Tree-ring reconstructions of precipitation and streamflow for north-western Turkey

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1 INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 8: (8) Published online June 7 in Wiley InterScience ( DOI:./joc.5 Tree-ring reconstructions of precipitation and streamflow for north-western Turkey Ünal Akkemik, a * Rosanne D Arrigo, b Paolo Cherubini, b,c Nesibe Köse a and Gordon C. Jacoby b a Istanbul University, Forestry Faculty, Forest Botany Department Bahçeköy-Istanbul, Turkey b Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, 6 Route 9W, Palisades, New York, USA c WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland ABSTRACT: We describe tree-ring reconstructions of spring (May-June) precipitation and spring-summer (May-August) streamflow for north-western Turkey, both beginning in AD 65. These are among the first such reconstructions for the region, and the streamflow reconstruction is among the first of its kind for Turkey and the entire Middle East. The reconstructions, which both emphasize high-frequency variations, account for 34 and 53% of their respective instrumental variance. Comparison to precipitation and runoff data provides some means of verification for the instrumental streamflow record, which is very short (3 years). Drought and flood events in the reconstructions are compared to historical archives and other tree-ring reconstructions for Turkey. The results reveal common climatic extremes over much of the country. Many of these events have had profound impacts on the peoples of Turkey over the past several centuries. Copyright 7 Royal Meteorological Society KEY WORDS precipitation; streamflow; drought; reconstruction; tree rings; dendroclimatology; Turkey Received 8 March 6; Revised 9 February 7; Accepted February 7. Introduction Over the past few decades, there have been a number of severe and/or persistent drought and heat episodes in the countries bordering the Mediterranean, including Turkey (Luterbacher et al., 4; Pauling et al., 6). Such extreme events can have disastrous consequences for human society due to resulting famine and disease, soil degradation, desertification, and increased incidence of wildfires (di Castri and Mooney, 973; Le Houérou, 996). Since the major rivers of Turkey provide water for adjacent countries of the Middle East, fluctuations in Turkey s precipitation and streamflow can have wide-ranging geopolitical consequences. Meteorological records that provide information on climate variability are short and scarce for Turkey and for the Middle East as a whole(türkes, 996; Türkes and Erlat, 3). Extended climate records for Turkey are thus critically important for evaluating the spatial and temporal variability of extreme drought and flood events. Tree-ring records have yielded valuable information on past precipitation variability for many moisture-limited areas of the globe, augmenting available meteorological data (e.g. Jacoby et al., 976; Stahle et al., 985; D Arrigo and Jacoby, 99; Chbouki et al., 995; Meko et al., 995; Puigdefabregas and Mendizabal, 998; Cook et al., 4). For Turkey and surrounding areas of the * Correspondence to: Ünal Akkemik, Istanbul University, Forestry Faculty, Forest Botany Department, Bahçeköy-Istanbul, Turkey. uakkemik@istanbul.edu.tr Middle East, however, there have been relatively few such studies, although this situation has improved considerably in recent years (e.g. for Turkey: D Arrigo and Cullen, ; Hughes et al., ; Touchan et al., 3; Akkemik and Aras, 5; Akkemik et al., 5; Touchan et al., 5a,b; and for Jordan: Touchan and Hughes, 999; Touchan et al., 999). These recent efforts have focused mainly on reconstructing seasonal or annual indices of precipitation, or on investigations of anomalous climate years. For example, D Arrigo and Cullen () reconstructed precipitation for Sivas, north central Turkey. Hughes et al. () found that extreme signature years in tree-ring data from the Aegean region (including northern Turkey, Greece and Georgia) coincided with recorded April June precipitation and sea level pressure anomalies. Touchan et al. (3, 5a) demonstrated correspondence between Turkish tree-rings and atmospheric circulation patterns during extreme years. Although Touchan et al. s study partly overlaps that reported herein, they did not include data from our immediate north-western Turkey study region. Akkemik and Aras (5) described a tree-ring study for southern inner Anatolia, a region that, although not far from our study area, is very different ecologically and climatically from that investigated herein. For north-western Turkey, Akkemik et al. (5) presented a preliminary March June precipitation reconstruction based on instrumental station data. Unlike this previous work, our present study encompasses a much wider area of northwestern Turkey, is based on a different climatic season, and uses a larger tree-ring data-set. Copyright 7 Royal Meteorological Society

