A 250-year annual precipitation reconstruction and drought … · 2014. 1. 28. · INTERNATIONAL...

INTERNATIONAL JOURNAL OF CLIMATOLOGYInt. J. Climatol. (2013)Published online in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/joc.3869

A 250-year annual precipitation reconstruction and droughtassessment for Cyprus from Pinus brutia Ten. tree-rings

Carol Griggs,a* Charlotte Pearson,b Sturt W. Manninga and Brita Lorentzenaa The Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology, Cornell University, Ithaca, NY, USA

b LTRR, University of Arizona, Tucson, AZ, USA

ABSTRACT: Precipitation around Cyprus, a relatively small island, is generally consistent in year-to-year variation inall dimensions except amplitude, with the higher elevations in the west generally receiving more precipitation. An annualrecord of precipitation was found in tree-rings of the predominant pine species, Pinus brutia Ten., which grows from thelower foothills up to 1400 m in altitude across the island. Tree-ring chronologies from four sites in west-central Cyprus areused here to reconstruct the annual September to August precipitation and a drought record for AD 1830–2006, with thedrought reconstruction extending back to 1756. A minimum of 40% of the variance in annual precipitation and droughtoccurrence is explained by the variance in the tree-ring widths in all cases. Our drought assessment indicates that, onaverage, annual droughts occur once every 5 years and sustained droughts, 2–6 years in length, have occurred in smallclusters of time, from 1806–1824, 1915–1934 and 1986–2000, when the winter North Atlantic Oscillation was in apredominantly positive phase. These results suggest that a sustained drought period has a mean return time probability ofone in 70–100 years. This study provides the first long-term annual precipitation reconstruction and drought assessment atlow to mid-elevations for Cyprus and will aid in future plans for drought mitigation.

KEY WORDS annual precipitation reconstruction; drought record; dendroclimatology; Pinus brutia (Ten.); Cyprus; TroodosMassif; North Atlantic Oscillation

Received 25 February 2013; Revised 8 October 2013; Accepted 12 October 2013

1. Introduction

Past climate parameters have been reconstructed frommany proxy records developed to understand palaeocli-mate conditions over time around the world. The natureand quality of the reconstruction depend on the originof the data sets employed. For the time series in a den-droclimatological reconstruction the general principle isthat trees primarily respond to certain climate parametersduring their growing season months, particularly precip-itation in any drier region of the range of the studiedspecies, and temperature at high latitudes or altitudes(Hughes et al., 2011; Fritts, 1976). However, in Cyprus,the amount of precipitation occurring year round criti-cally influences water availability throughout the growingseason, so the trees contain an annual precipitation recordthat is unusual and of considerable importance in acquir-ing a more complete understanding of long-term climatechange in Cyprus and the northeastern Mediterraneanregion.

Cyprus is located at approximately 35◦N and 33◦E, atthe east end of the Mediterranean Sea, and is ∼224 kmWSW to ENE, and ∼97 km NNW–SSE with a land areaof approximately 9250 km2 (Figure 1). The island hastwo mountain ranges – the Troodos Massif (maximum

* Correspondence to: C. Griggs, The Malcolm and Carolyn WienerLaboratory for Aegean and Near Eastern Dendrochronology, B48 Gold-win Smith Hall, Ithaca, NY 14853, USA. E-mail: [email protected]

elevation 1951 m) in the southwest and the Pentadaktylos(Kyrenia) range (maximum height 1000 m) along thenorthern coast, which give Cyprus high topographicalvariability (Price et al., 1999).

Cyprus has a Mediterranean climate regime consistingof hot, dry summers with clear skies from June toSeptember, and cool, wet winters from November toMarch (Figure 2). The short autumn and spring seasonsin October, April and May are characterized by highvariability and rapid changes in precipitation and temper-ature (Price et al., 1999). The minimal cloud cover andhigh temperatures in summertime are largely influencedby the combination of subsidence from the northwardshift of the subtropical high and the Persian trough, ashallow low-pressure trough extending from the Asianmonsoon depression centred over Pakistan, which leadsto summertime northwesterly winds. When summerrainfall does occur, it is usually in the form of isolatedthunderstorms and contributes less than 5% of the totalannual rainfall. Winter weather is generally influencedby unsettled small low pressure systems crossing thesea from between the continental anticyclone of Eurasiaand the persistent low pressure belt over North Africa.These depressions produce the majority of the island’sannual precipitation, with the average precipitation fromDecember to February being about 60% of the annualtotal (Price et al., 1999) (Figure 2).

