with the long-term mean, wet conditions during the years of 1935-1 944 and 1962-1 969 and dry conditions during the years 1970-1 974 are significant at the 5 per cent level. The driest year of the countrywide series is 1932, with a negative anomaly of - 1 e40, whereas the wettest one is 1940 with a positive anomaly of + 1.30. Area-averaged normalized rainfall anomalies for rainfall regime regions, however, exhibit some similarities and differences to those of countrywide anomalies, in terms of the severity, timing of occurrence, and length of dry and wet anomalies, which are detailed below.

The time-series plots of the Black Sea Region show a slightly decreasing trend in annual rainfall, with a high interannual variability (Figure 4 (2a and 2b)). This decline in the annual rainfall has been intensifying, particularly since the beginning of the 1970s. Almost all years within the period of 1972-1986 are characterized by negative rainfall anomalies. After the wet period 1987-1992, dry conditions reached a regional peak of severity in 1993. This negative anomaly in 1993 is also the largest one when compared with other rainfall regions. The wettest year of the regional mean rainfall series occurred in 1933. Comparison of the subperiods with the overall mean indicates that wet and dry conditions during the periods of 1930-1941 and 1972-1986, respectively, are significant at the 1 per cent level.

The time-series plots of the Marmara Transition Region depict a weak fluctuation about a stable long-term mean (Figure 4 (3a and 3b)). Regional mean normalized anomalies experience four wet conditions, during the periods of 1935-1944, with the regional wet peak in 1940, 1951-1955, 1962-1971, and 1978-1981, with a wetter year of 1981; along with the five dry periods of 1930-1934, 1945-1950, 19561961, 1972-1977, and 1982-1993. Wet conditions during the periods of 1935-1 944 and 1962-1 97 1 are significant at the 5 per cent level, whereas dry and wet conditions during the periods 1930-1934 and 1978-1981, respectively, are significant at the 1 per cent level. The dnest year of the regional mean series is 1934, with a large negative anomaly of -1.90, whereas the wettest

1068 M. T o m $

1 ](a) Turkey I @I Turkey

3

.............................................................

1.'" Black Sea 2 ..............................................................

2 ha) Black Sea 1

Marmara Transition 2 ..............................................................

3 1 (a) Marmara Transition I 1: g1

3 0 8 -1

l o 6 -l

-2 z -2

Mediterranean 2 ..............................................................

4 3 1 (a) Mediterranean

91 3 0 e a -1

-2

.t z -2

Year Figure 4. Variations and trends in annual rainfall series over Turkey and the rainfall regions. (a) Normalized annual rainfall anomalies with nine-

point Gaussian filter (-); @) sequential values of the statistics u(i) (-) and u'() (-.-) from the Mann-Kendall test, with the critical significance value for the 5 per cent level (..... ).

ANNUAL RAINFALL M TURKEY

5 ](a) Continental Meditarranean

1069

6 1bJ Maditerranean Transition

7 ](a) Continental Central Anatolia

2 2

8 3

)(a1 Continental Eastern Anatolia

- 3 9 7

)(b) Continental Mediterranean I ................................... 2 - s 3 1

s o 3 -1

U - r. ................. i ............................................

Mediterranean Transition ............................................

1 (b) Continental Central Anatolia I ....................................

.............................................................. -3 9 9

3 (b) Continental Eastern Anatolia ..............................................................

-3 9*

Year

Figure 4. (continued).

1070 M. TfSRKE$

Table V Correlation coefficients of the normalized rainfall anomaly series between the rainfall regions and between a rainfall region and the rest of Turkey (excluding that region).