2 74 Ü AKKEMIK ET AL. The present study also differs from the previously cited efforts on Turkish dendroclimatology cited above in that it includes a reconstruction of streamflow. Treering based reconstructions of streamflow can yield much valuable information for planning of water resources (e.g. Stockton and Jacoby, 976; Pederson et al., ). Existing streamflow records in Turkey are generally very short; most are less than 5 years. For the Filyos river basin studied below, the streamflow record is only 3 years in length. Despite their limited length, such streamflow records for Turkey have proven useful in evaluating, for example, the impact of the North Atlantic Oscillation (NAO) on Tigris Euphrates streamflow (Cullen and demenocal, ), and mid-latitude streamflow responses to the extreme phases of El Nino Southern Oscillation (ENSO) (Kahya and Karabork, ). To our knowledge, no tree-ring reconstructions of streamflow have yet been developed for Turkey, although such records would be extremely useful. Here we present a reconstruction of spring (May June) precipitation for north-western Turkey, extending from AD 65. We also describe a reconstruction of streamflow extending over this same period, which is to our knowledge the first published for Turkey and one of the first for the entire Middle East. We expect that both reconstructions will be of considerable value for hydrological modelling and strategic water management planning for Turkey and adjacent countries. The goals of the present study are therefore: () to describe a new tree-ring data network of climatically sensitive chronologies for the western Black Sea region of north-western Turkey, () to reconstruct and analyse precipitation and streamflow variables using these chronologies, and (3) to compare these new reconstructions to other Turkish climate reconstructions and historical data archives for Turkey, specifically with regards to identification of large-scale drought and flood extremes.. Description of the Region.. General description The climate of Turkey is largely Mediterranean, with impacts from both higher latitude (temperate to subpolar) and lower latitude (tropical and subtropical) air masses. There are also continental and maritime influences on the region. For example, continental tropical air streams from the northern African and Arabian deserts often dominate throughout the summer, causing persistent hot, dry conditions over much of Turkey. Maritime effects arise from the proximity of the continental seas (Black Sea, Caspian Sea and the Mediterranean Sea, as well as the Atlantic Ocean, which can be sources of precipitation derived from mid-latitude cyclones (e.g. Turkes, 996; Cullen and demenocal, ). The NAO is an additional factor that impacts the climate of Turkey (e.g. Cullen and demenocal, ). The Northern Anatolia and Taurus Mountains, separated by the central Anatolian plains, extend in an eastwest direction parallel to the Black Sea and Mediterranean coasts to the north and south of Turkey, respectively. These mountain ranges are a principal factor influencing ecological conditions over much of Turkey. In north-western Turkey there are cold winters and the climate is generally humid; however it is drier (semihumid), with a moderate water deficit, during the warmer growing season months (Tatli et al., 4). Thus, moisture availability appears to be the dominant variable limiting tree growth, although temperature may also be a factor, particularly at higher elevation sites such as those studied herein. At the higher elevations (>7 m. a.s.l) of our study region, evergreen trees include species of pine (Pinus nigra Arn., Pinus sylvestris L.), fir (Abies bornmuelleriana Mattf.), yew (Taxus baccata L.), and juniper (Juniperus communis L. subsp. nana Syme., and J. excelsa Bieb.). At lower elevations, Pinus brutia Ten. is found, along with broadleaf species including oak (Quercus robur L., Q. petraea (Matt.) Liebl., Q. frainetto Ten.), beech (Fagus orientalis Lipsky), hornbeam (Carpinus betulus L.), alder (Alnus glutinosa L. (Gaertn.)), ash (Fraxinus excelsior L.) and elm (Ulmus minor Mill.). These trees are found in natural, unmanaged closed-canopy forests (Avci, 998). The forest types are zoned by elevation: dry forest between 5 m, humid-temperature forest between 5 m, and cold-humid forest above m (Yalcin, 98; Ozalp, 99; Avci, 998). Information on tree growth and past climate in this region is rather limited, and few dendrochronological analyses of past climatological conditions have yet been