Unequal heating of the sea surface and island interiorplus a large variation in the island’s topography create

2013 Royal Meteorological Society

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Figure 1. Map of Cyprus showing study sites and weather stations on the Island. The cross-hair shows the centre of the 4 CRU 0.5◦ grids at33.0◦E, 35.0◦N.

Figure 2. Mean monthly precipitation totals and average temperature for Cyprus. Data is from the Cyprus Meteorological Service and the ClimateResearch Unit (CRU).

substantial seasonal and daily temperature differencesbetween these sites, resulting in localized climate varia-tion. The central Troodos Massif, and, to a lesser degree,the Kyrenia range also play an important role in definingthe weather conditions of Cyprus. Mean annual precip-itation increases up the south windward slopes to thetop of the Troodos range from 45 cm to nearly 110 cm,while on the leeward slopes amounts decrease steadilyto the north and east to around 30–35 cm (Price et al.,1999; Pashiardis and Michaelides, 2008). In the wintermonths snow may lie for several weeks at considerable

depths (ca. 1–1.5 m) on the high northern slopes, whilesnowfall is rare in the Kyrenia range and lowland areas(Pashiardis, 2000). However, despite variations in ampli-tude, precipitation across the island is fairly consistent inyear-to-year anomalies (Figure 2, Table 1) which allowsfor a stable precipitation reconstruction across the island.

Over the last half of the 20th century AD, availablemeteorological data indicate a general increase in tem-perature and a slight decrease in precipitation with acorresponding increase in drought (Price et al., 1999;Pashiardis and Michaelides, 2008). We show here that

2013 Royal Meteorological Society Int. J. Climatol. (2013)

A 250-YEAR PRECIPITATION AND DROUGHT RECORD FROM TREE-RINGS FOR CYPRUS

Table 1. October-September �P correlations between stationsand the average of 4 grids (CRU) for 1918–2008, with the

exception of Agios Epifanios, at 1957–2008.

Agios Epifanios

Troodos 0.693 TroodosPedoulas 0.697 0.866 PedoulasPano Panagia 0.569 0.841 0.843 Pano PanagiaPeristerona 0.779 0.570 0.592 0.561 PeristeronaAvg 4 grids(CRU)

0.793 0.649 0.754 0.670 0.697

the number of droughts and the extreme level of annualprecipitation during the droughts have not significantlychanged, but the variability and number of moderate tovery wet years is considerably reduced, especially in the1970s–1980s. This exacerbates the effect of droughtswhen they occur due to little or no groundwater replen-ishment from current and previous years. In the late 20thto early 21st centuries, drought in Cyprus has causedproblems ranging from support of a growing populationand tourist industry to sustaining the agricultural sector(especially viniculture). The severe drought of 2007/2008reduced reservoir supplies to just 3% of capacity (Dav-enport, 2008). Mitigation and management strategies areneeded, but such planning is inhibited by the fact thatmost of the ∼150 weather station records on the islandbegin around 1960 or later, with less than 25 extendingback to the early 1900s and even fewer having the unifor-mity necessary for a valid assessment. Our reconstructionextends the meteorological record by 160 years, nearlytripling the information necessary for planning droughtmitigation strategies. This data set also provides a morecomplete record of variation in precipitation over timeand space, in particular with respect to its relationship tothe low-frequency climate variation that is most evidentin seasonal data (Michaelides et al., 2009).

Pinus brutia Ten. (Calabrian pine) is a common low-land pine species in the eastern Mediterranean (Panetsos,1981; Quézel and Barbero, 1992) whose range stretchesfrom northeastern Greece, the Aegean Islands and Cyprusthrough the west and southern coasts of Turkey to Syria,Lebanon and Iraq (Panetsos, 1981; Boydak, 2004). Thespecies is thermophilous and prefers lowland semi-humidto humid sites with mean annual temperatures between12–20 ◦C (Quézel and Barbero, 1992; Boydak, 2004). InCyprus, P. brutia is the dominant tree species at eleva-tions from 0 to 1400 m in the Troodos and Pentadaktylosranges (Ciesla, 2004), making up over ca. 90% of theforested area of Cyprus during the last century (Thirgood,1981; Pantelas, 1986). Although its provenances varyphysiologically (Schiller, 2000; Boydak, 2004), P. brutiais generally extremely drought resistant, with a deep root-ing zone, and can grow in areas with mean annual rainfallas low as 400 mm (Nahal, 1983). It typically grows onmarls, limestone and dolomites and can tolerate volcanicsoils, but does not tolerate poorly drained soils (Quézel,2000). In optimum conditions and especially at the higherelevations with more precipitation, these trees can live

for over 500 years (Tsintides et al., 2002). Touchan et al.(2005) report finding P. brutia at elevations ranging from1483 to 1646 m at Armiantos, Cyprus, with lifespansof over 400 years. Our collection indicates a range of150–300 years is more normal for the species at the midand lower elevations, and Boydak (2004) reports a simi-lar age range (250–305 years) for P. brutia mainly at themiddle elevation range in southwestern Turkey. In bothareas human activity is a major factor, but climate condi-tions are also more stressful to tree growth than at higherelevations.