Rest of BLS MRT MED CMED MEDT CCAN CEAN Turkey

BLS MRT MED CMED MEDT CCAN CEAN

0.3 1 * -0.01 0.07 0.12 0.41 ** 0.5 1 ** 0.28* 0.69** 0.28* 0.69** 0.55** 0.33** 0.67**

0.50** 0.77** 0.50** 0.28* 0.61** 0.43 * * 0.61** 0.56** 0.59**

0.63** 0.39** 0.76** 0.68** 0.75**

0.61 **

* Significant at the 5 per cent level. ** Significant at the 1 per cent level.

year is 1940, with a large positive anomaly of + 2-30. Some large cities located in this region, such as Zstanbul, have had significant difficulties in supplying enough freshwater for daily use since the mid-l980s, and particularly since 1989.

The time-series plots of the Mediterranean Region show a low-frequency fluctuation about an apparently decreasing long-term mean (Figure 4 (4a and 4b)). The smoothed rainfall anomalies of the Mediterranean Region are characterized by four main wet spells, during the periods of 1935-1947, 1951-1955, 1960-1969, and 1975- 1981; and five dry conditions, during the periods of 1932-1934, 1948-1950, 19561959, 1970-1974, and 1982- 1993. Dry conditions during the periods of 1932-1934 and 1982-1993 exhibit strong significance at the 1 per cent level; wet conditions over the periods of 1935-1947 and 1960-1969 are significant at the 5 per cent level. The years of 1940 and 1981 are the wettest two years, with an equal positive anomaly of + 1.70, whereas the years of 1932, 1934, and 1989 are the dnest three years, with an equal negative anomaly of -1.30.

The time-series plots of the Continental Mediterranean Region exhibit high-frequency fluctuation about an unchanged long-term mean (Figure 4 (5a and 5b)). In spite of this high year-to-year variability, the existence of dry conditions and some wet conditions that are characterized by shorter spells of wet years than of dry years can be documented. Major dry spells are observed during the periods of 1930-1934,1955-1962,1970-1975,1982-1986, and 1989-1990. After the period 1935-1949, wet conditions occur during the wet periods of 1950-1954, 1963- 1969, and 1987-1988. Dry and wet conditions during the periods of 1930-1934 and 1963-1969 are significant at the 1 per cent level and the wet condition of 1950-1954 is significant at the 5 per cent level. Dry conditions have become dominant since 1970, as in the majority of the other rainfall regions. The years of 1954 and 1976 are the wettest two years of the regional mean record, with an equal positive anomaly of + 1.70, whereas 1932 is the dnest year, with a negative anomaly of -2.0.

Normalized rainfall anomalies of the Mediterranean Transition Region tend to show an apparent low-frequency fluctuation about a slightly decreasing long-term mean (Figure 4 (6a and 6b)). Regional mean rainfall anomalies experience four major wet conditions, during the periods of 1936-1946, 1951-1955,1959-1969, and 1978-1981; along with the five dry conditions, during the periods of 1930-1935, with the regionally driest peak of -1.80 in 1932, 1947-1950, 19561958, 1970-1977, and 1982-1993. The wet conditions during the periods of 1936-1946 and 1959-1969 are significant at the 1 and 5 per cent level, respectively. The long-lasting dry spell in the period 1982-1993 indicates strong significance at the 1 per cent level. The year 1940 is the wettest one of the regional record, with a positive anomaly of + 2.0. Regional mean rainfall tends to decrease and increase at almost the same amount in dry and wet years, during most of the overall period. This situation has changed from 1982 towards a spell of dry years.

The time-series plots of the Continental Central Anatolia Region depict a high-frequency variability rather than a low-frequency fluctuation (Figure 4 (7a and 7b)). This is the only regional mean rainfall series that tends to increase more in wet years than it decreases in dry years, and to have a greater frequency of wet years than dry years, during the period 1970-1993. Certain dry and wet spells were pronounced, even though regional rainfall

ANNUAL RAINFALL IN TURKEY 1071

anomalies exhibit a high year-to-year variability over the region. Wet conditions dominate during the periods of 1936-1942, 1963-1969, and 1975-1988, with the highest wet anomaly in 1988, whereas dry conditions occur during the periods of 1930-1935, 1949-1962, and 197&1974. Wet conditions during the periods of 1936-1942 and 1975-1988 are significant at the 5 per cent level. The year of 1932 is the driest year of the regional mean series, with a high negative anomaly of - 1.80.