published... Hydroclimatology of north-western Turkey and the Filyos River basin The tree-ring sites studied herein lie within the Black Sea climate zone for Turkey, and also border the central Anatolia and Marmara Sea regions (Figure ). As defined in Unal et al. (3), the Black Sea region features a mean annual temperature of 3.7 C (SD.7 C) and a total mean precipitation of 75.8 mm (SD 5.5 mm). The climate type changes from semi-humid to very humid over the study region (Figure ). Partly due to the mountain ranges that parallel the shore, the western Black Sea region can be divided into three climate zones: i.e. north (very humid), central (humid) and interior (semi-humid) (Atalay, 983). The Bolu district represents the interior part of the western Black Sea region. Eskisehir is in a transition zone, with a climate closer to that of central Anatolia and the semi-humid climate type. The Kastamonu area, in the northern mountains (Küre mountains), features a very humid climate type (Figure ). The Filyos River is the principal river of the study region. It has four branches: Soganli, Arac, Filyos and Devrek. In all, the highest streamflow levels occur Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

3 TURKISH PRECIPITATION AND STREAMFLOW RECONSTRUCTIONS 75 Figure. Map of north-western Turkey showing locations of tree-ring sites (green one) used to reconstruct precipitation and streamflow, precipitation grid (box outlined in red), stations (in brown) and streamflow gages (in blue). This figure is available in colour online at Precipitation (mm) Eskisehir Ankara Bolu Kastamonu Precipitation Temperature Months Months Months Months Temperature (C ) Figure. Climograms for Eskisehir, Ankara, Bolu and Kastamonu. Water deficit during summer is higher in the interior of the region than near the coast. during April. Streamflow levels decline after May, with the lowest flows during August September. The annual total streamflow in the Filyos River system is.96. m 3 /year; from May August it is 96. m/ year, which is 8% of the total annual streamflow (Avci, 998). In the lower basin of the Filyos River, annual temperature is about 3 C, decreasing to 7 C in the upper Filyos basin. Annual precipitation in coastal areas is about mm, whereas in the inner parts of the basin it decreases to 5 mm. Precipitation occurs throughout the year, with a sizeable amount (3%) during winter. At lower elevations, the number of snowy days is low (about days); at higher elevations (above 5 m) snow cover is present during about 4 months of the year (Avci, 998). 3. Data and Methods 3.. Sampling and chronology development Pine (Pinus nigra and P. sylvestris) andfir(a. bornmuelleriana) trees were sampled at three sites for the analyses performed herein (Figure ). Three additional chronologies were also included in our analyses: two oak chronologies (Quercus spp., PIN; Akkemik et al., 5) and QUHA (Zonguldak Yenice) built by Kuniholm, P.I., Cornell University, and one pine chronology (TIR). A total of 54 cores from 5 trees were used (Table I). Samples were collected from sites near the towns of Bolu, Karabük and Kastamonu (Figure ). Site information, including latitude and longitude, slope, and length of chronologies, core/tree number, mean sensitivity and Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

4 76 Ü AKKEMIK ET AL. Table I. Site information for standardized tree-ring chronologies. Site/Chro.Names Elevation (m) Latitude (N) Longitude (E) Aspect Slope (%) Chronology period Core/Tree number Mean sensitivity c Correlation with their mean d PS South 4 8 9/..59 PS East /.3.74 AB East /..74 TIR Northeast /.7.67 PIN a West 6 59/4..56 QUHA b TOTAL 54/5 a stem discs were taken from a forestry centre and were obtained from historical buildings (Akkemik et al., 5). b This chronology, developed by Dr. Peter I Kuniholm, was obtained from the International Tree-Ring Data Bank. c Mean sensitivity is defined as the magnitude of changes in ring width from one year to the next. About. or high may be considered to be sensitive. d These series and site mean chronologies were standardized (we used the high- frequency or residual version derived in ARSTAN); these correlations indicate good agreement between individual series and their means. indicates 99.9% confidence level. mean site correlations, is listed for each of the six sites in Table I. Site elevations are generally at around m or above. Coniferous species typically grow at these altitudes, and broad-leaved species at lower elevations. The slopes range from to 8%, and are generally 4 6%. The mean correlation between site chronologies is.4, and the correlations of standardized individual series with the site mean chronology range between.56 and.76 withameanof.67(tablei). The chronologies used