Immediately apparent in our exploratory analysis wasthe clear response of P. brutia ring-growth to annualprecipitation. This response is similar to a study bySarris et al. (2007) that showed evidence of significantlylower annual precipitation from 1985 to 2000 recorded inP. brutia on the island of Samos, Greece. The droughtyears of the Samos meteorological data correlate verywell with the Cypriot drought years, taking into accounttheir use of January to December precipitation rather thanour use of the precipitation from September to Decemberof the year before growth and January to August ofthe year of growth. Touchan et al. (2005) reconstructedMay to August precipitation on a much larger scale inthe northeastern Mediterranean region, including Cyprus,using many genera and species of conifers, includingP. brutia . However, it is not an annual record, and thedrought years indicated by both the meteorological dataand their reconstruction do not match many of the annualCypriot drought years in our data sets. The results ofKienast et al. (1987) indicate variability in the climateresponse of trees growing along altitudinal transects, withprecipitation the primary factor but increased sensitivityto temperature at the higher altitudes, especially in areaswith thin soil. Thus our observations and the previousstudies clearly indicate that P. brutia is a suitable speciesfor reconstructing Cypriot drought history.

We selected four study sites at varying elevationsthat were likely sensitive to rainfall variation (Figure 1,Table 2). The sites are located at ascending altitudesaround the Troodos Massif, underlain by the Troodosophilite and a mixture of non-calcareous eutriclithosolsand cambiosols. They are the Mitsero Hills area (MSH),the Roudhias Valley, Arodafna (RVA), Stavros tis Psokas(STV) and Doxa Soi o Theos (DST) (Figure 1, Table 2).The site at the lowest altitude, MSH, is northeast of theTroodos Massif on the edge of the Mesoria Plain incentral Cyprus, within the pillow lava zone around themountains, and is distinct from the other sites in that itis within the drier rain-shadow between the Troodos andPentadaktylos (Kyrenia) ranges.

2. Methods

At each site, up to three cores were sampled from eachtree at breast height (ca. 1.3 m) using a 5 mm incrementborer. Sections were also cut from available stumps atthe Roudhias Valley site. The cores and two to four radii


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Table 2. Description of site locations and sample collection.

Site Site code Elevationrange (m)

Latitude ◦N Longitude ◦E Yearsspanned

Totalyears

No. oftrees

No. ofcores /radii

Mitsero Hills MSH 485–498 35.034 33.094 1776–2009 234 20 42Roudhias Valley, Arodafna RVA 494–860 34.955 32.649 1633–2011 379 23 40Stavros tis Psokas STV 860–1132 35.037 32.639 1656–2006 351 24 53Doxa Soi o Theos DST 1328–1403 34.955 32.965 1637–2008 372 25 41

of the sections were prepared and measured accordingto standard dendrochronological procedures, using theTRiDaS compliant dendrochronological analysis pack-age – Tellervo (Brewer et al., 2010; Jansma et al., 2010).The ring-width series for each tree were combined. Foreach site, the tree-ring sequences were crossdated witheach other, and a site chronology was built. Crossdat-ing and data quality were checked using the programmecofecha 6.02 (Holmes, 1983).

The time series for each site was constructed usingarstan 41d_xp (Cook and Holmes, 1986). The tree-ringwidth measurements were detrended by fitting a negativeexponential curve when possible or, more often, a splinecurve with a 50% cutoff. Each year’s ring width wasdivided by the curve’s value in the same year to removelong-term non-climatic effects from age, tree size andstand dynamics (Fritts, 1976). The autocorrelation of theadjacent ring widths in each site’s standardized chronol-ogy was removed to make the residual chronologiesused here for the reconstructions (Cook and Kairiukstis,1990). We re-iterated arstan for each site chronology,choosing the option to test for unstable changes in thevariance of the ‘common signal’ in the representedsamples across the chronology. In this test, for eachperiod in the chronology over which there is no changein sample count, the average correlation (r-bar) iscalculated between all samples included in that periodover the full length of time represented by those samples(e.g. for the12 samples in one 10-year period, the r-bar iscalculated not for those 10 years, but for the total numberof years in common in these samples). Any significantchange in the r-bar values from one period to the nextrepresents a change in the strength of the commonsignal in the chronology which reduces its homogeneity,and requires an adjustment for a valid reconstruction(Briffa and Jones, 1990; Osborn et al., 1997). In ourfour site’s residual chronologies, we found no significantdifferences in the r-bars over the intended reconstructionperiods and used them in the reconstructions.