The normalized rainfall anomalies of the Continental Eastern Anatolia Region show a high-frequency variation about a slightly decreasing long-term mean (Figure 4 (8a and 8b)). In spite of a spell of wet years during the period 1930-1942 and some marked wet anomalies occurring in the rest of the series, dry anomalies dominate generally over the regional series, with respect to the relative frequency of the dry and wet years and the length of dry and wet spells. Regional mean normalized series experience three wet conditions, during the periods of 1930-1942, 1963-1969, and 1986-1988; along with two long dry conditions, during the periods of 1943-1962 and 1970- 1985. Wet conditions during the periods of 1930-1942 and 1986-1988 and dry conditions of 1943-1962 are significant at the 5 per cent level. The driest year of the regional mean series is 1932, with a negative anomaly of - 1.40, whereas the wettest one is 1963, with a significant positive anomaly of + 2.10.

Interregional comparison of rainfall variations

and the rest of Turkey for a year y is expressed as Following the procedure by Shinoda (1 990), the concurrence of a dry or wet condition between a rainfall region

C, =A,, , x AT,

where A,,, and AT, are the area-averaged normalized anomalies for the region and the rest of Turkey (excluding that region), respectively. The concurrence of the dry and wet conditions between a rainfall region and the rest of Turkey is shown in Figure 5 for all regional mean series. A concurrence of dry and wet conditions is apparent between the area-averaged annual series of the rainfall regions, except in the BLS rainfall region, and the series for the rest of Turkey. With the exception of the BLS rainfall region, most of the computed values are positive during the 64-year study period. Similar results are also found approximately between all pairs of the rainfall regions (not shown here). Successive larger values are observed particularly between the MRT, MEDT, CCAN and CEAN rainfall regions and the rest of Turkey. The concurrence of dry conditions between the annual series of the rainfall regions and series of the rest of Turkey (excluding these regions) appears generally during the early 1930s, the late 195Os, the early 1970s, around the 1980s and the early 199Os, whereas the concurrence of the wet conditions is observed generally during the period 1935-1945, around the 1960s and the late 1970s.

The interregional spatial coherence of the annual rainfall over Turkey is objectively quantified by using the region-to-region correlation coefficients. Correlation coefficients of the normalized rainfall series between all pairs of rainfall regions and between a rainfall region and the rest of Turkey (excluding that region) are given in Table V Most of the regional mean rainfall anomaly series except the series of BLS are positively correlated with other series at the 1 per cent significance level. Weak correlations are observed between the northern and southern areas of Turkey, as expected. The BLS rainfall region shows a weak relationship with the other regions and the rest of Turkey, whereas the MEDT and CCAN rainfall regions correlated most highly with other rainfall regions and the rest of Turkey. Normalized rainfall series of the MEDT and CCAN rainfall regions, with the highest correlation coefficients as a result of being surrounded by other rainfall regions, are more representative for the rainfall variability over Turkey. Significant positive correlations between the series of the rainfall regions and the series of the rest of Turkey (excluding these regions) also show that annual rainfall variations over most of the rainfall regions are related closely to those of the country during the study period.

Variations in station-based rainfall series

The test statistics obtained with the Mant-Kendall rank correlation and Wald-Wolfowitz serial correlation tests for the normalized annual rainfall anomalies of 91 stations and geographical co-ordinates of these stations are given in Table VI. Results may be summarized as follows.

1072 M. TURKES

MRT X (TURKEY-MRT) BLS x OURKEY-BLS) 2

1.5

1

0.5

0

5.5

-1 1

MED X (TURKEY-MED) CMED x (TURKEYCMED) 3- 3 -

2.5 . 2.5 *

2 . 2 - 1.5 - 1.5.