in the final reconstructions below were selected on the basis of the strength of the relationships between tree-ring widths and climate data. Annual ring widths were measured to a precision of. mm. The program COFECHA was used to test the accuracy of visual crossdating and measurement of ring widths (Holmes, 983; Grissino Mayer et al., 996). Each individual ring-width series was standardized with negative exponential or linear regression curve fits in order to remove non-climatic trends due to age, size, and stand dynamics (Fritts, 976). Standardization was performed using the ARSTAN program (Cook, 985; Grissino Mayer et al., 996). The detrended data from individual tree cores were combined into site chronologies using a bi-weight robust mean (Cook et al., 99a,b). When outliers (i.e. abnormal narrow and wide rings caused by individual factors except climate) are present, the arithmetic mean is no longer a minimum variance estimate of population mean, and may be biased (Cook et al., 99a). The bi-weight robust mean minimizes the influence of outliers, extreme values or biases (e.g. from spurious trends) in tree-ring indices (Cook et al., 99a). The ARSTAN program produces three versions of standardized chronologies: Residual, Standard and Arstan. The Residual, or RES chronology, was utilized herein as we have focused in this paper only on the interannual, or high-frequency climate signal (Cook, 985; Cook and Kairiukstis, 99; Figure 3). The RES version results from removal of the modelled autoregressive component from the detrended raw measurement series, and is thus primarily an indication of high- frequency (interannual) variability (although there are some indications of decadal variations; see Figures 4 and 6 below). Consistently, there is little persistence in either the instrumental precipitation or streamflow data used in this study (autoregressive orders are zero in both cases (Cook and Kairiukstis, 99). The RES chronology yielded the strongest correlation with May August streamflow (r =.74). However, we acknowledge by using the RES chronology that any information on longer-term (multidecadal) trends is removed. Lower-frequency variability in the tree-ring data will be the focus of a future study. We used the expressed population signal (EPS), which represents the degree to which a particular sampling portrays a hypothetically perfect chronology (Wigley et al., 984; Briffa and Jones, 99), as a guide in evaluating chronology reliability. An EPS value of.85 is a widely accepted threshold for adequate sample size in chronology development. The chronologies used in the reconstructions below were therefore truncated prior to 65, based on this threshold value. The EPS is calculated as follows: EPS = tr bt tr bt + ( r bt ) where t is the number of tree series averaged one core per tree- and r bt is the mean between tree correlations. 3.. Meteorological data and analyses Four station records (Bolu, Ankara, Kastamonu, Eskisehir) were compared herein to the tree-ring chronologies. The station data includes both monthly total precipitation and monthly mean temperatures. The four precipitation data-sets were screened for inhomogeneities using double-mass analysis, a graphical technique (Kohler, 949). A Potter s T-test (Potter, 98) was used to screen the temperature data for the four stations. The longest Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

5 TURKISH PRECIPITATION AND STREAMFLOW RECONSTRUCTIONS 77 PS 6 4 PS 6 4 AB 6 4 EPS>.85 QUHA 6 4 PIN 8 4 tree-ring index TIR Years number of samples Figure 3. RES tree-ring width chronologies used to reconstruct precipitation and streamflow for north-western Turkey. The date 65 (indicated by vertical line) indicates that based on the EPS cut-off of.85 the chronologies are reliable after that date. Streamflow (m/sc) O N D J F M A M J J A S Months Figure 4. Mean monthly streamflow data for the Filyos river over station data covers the years Some of our chronologies end in ; thus the analysis was performed over a 7 year period (93 ; year is lost due to consideration of lag effects). We ultimately, however, used gridded precipitation data for our final analyses because it showed higher correlations with the tree-ring data than the station records, and because it provides a more regional signal than the station records. This gridded monthly instrumental precipitation (and temperature data) was obtained from the Climatic Research Unit (CRU), East Anglia, UK ( 5 5 ) for northern Turkey for 93 (averaged over 39 4 N, 9 35 E) (Figure ). This website describes the quality control and homogenization procedures utilized in generating this gridded data as described in Legates and Willmott (99); Hutchinson (995); Easterling et al. (996); Hulme and New (997). Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