Monthly precipitation data for 19 stations wereobtained in 2012 from the Cyprus Meteorological Ser-vice, Ministry of Agriculture, Nicosia, Cyprus. The datasets, as well as gridded precipitation and temperaturedata sets in CRU TS 3.0 (Hulme, 1992, Mitchell andJones 2005; Climatic Research Unit, 2010 at http://badc.nerc.ac.uk/browse/badc/cru) were used to calculateanomalies for each month and for many annual andseasonal combinations. The length of the precipitationdata sets, the locations of the stations and each data set’s

homogeneity (Michaelides et al., 2009: Table 1) wereconsidered in choosing the data sets along the altitudinaland longitudinal transects. Their monthly precipitationanomalies (δP) were averaged into a single regional dataset. The values of the CRU precipitation and temperatureanomalies from the four 0.5◦ grids covering 32.5–33.5◦E, 34.5–35.5 ◦N (Figure 1) were also averaged togetherfor inspection over the study region. Since our focuswas on reconstructing precipitation variations anddrought, we used the temperature data mainly to testwhether it had any significant influence on the drought,precipitation and ring growth over time and space.

The Mitsero Hills chronology was used for a localprecipitation reconstruction due to the site’s locationin a low altitude, xeric environment. For the regionalclimate reconstruction, principal components (PC) werecalculated from the four site chronologies. The extendeddrought reconstruction back to 1755 used the twomiddle-elevation site chronologies. Initially, primarygrowth responses of all the tree-ring data sets to climateparameters were assessed from Pearson correlationsof the monthly climate data of the stations and regionversus the site chronologies and PCs. To find the transferfunctions suitable for reconstruction, stepwise multipleregressions were used in which each chronology orPC was the predictand and the monthly climate datawere the predictors in order to determine the climateparameters recorded in the tree ring growth. Additionalresponse functions used combinations of the monthlydata sets, ranging from seasonal to annual in length, aspredictors. The results were screened to determine thebest predictor(s). The resulting equations were examinedfor variations in the tree-ring growth response to climateparameters across the different elevations, from site tosite, and over time, to assess the spatio-temporal stabilityof the response and potential reconstruction.

Transfer functions were developed, in which the appro-priate tree-ring chronologies or PCs were the climatevariables identified from the regression analyses. Asplit-sample procedure, in which the models were dividedinto subsets of equal length, was also used to verifythe climate reconstruction model’s stability. For verifica-tion of the single-site reconstruction, the data sets weredivided into two periods, 1959–1983 and 1984–2009.For the regional precipitation and drought reconstruc-tion, the data was divided into three time periods from1918–1947, 1948–1977 and 1978–2006. The valid-ity of the resulting regression equations as accuratetransfer models was then evaluated with regression and



Table 3. Descriptive statistics for the samples and chronologies. The mean correlation among trees and the variance explained bythe first PCs are for 1830–2006.

Site code Standarddeviation

Skewness Kurtosis First year EPS>0.85a and n > 4

Mean correlationamong trees

First PCvariance (%)

MSH 0.32 −0.51 0.08 1820 0.762 66.9RVA 0.21 −0.21 0.37 1740 0.606 73.0STV 0.23 0.05 −0.05 1756 0.622 43.5DST 0.20 −0.48 0.29 1816 0.628 42.0aAn EPS value of >0.85 is arbitrarily significant (Cook and Kairiukstis 1990).

correlation statistics, including variance explained (R2)and reduction of error (RE; Cook and Kairiukstis, 1990).The PRESS statistic (Allen, 1974) was also used in val-idation, and was performed by leaving 5 years out itera-tively across the lengths of the calibration and verificationperiods (Table 5). A regression equation was calculatedfor each data set with the 5 years removed, then used tocalculate the predicted values for those 5 years. The 5-year predicted data sets were combined into a time serieswhich was then compared to the original reconstruction.The value of the residual sum of squares between the twotime series, divided by the length of the time series, isthe PRESS statistic, and the smaller the value, the moreaccurate is the model (Allen, 1974).