1 .

-\930 1940 1950 1960 1970 1980 1990

2.5 . 2.5 . 2 - 2 .

1.5. 1.5. 1 - 1 -

0.5 . 0.5 . 0 . 0 .

-0.5 * 5.5 - -1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1 4 9 4

CE4N x CTURKEYCEAN)

0.5 0

5.5 '-!!

Figure 5. Concurrences of dry and wet conditions between the annual rainfall anomaly series of the rainfall regions and the series for the rest of Turkey.

ANNUAL RAINFALL IN TURKEY 1073

Table VI. Results of the Mann-Kendall (M-K) and Wald-Wolfowitz (W-W) tests.

Latitude (N) Latitude (N) and M-K W-W and M-K W-W

Region Station Longitude (E) u(t) u(r) Region Station Longitude (E) u(t) u(r)

BLS Rize Trabzon Giresun Samsun Sinop Zonguldak Bolu Adapazan

MRT i m i t Goztepe Sile Florya Corlu Liileburgaz Kirklareli Edirne Tekirdag Bilecik Bursa

MED Canakkale Biga Bandirma Balikesir Edremit Dikili Akhisar Simav Salihli Manisa izmir Aydin Mugla Bodrum Fethiye Antalya Manavgat Alanya Siliflce Mersin UlukiSla Adana Iskenderun Antakya

4 1 "02'40"3 I' 4 1 "00'-39"43' 40"55'-38"23' 4 1 O 17'-36O 18' 42"Ol'-35" 10' 41 "27'-3 1'48' 40"44'-3 1 "3 6' 40"47'-30"25' 40"46'-29"56' 40"58'-29"05' 41'1 1'-29'37' 40"59'-28"48' 41" 10'-27"47' 41 "24'-27"2 I ' 41"44-27"14' 4 1 40'-26" 3 4' 40" 59'-27" 33'

40" 1 1'-29'06' 40"09'-29" 5 8'

40"08'-26"24' 40" 13'-27" 15' 40'2 1 '-27"58' 3 9" 39'-27" 52' 39"35'-27'01' 39"03'-26"52' 38"55'-27"5 1' 39"05'-28" 59' 38"29'-28"08' 38"37'-27"27'

3 7" 5 l'-27" 50' 38"26'-27" 10'

37" 13'-28"22' 37"02'-27"26' 3 6" 3 7'-29" 07' 36"42'-30"44' 36"47'-3 1'26' 36"33'-32"OO' 36"23'-33"56'

37"33'-34"29' 36'48'-34"38'

36"59'-35"2 I' 36"35'-36" 10' 36'12'-36"10'

-2.47* -1.19 -0.95 - 1.54 -0.79 -0.65 +0.96 -0.28 -0.06 +0.36 +1.01 -0.59 -0.68 -0.64 -0.94 - 1.80 -1.07 +o. 18 -2.06* -1.19 -1.12 +0.46 -2.26* - 1.60 -2.82** - 1.86 - 1 .oo +0.07 -0.59 - 1.50 -2.1 1 * -0.83 -2.67** -3.21** -0.66 -3.63** +0.60 -0.94 - 1.28 -3.00** +0.23 - 1.46 -1.10

+0.62 CMED Kilis -0.50 Malatya -0.27 Elazig

-0.28 Adiyaman -1.20 $anliurfa +0.29 Siverek +0.63 Diyarbakir +1.19 Mardin +0.02 Siirt + I .62 Cine -0.37 MEDT Kiitahya

+2.39** Burdur

+0.54 CCAN Kastamonu +0.36 Menifon -0.92 Amasya +0.73 Sebinkarahisar +0.75 c o r n -0.30 Tokat +1.06 Yozgat +1.13 Sivas +1.23 Eskiqehir +o. 18 Ankara +1.28 Sivrihisar +2.09* Afyon +0.18 Polatli +1.56 Kiqehir +0.56 Kayseri