6 78 Ü AKKEMIK ET AL. Table II. Site information for streamflow gage data. River/Stream Gage Site Name Elevation (m) Latitude (N) Longitude (E) Soganli/Soganli Mengen/Gökcesu Arac/Karabük Filyos/Devecikvaran Monthly streamflow data (evaluated for quality control by Göktürk, 5) was obtained for the Filyos River in the western Black Sea region, covering , from the General Directorate of Electrical Power Resources Survey and Development Administration, Turkey (Table II). We selected the Filyos River data for the streamflow reconstruction because it is the dominant river in the region, and because its stream gage site is at the end point of the river and is thus representative of streamflow over a broad area. Mean annual streamflow is m 3 /s, and 8 m 3 /s during May August. The highest flow is in April at 33 m 3 /s, and the lowest in September at 3 m 3 /s (Figure 4). In dendroclimatology, data are typically divided into two for calibration and verification. For this study, however, the streamflow data is extremely short (only 3 years) and there is only enough data for use in the calibration of the tree-ring model. Instead, we have attempted to validate the streamflow reconstruction using the precipitation data over the same period (May August). We have also performed additional validation by comparing run-off data with the reconstruction. As another means of validation, the recorded and reconstructed precipitation and streamflow indices were compared to historical accounts and other tree-ring records for Turkey. To analyse extreme dry and wet events, empirical thresholds for dry and wet events were defined as 85 (86 mm) and 5% (6 mm) of the 93 to mean observed May June precipitation, respectively. This method has been used previously in dendroclimatological reconstructions for Turkey (Touchan et al., 3, 5a,b). 4. The Precipitation and Streamflow Reconstructions 4.. Precipitation reconstruction We first screened the tree-ring width chronologies in correlation analysis with the mean monthly temperature and precipitation (station and gridded) data from October of the year prior to growth (t ) to September of the current growth year (t). The strongest correlations were found between the chronologies PIN, QUHA, PS and TIR and spring (May June) precipitation for the gridcells from 39 4 N to 9 35 E (Figure 5). The trees also showed some correlation with temperature during the months of January April, which is not surprising as the region is both humid and cool. Based on Correlation coefficients O- N- D- J F M A M J J A S Months U_OA K_R PS R K_OA KR TIR R Figure 5. Correlation coefficients between the selected chronologies and total monthly precipitation; months with grey bars were used in reconstruction. May-June PPT (mm) 8 Estimated May-June PPT (mm) Recorded May-June PPT (mm) Years Figure 6. Comparison of recorded and estimated May June precipitation (for 39 4 N, 9 35 E) for common period from 93 to. This figure is available in colour online at wiley.com/ijoc these results, these four chronologies were selected to reconstruct the gridded May June precipitation record using principal components regression analysis (Cook and Kairiukstis, 99). A nested regression procedure (Cook et al., ) was employed in order to optimize the length of the reconstruction. This method involved using two nests, one based on all four chronologies from 8 to and the other based on the three longest series which date back to 65. These nested reconstructions were then spliced together after adjustment of the older nest (beginning in 65) to the mean and variance of the more recent and best replicated nest (beginning in 8). A split calibration-verification scheme was employed to test the reliability of the precipitation reconstruction (Table III; Figure 6; Cook and Kairiukstis, 99). The period from 93 to 958 was used for calibration and 959 for verification; this process was then reversed. Statistics used to test the reliability of the reconstruction models included the reduction of error (RE) and coefficient of efficiency (CE) statistics, the Sign Test, and Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

7 TURKISH PRECIPITATION AND STREAMFLOW RECONSTRUCTIONS 79 Table III. Calibration and verification statistics for precipitation (P ) and streamflow (S) nested reconstructions. Model Calibration Verification ar RE/CE ST P Precipitation % %.8/ /3 (.4).58 (.) %.39/ /4 (.).74 (.) % %.38/ /3 (.4).63 (.) %.45/ /4 (.).74 (.) Streamflow % 3 + /8 (.5).6 (.) % 7 + /4 (.).73 (.) % 7 + /4 (.).74 (.) ar, variance accounted for by tree-ring models, adjusted for degrees of freedom; RE, Reduction of Error; CE, Coefficient of efficiency; ST, Sign Test; P, Pearson s correlation coefficient. ST for streamflow is for the calibration period only. The Sign Test (ST. Fritts, 976) indicates the number of times there is agreement in sign between the actual and estimated data (number of positive values) versus the number of times when the two series are of opposite sign (number of negative values). The values in the parantheses show confidence level of ST. the Pearson s correlation coefficient (Fritts, 976; Cook and Kairiukstis, 99; Fritts et al., 99; Cook et al., 999). Both the RE and CE, but particularly the CE, are rigorous statistics for which any positive value indicates useful information in the reconstruction, but for which there is no significance level per se (Cook and Kairiukstis, 99; Fritts et al., 99). Both the RE and CE are strongly positive for both of the calibration periods, indicating considerable validity in the reconstruction models (Table III). Precipitation data for the full 93 period was then used to calibrate the final reconstruction (Figure 7). The final spring precipitation reconstruction, which explains 34% of the variance for the most replicated nest and extends from AD65, is shown in Figure 8. Additional validation of the reconstruction was obtained by comparison of the recorded and estimated drought years, here defined as those that exceed a threshold of one standard deviation. During 93, 78% (4/8) of the drought years in both the actual and reconstructed May June precipitation were found to agree (two of these did not exceed this threshold). Estimated May-June PPT (mm) Years Figure 7. Reconstruction of May June precipitation from 65 to AD. Standard deviation thresholds and 3 year low-pass filter values also indicated. This figure is available in colour online at Streamflow reconstruction Significant correlations were found between May August Filyos River streamflow data and four chronologies (QUHA, AB, PS and TIR) over the common period (Figure 8). The mean of these four chronologies correlates with the streamflow data at r =.75; a nearly identical correlation (r =.73) was found between correlation coefficients K_OAK AB PS TIR -.4 m- a- m- j- j- a- s- o- n- d- j f m a m j j a s months Figure 8. Correlation coefficients between the selected chronologies and monthly streamflow; months with grey bars were used in reconstruction. Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

8 8 Ü AKKEMIK ET AL. this four-chronology mean and mean streamflow data at four stream gage sites (Filyos, Mengen, Arac and Soganli, Table II). These four streamflow sites are closely related (the mean correlation between them is.8;. level), and the headwaters of these four rivers are very close to three of the tree-ring sites (QUHA, AB, PS). As was done for precipitation, a nested approach and principal components regression (Cook and Kairiukstis, 99) were utilized in order to develop the streamflow reconstruction. Three nests were generated and then spliced together as each chronology left the data matrix: for (four chronologies), (three chronologies) and (two chronologies). 53% of the variance (ar ) was explained for the most replicated ( ) nest. Statistics for these models are indicated in Table III. Comparison between the recorded and estimated streamflow is shown in Figure 9, and the streamflow reconstruction (65 998) is presented in Figure. Since the Filyos streamflow record is very short ( ), formal verification of the reconstruction could not be performed. However, some validation of the model was obtained by comparing the recorded and estimated streamflow indices with the recorded precipitation data for the May August season. Correlations between the May August precipitation record (39 4 N, 9 35 E) and the recorded and estimated streamflow May-August Streamflow (m 3 /sec) Estimated May-August Filyos River Stremflow Recorded May-August Filyos River Stremflow Years Figure 9. Recorded and estimated streamflow data for the Filyos River for This figure is available in colour online at series are.65 and.55 respectively (both correlations are significant at the. level). In order to further test the validity of the streamflow data, the streamflow indices were compared to recorded flood events. Several accounts of floods are available for the past 5 years for the Bartin basin (which includes the Filyos River) for comparison to our streamflow reconstruction. According to these accounts, floods occurred in 975, 98, 989, 99, 995, 997 and 998 (Anonymous, 999). These floods typically correspond to aboveaverage years in our streamflow reconstruction. The greatest flood occurred in May 998, an event which is clearly evident in Figure 6. About 9% of the flood records were also observed in the reconstruction. This strong level of agreement thus provides additional validation of the streamflow reconstruction. 