+1.83* Aksaray +1.31 Nigde +1.87* Konya +0.34 Karaman +2.13* CEAN Ardahan +0.40 Kars +1.69* SankamiS +0.08 Igdir

-0.07 Giimushane +0.76 Bayburt +1.56 Erzincan

+0.19 Mu9

+0.24 usak

-0.32 Isparta

+0.69 Ilgln

+1.21 A&

36"43'-37"07' 3 8" 2 1'-3 8" 1 9' 38"41'-39" 14' 3 8.44'4 1 3 1 ' 37"45'-38" 17' 37"08'-38"46' 37"46'-39" 19' 37'53'40" 12' 37" 18'40'44' 3 7055'4 1 "57' 37" 19'42'1 1' 39'25'-29" 58' 38"41'-29"24' 37"40'-30"20' 3 7'45'-30" 3 3' 4 1 "22'-33"47' 40"52'-35"28' 40"39'-35"51'

40"33'-34"57' 40" 18'-38"25'

40" 18'-36'34' 39"49'-34"48' 39"45'-37"01' 39"46'-30"3 I' 39"57'-32"53' 39" 27'-3 1 O 32'

3 9" 3 5'-3 2" 09' 3 8" 45'-30" 32'

39"08'-34" 10' 3 8"45'-35"29' 38' 17'-3 1'55' 38"23'-34"03' 37" 58'-34"4 1' 37" 58'-32"33' 37" 11'-33" 13' 41"07'42"43' 40" 37'43'06' 40"20'42" 34' 39'55'44'03' 3 9" 44'43 O 03'

40" 1 5'40" 14' 39"45'-39"30'

40" 28'-39"28'

-1.58 +0.42 +1.6 -1.05

-1.15 -0.45 -3.33** +1.62 -1.70 +1.30 -0.78 -0.66 -0.10 -0.35 +0.78 -0.36 -0.28 -0.29 -0.09 +1.50 +0.86 +1.02 +0.12 +2.05* -0.81 -0.44 -1.68 +0.68 -2.67** +1.69 +1.68 +1.01 +2.21* +2.05* +1.70 +1.55 +0.74 -0.58 +2.22* -0.47 -0.92 +1.31 +040 +1.10 +1.54 +0.81 -0.40 -1.16 +1.85 -0.09 +0.36 +0.68 -2.31* +1.12 -0.01 -1.51 +0.61 +1.20 +1.62 -0.64 -2.64** +2.35** +0.08 -0.28 -2.22* + I .76* -0.21 +2.18* -0.48 +2.83** -0.01 -0.20 -3.19** -0.43 +1.45 +1.80* +0.31 -0.82 +0.54 +0.06 +0.89 -0.47 -1.26 +0.84 -0.29 -0.01

(continued)

1074 M. TURKE$

Table VI. (continued).

Latitude (N) Latitude (N) and M-K W-W and M-K W-W

Region Station Longitude (E) u(t) u(r) Region Station Longitude (E) u(t) u(r)

CMED Islahiye 37"02'-36'38' -1.60 + 0.93 CEAN Hinis 39'22'41'42' -0.18 + 1.88* KahramanmaraS 37"36'-36'56' -0.57 + 0.94 Van 38"27'43" 19' + 0.27 -0.64 Gaziantep 37"05'-37'22' -0.36 + 0.30

* Significant at the 1 per cent level. ** Significant at the 5 per cent level.

(i) in the BLS rainfall region, one station indicates a statistically significant decreasing trend in the mean. (ii) in the MRT rainfall region, one station indicates a significant decreasing trend in the mean.

(iii) in the MED rainfall region, seven stations indicate a significant decreasing trend in the mean. Five stations

(iv) in the CMED rainfall region, only one station indicates a significant decreasing trend in the mean, even though

(v) in the MEDT rainfall region, one station indicates a significant decreasing trend in the mean. (vi) in the CCAN rainfall region, five stations indicate a significant trend and two of them with increasing trend.

This is the only rainfall region where many of the annual rainfall series tend to increase rather than to decrease, although most of the observed trends are not significant. Five of the stations have a significant positive serial correlation coefficient.

(vii) in the CEAN rainfall region, one station indicates a significant decreasing trend. Two stations have a significant positive serial correlation coefficient.

When the results for the total of 91 stations are assessed together, it is concluded that normalized annual rainfall series of 17 stations show a significant trend in the mean and that 15 of them are decreasing trends. Significant decreasing trends are major characteristics of the Mediterranean Region. Fifteen stations depict a significant positive serial correlation coefficient. Time-series plots of the normalized rainfall anomalies of these stations show low-frequency fluctuations, mostly about a decreasing long-term mean (not shown here).

depict a significant positive serial correlation coefficient.

10 of the total 14 stations show a tendency to decrease.

SUMMARY AND CONCLUSIONS

Summer dryness, which is recognized as a normal climate characteristic of the Mediterranean macroclimate region, and long-lasting dry episodes that can occur in every season associated with the high interannual variability in rainfall have been creating great pressure on the water resources of Turkey. Various human activities and particularly misuse of water owing to urbanization and agricultural practices make this pressure more severe. In this paper, annual normalized rainfall series have been analysed to prove the long-term variations in time and space by using mainly non-parametric statistical methods. The non-parametric randomness tests used in this study have been recommended by WMO (1966, 1988), Sneyers (1990, 1992), and many researchers, as being the most powerful basic tests for detecting the changes of climatic variables. The main concern is to investigate the nature and extent of the non-randomness in the normalized rainfall series. The form of non-randomness for this study consists of some types of persistence (serial correlation), trend and fluctuations, but not periodicity.

The basic data consist of the monthly rainfall totals of 91 stations for the period 1930-1993. The homogeneity of rainfall data has been checked using the Kruskal-Wallis test for homogeneity of the means and variances. According to the results of the objective and subjective analyses, annual rainfall series of 91 stations and area- averaged series of the rainfall regions appear to be homogeneous. It has also been found that all area-averaged rainfall anomalies tend to vary in a statistically coherent manner over the rainfall regions. Results of the Mann- Kendall test have pointed to decreasing trends in the area-averaged normalized rainfall series of the Black Sea and Mediterranean rainfall regions and all of Turkey. None of the test statistics for these regions, however, is significant at the 5 per cent level. Statistically significant decreasing trends have been found in the annual rainfalls at 15

ANNUAL RAINFALL IN TURKEY 1075

stations, of which 7 are in the Mediterranean rainfall region. Many of these significant downward trends appear to have occurred as a result of abrupt decreases during the last 2&25 years of the study period. Only two stations in the Continental Central Anatolia Region have shown a significant increasing trend in the mean. Fifteen of the station-based annual series have a significant positive serial correlation. This result supports the observed low- frequency fluctuations in the time series plots of these stations. Graphical plots of the regional mean rainfall anomalies exhibit low-frequency fluctuations over the Mediterranean and Mediterranean Transition regions and some high-frequency variation over the continental type rainfall regions. For all of Turkey’s rainfall anomaly series, dry conditions are found during the period 1955-1961, during the early 1970s and from the early 1980s to 1993, whereas wet conditions occur during the periods of 1935-1944 and 195 1-1954, around the 1960s and during the period 1975-1 98 1. Abrupt decreases and drought-dominated conditions in annual rainfall occurred over most of Turkey in the early 1970s and recently during the period 1982-1993. These dry conditions could be associated generally with the persistence of drought-favouring anticyclonic weather types over the Central and Eastern Mediterranean Basin (Tiirkev, 1990).