5. Drought and Flood Events for North-Western Turkey The precipitation and streamflow reconstructions reveal valuable information on the interannual climate variability of north-western Turkey over the past 35 years. Both reconstructions primarily emphasize high-frequency fluctuations, and thus decadal or longer-term trends in precipitation or streamflow were not retained in this analysis and were not discussed herein. In order to investigate extreme drought and flood events in the reconstructions, we used positive and negative anomaly thresholds, defined (as previously noted) as those exceeding 85 (86 mm) and 5% (6 mm), respectively (Touchan et al., 3, 5a,b). Using this criterion, we identified 6 dry and 35 wet events over the pre-instrumental (65 93) period in the precipitation reconstruction. Only events showed persistent dry anomalies that exceeded the 85% threshold for at least two years ( ; 77 78; 75 76; 73 73; ; 89 8; 87 88; 86 86; ; 97 98). There are no such events of 3 years or more. The longest interval between dry events is years (95 96), with a mean period between events of 5 years. As noted, the region is generally humid, and this observed duration of dry years is less than, for example, that found for the Mediterranean region (Touchan et al., 3). Estimated May-August Streamflow (m 3 /sec) Years Figure. Reconstruction of May August streamflow for the Filyos River from 65 to998. Standard deviation thresholds and 3 year low-pass filter values also indicated. This figure is available in colour online at Core numbers Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

9 TURKISH PRECIPITATION AND STREAMFLOW RECONSTRUCTIONS 8 The frequency of dry years is about the same with the Mediterranean region, where Touchan et al. (3) computed a mean drought recurrence interval of 4.8 years. For most of Turkey, Touchan et al. (5b) computed a mean recurrence interval of dry events of 3. years, with the longest dry events lasting 5 years (based on tree-ring data from north-eastern Turkey and the Mediterranean and Aegean regions). Our reconstruction, for more humid north-western Turkey, thus indicates a shorter (only year) duration for dry events. However, due to differencesinmethodology thetouchanet al. results may not be directly comparable to those computed herein. The precipitation reconstruction includes 36 one-year wet events during Longer events were again rare, with only two year events (in and 86 87). The maximum interval between wet events is 7 years (784 8), with a mean of 8 years.the results for the streamflow reconstruction are very similar to those for precipitation and are not further described. 6. Comparison with other Turkish Reconstructions and Historical Archives Table IV compares extreme dry and wet years identified in our reconstructions with those found in other tree-ring reconstructions and chronologies for Turkey (Kuniholm, 996; D Arrigo and Cullen, ; Touchan et al., 3, 5a,b; Akkemik and Aras, 5; Akkemik et al., 5 and Hughes et al., ), as well as historical archives (Purgstall, 983; Panzac, 985; Ottoman Archives of the Prime Minister of Turkey, 85 93; Inalcik, 997). Only one other tree-ring reconstruction (Touchan et al., 3) covers the same months (May June) as our precipitation reconstruction. Despite differences in seasons, methodology, and site locations, however, there is reasonably good agreement among the various reconstructions, which together cover much of Turkey. The various reconstructions have in common 3 drought years and wet years. A number of significant climate events are associated with catastrophic historical and cultural changes over the 35 year length of our reconstructions. For example, major drought and famine events occurred around Anatolia and Syria in and , according to historical records (Panzac, 985). Thousands of people emigrated from Cyprus as a result of the 757 drought and famine (Inalcik, 997). Kuniholm (99) described a catastrophic drought in Turkey from 873 to 874, based on historical accounts in Christiansen Weniger and Tosun (939) and Naumann (893). According to these latter records, a drought in the province of Ankara, central Turkey, in 874 was of such devastating proportions that 8% of the cattle and 97% of the sheep died. Hunger and sickness during the winters of killed more than people (Naumann, 893). A cholera outbreak in Iran in 89 (Afkhami, 998) may have resulted at least in part from drought conditions (D Arrigo and Cullen, ). Wheat exports were prohibited because of drought-related shortages, and tons of Table IV. Extreme dry and wet years in the reconstructions and their comparison with those identified in historical accounts and other tree-ring reconstructions for Turkey. 