With the exception of the BLS rainfall region, a concurrence of dry and wet conditions is found between the area-averaged series of all rainfall regions and the series for the rest of Turkey, during the 64-year study period. Successive and larger positive values are observed particularly between the MRT, MEDT, CCAN, and CEAN rainfall regions and the rest of Turkey. A concurrence of the dry conditions between the series of the rainfall regions and the series for the rest of Turkey appears generally during the early 1930s, the late 1950s, the early 197Os, around the 198Os, and the early 199Os, whereas wet conditions are observed generally during the period 1935-1 945, around the 1960s, and the late 1970s. Correlation coefficients between the annual rainfall series of the rainfall regions are strongest for the regions that are close to each other, as expected. There is a weak relationship between the CEAN rainfall region and the western regions and almost no relationship between the BLS rainfall region and the Mediterranean type rainfall regions. Significant positive correlations and large positive concurrence values between the series of the rainfall regions and the series for the rest of Turkey show that rainfall variations over most of the rainfall regions are closely linked with those of the rest of the country.

The application of the Mann-Kendall test combined with the Wald-Wolfowitz and Cramer’s tests to normalized rainfall series showed that annual rainfall variations in Turkey seem generally to have proceeded in an abrupt manner and a long-term fluctuation about an unchanged or a slightly decreasing long-term mean, elsewhere with a strengthening downward trend. However, in addition to the likely effects stemming from the relative weaknesses of the statistical procedures used in the study, some segments of the trends and abrupt changes, particularly in the individual station series, may have been affected by urbanization and relocation of the stations.

ACKNOWLEDGEMENTS

The author would like to express his thanks to his colleague Utku M. Siimer of the Turkish State Meteorological Service (TSMS), who prepared a specific programme for variance analysis and helped to mange the rainfall data set. The author is also very grateful to Yurdanur Turkev of the TSMS and H. Niizhet Dalfes of the Department of Geology of ZTU for reviewing the manuscript.

REFERENCES

Amanatidis, G. T., Paliatsos, A. G., Repapis, C. C. and Bartzis, J. G. 1993. ‘Decreasing precipitation trend in the Marathon area, Greece’, Int. 1

DIE. 1994. istatistiklerle Tiirkiye, Devlet lstatistik Enstitiisii, Ankara, 150 pp. (in Turkish.) Erdogan, F. 1989. ‘T’ikiye’de yaygin kurakliklar’ TMMOB Meteoroloji. Muhendisleri Odasr Bulteni, Ankam, 2 , 1 4 . (in Turkish.) ErinC, S. 1969. Klimatoloji ve Metoaian, Istanbul Universitesi Cogaafya Enstitiisii, Istanbul, 35, 538 pp. (in Turkish.) Folland, C. K., Karl, T. R., Nicholls, N., Nyenzi, B. S., Parker, D. E. and Vinnikov, K. Y. 1992. ‘Observed climate variability and change’, in

Climate Change 1992: The Supplementary Report to the Intergovernmental Panel on Climate Change, Scientific Assessment, cambridge University Press, Cambridge, pp. 135-170.

Glantz, M. H. 1987. ‘Drought, famine and the seasons in Sub-Saharan Africa’, in Climate and Human Health, Proceedings of the Symposium in Leningmd, Vol. 1 ., WCAP-No., 1, World Meteorological Organization, Geneva, pp. 21 7-232.

Climatol., 13, 191-201.

1076 M. TURKES

Jacobeit, J. 1995. ‘Atmospheric circulation changes due to increased greenhouse warming and its impact on seasonal rainfall in the Mediterranean area’, in Draft Papers of the Regional Workshop on Climate Variabiliv and Climate Change, Vulnembiliry and Adaptation. Variabiliv of Circulation, Praha, 11-16 September 1995.

Kadioglu, M. 1993. ‘Ttirkiye’de iklim degi$kligi ve olasi etkileri’, Cevre {oruma (Environmental Profecfion). istanbul, 47, 3 6 3 7 . (in Turkish.) Koqrnan, A. 1993. Turkiye Iklimi, Ege Universitesi Edebiyat Fakiiltesi, Izmir, 83 pp. (in Turkish.) Kraus, E. B. 1977. ‘Subtropical droughts and cross-equatorial transports’, Mon. Wea. Rev., 105, 1009-1018. Nicholson, S. E. and Palao, I. M. 1993. ‘A re-evaluation of rainfall variability in the Sahel. Part I. Characteristics of rainfall fluctuations’, In?. 1

Climafol, 13, 371-389. t)z.giirel, M. and Koqman, A. 1994. ‘Ege Bolgesi kurakligi ve onlenrnesi iqin bulut tohumlamasi’, I. Ulusal Hidromefeoroloji Sempozyumu,

Istanbul Teknik Universitesi, Istanbul, pp. 20-3 1 . (in Turkish.) Repapis, C. C., Mantis, H. T. and Metaxas, D. A. 1989. ‘A study of the climatic variations in the eastem Mediterranean during the first half of

the 20th century’, Proceedings of the International Seminar on Climatic Flucfuations and Water Management, Cairo, 11-14 December 1989. Rodhe, H. and Viji, H. 1976. ‘Trends and periodicities in East African rainfall data’, Mon. Wea. Rev., 104, 307-315. Shinoda, M. 1990. ‘Annual rainfall variability and its interhemispheric coherence in the semi-arid region of Tropical Africa: Data Updated to

Singh, V P. 1992. Elementav Hydrologv, Prentice-Hall, New Jersey, 973 pp. Sneyers, R. 1990. On the Statistical Analysis of Series of Observations, WMO Technical Note 143, World Meteorological Organization, Geneva,

Sneyers, R. 1992. ‘Use and misuse of statistical methods for the detection of climatic change’, in Climate Change Detection Pmjecf. Report on

Srikanthan, R. and Stewart, B. J. 1991. ‘Analysis of Australian rainfall data with respect to climate variability and change’, Aust. Mefeorol. Mag.,

Toros, H., Deniz, A. and Karan,,H. 1994. Bat1 Anadolu yagylannin istatistiksel olarak incelenmesi’, I. Ulusal Hidrometeomloji Sempozyumu,

TSMS. 1989. Climatic Atlas of Turkey, Thrkish State Meteorological Service, Ankara. Tikep, M. 1990. Z‘urkiye ife Kumk Bolgeler ve h e m l i Ku.rak YI llar (Arid Regions and Considerable Dry Years in Turkey), Istanbul Universitesi

Deniz Bilimleri ve Cohafya Enstitiisii, Doktora Tezi, Istanbul, 195 pp. (in Turkish.) Tikes, M. 1995a. ‘Tiirkiye’de yillik ve mevsimlik yagip verilerindeki egilimler ve dalgalanmalar’, Turkiye Ulusal Jeodezi ve Jeofizik Birligi

(TUJJB) Bilimsel Kongresi, 3-5 Maps 1995, Ankara. (in Turkish.) Tikep, M. 3995b. ‘Trends and fluctuations in annual and seasonal rainfall data in Turkey’, in Draft Papers of the Regional Workshop on

Climate Variability and Climate Change Vulnerability and Adaptation, Temperature and Precipitation Variability, Praha, 1 1-1 6 September 1995.

1987’, I990 Japanese Progress in Climatology, Japan Climatology Seminar, pp. 98-107.

192 pp.

the informal Planning Meeting on Sfatistical Procedures for Climate Change Detection, WCDMP, 20, pp. 576-581.

39, 11-20,

Istanbul Teknik Universitesi, Istanbul, pp. 185-198. (in Turkish.)

WMO. 1966. Climatic Change, WMO Technical Note, 79, World Meteorological Organization, Geneva, 79 pp. WMO. 1988. Analyzing Long Time Series of Hydrological Data with respecf to Climate Yariabiliv, h j e c f Description, WMO/TD 224, World

Meteorological Organization, Geneva.