7th century 8th century 9th century th century Dry events 66,,4,6 7,4,6 757,4,5,6,c,d 8, ,a 67,,4 77,6 764,,3,4 85,3,5 875,6 97,,3,4,5,6,a,b 676,,3, ,3, ,,3,4,5,6,7,a,b 98,,3,4,5,6,7,a,b 687,4,6 75,,4,5,6 78,,3, ,,3,4,5,a ,,3,4,5,6,d , ,5,6 73,3 797,5,6 84,,3,4, ,,3,4,5,6 849,4 748 Wet events ,,3 8,6 87,5,6 9,,3,4,5,6, ,,3, ,, ,,3,4,5,6 76,4,6 86,,3,4,6,e 88,,3,4,6,7 96,,4,6 689,,3,4,5, ,4, ,,4,5 9,4,6,7 7 3,6 77,,3,4,5, ,,3,4,5,7 97,3,4, ,,3,4, ,5 77,,3,4,5, ,6 Events also observed in the streamflow reconstruction; Comparison of precipitation reconstruction is made with tree-ring reconstructions by ) Touchan et al. (5a), ) Touchan et al. (5b), 3) Touchan et al. (3), 4) D Arrigo and Cullen (), 5) Akkemik and Aras (5), 6) Akkemik et al. (5), 7) Kuniholm, 996 and Hughes et al., ; and with historical documents from a) Ottoman Archive, b) Purgstall (983), c) Inalcik (997), d) Panzac (985). Copyright 7 Royal Meteorological Society Int. J. Climatol. 8: (8) DOI:./joc

10 8 Ü AKKEMIK ET AL. wheat were sent from storage to the provinces in the years 854, 867, , 887, 89 89, 893, 94 95, 99, and (Ottoman Archive: 85 93). The years 854, 867, , 89, 95 and 99 were below average in the precipitation reconstruction, but not significantly so. Since cold temperatures, not drought, are believed to have been the primary cause for the winter famine, extreme drought years might not be expected in the reconstruction in these years, as suggested by the reconstructions. Both reconstructions, but especially the streamflow reconstruction, reveal a persistent drought event in the last decades of 9th century overlapping with droughts in 887, 89, 89 and in the historical documents. The years of highest streamflow values, which also coincide with extremely high precipitation, are reconstructed for and 97, with values also above average in Consistent with this latter observation, there were reports of severe flooding around 95, when water levels reported to rise by 3 m (B. Yaman, Forestry Faculty of Bartin, pers. comm.). These comparisons thus indicate a number of instances in which there is correspondence between the tree-ring estimates for Turkey and historical documents of anomalous precipitation and streamflow events. 7. Conclusions The precipitation and streamflow reconstructions presented herein are among the first such records for Turkey and the Middle East as a whole. Although our study region of north-western Turkey features a more humid climate than most of the country, meaningful information on past moisture variability has nevertheless been obtained. The results presented herein are consistent with, and expand upon, those found for a preliminary reconstruction developed for the region based only on oak data (Akkemik et al., 5). As a result of the relatively humid climate, dry events appear to be of shorter duration than in other regions. However, it is important to note that since our reconstructions emphasized high-frequency variations, it was not possible to discern decadal and longer-term trends, which will be addressed in a future study. We have instead used the reconstructions to identify extreme high-frequency drought and flood episodes for north-western Turkey over the past 35 years. The observed relationships between the treering chronologies, precipitation and streamflow presented for this region are an encouraging indication of the future potential for such studies in Turkey. Our results are of particular interest as Turkey is one of the main suppliers of water for Syria and Iraq. Water availability is critically important for the drier areas of Turkey as well. The information provided herein on past drought and flood extremes should prove of much interest to researchers and modelers concerned with water management, hydrological forecasts and other applications. Acknowledgements This study was supported by the Scientific and Technical Research Council of Turkey (TUBITAK); project number TOGTAG-73; and the TUBITAK-NATO B- Fellowship Program of the same Council. Tree-ring data from some sites was obtained from the NOAA Paleoclimatology International Tree-Ring Data Bank (ITRDB). We thank Ozan Mert Göktürk and Rob Wilson for technical assistance. Some analyses were performed using KNMI Climate Explorer. Lamont Doherty Earth Observatory Contribution No. 7. References Afkhami A Disease and water supply: the case of cholera in 9th century Iran. In Transformations of Middle Eastern Natural Environments: Legacies and Lessons, Yale University Bulletin Series No. 3, Coppock J, Miller J (eds): New Haven, CT; 6. Akkemik U, Aras A. 5. Reconstruction ( ) of April- August precipitation in southwestern part of central Turkey. International Journal of Climatology 5: Akkemik U, Dagdeviren N, Aras N. 5. 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