The final regression equations, successfully calibratedand verified, were used to reconstruct the local andregional precipitation for 1831–2006, and the droughtrecord for 1756–2006.

Finally, an assessment of the severity and frequency ofdroughts over time indicated by the reconstructions wasundertaken. We compared the reconstructions with sea-sonal subsets of the precipitation data (September throughNovember, December to February, March to May andJune through August) plus data sets of the North AtlanticOscillation (NAO; Hurrell, 1995, updated and availableat www.cgad.ucar.edu/cas/jhurrell/nao.stat.winter.html),and the East Atlantic Western Russia pattern (EAWR;Krichak and Alpert, 2005a, updated and available atftp://ftp.cpc.ncep.noaa.gov/wd52dg/data/indices/eawr_index.tim). An arbitrary 11-year running mean of eachdata set was used to emphasize low frequency variation.From this assessment we are able to cautiously predictfuture drought occurrence in Cyprus.

3. Results

3.1. The tree-ring chronologies and meteorologicaldata

Table 3 provides a summary of the statistics for theresidual tree-ring chronologies from each of the foursites – the Mitsero Hills area (MSH), 1776–2009;Roudhias Valley, Arodafna (RVA), 1633–2011; Stavrostis Psokas (STV), 1656–2006 and Doxia Soi o Theos(DST) for 1637–2008. The residual chronologies allcorrelate significantly with each other, with the valuesshowing an expected reduction in relation to the sites’altitudes and locations relative to each other and to

the Troodos Massif (Table 4). Outside of Cyprus, theMitsero Hills chronology correlates significantly with theP. brutia chronology of Atera in Syria at about the samealtitude, and the three site chronologies from the higherCypriot sites correlate significantly with that from Göllerin southern Turkey (Table 4).

A careful inspection of the homogeneity of monthlyprecipitation data from 13 weather stations established byMichaelides et al., (2009): Table 1) and the CRU griddeddata, plus the stations’ geographic locations, resulted intwo outcomes for the data sets used in this study. First,the precipitation data from Agios Epifanios, a stationclose to the Mitsero Hills, was truncated up to 1957 due tonon-homogeneity, and converted into anomalies. Second,we combined the monthly precipitation anomalies fromthree meteorological stations along a roughly east–westtransect across the Troodos Massif – Pano Panagiaand Pedoulas from higher altitudes, and the Peristeronastation also near the Mitsero Hills site (Figure 1) – for theregional precipitation data. All three data sets correlatesignificantly with each other (Table 1), begin in 1917,and are homogeneous for 1917–2009. The comparison ofthis precipitation data and those from all Cypriot stationsand the CRU gridded data indicated that the CRU data isbased mainly on precipitation data from several stationsat lower elevations around the island.

3.2. The annual precipitation record

Correlations and response functions between the sitechronologies and the monthly precipitation data sets indi-cated a consistent annual precipitation record. Especiallyevident was a high variability in the growth response toany one particular month, season or multi-season precipi-tation over time. The correlations and response functionsbetween the site chronologies and monthly precipita-tion data also indicated an altitudinal gradient in growthresponse (Figure 3). The high positive correlations withthe winter precipitation are with the chronology from thelow elevation Mitsero Hills site. At the higher sites thestrongest correlations were between tree rings and pre-cipitation during the growing season and in the previousautumn months when the amount of water available forthe next year’s growth starts to be replenished and isstored in the trees whenever photosynthesis is possiblefor P. brutia (Yaseef et al., 2010).

These results also indicated that only the P. brutia tree-rings from the lowest elevation site, Mitsero Hills (MSH),contain a clear record of annual precipitation (Pearson


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Table 4. Correlations between the four site tree-ring chronologies in this study, and between them and chronologies from othersites in Cyprus, Syria, and Turkey. Distances between sites are listed below the correlations. The bold values are at the p <0.005 significance level, the normal print at p < 0.05, and the italicized values are insignificant. The Stavros Psokas, Armiantos,NW Syria, and Göller (southern Turkey) chronologies were built by R Touchan, and the Stavros (mittel) and Planos Platres

chronologies by F Schweingruber. All are available at the ITRDB (2010).

MSHElev = 492m

RVA 0.38 RVAElev = 680m 43 km

STV 0.167 0.472 STVElev = 1000m 43 km 9 km

DST 0.194 0.297 0.523 DSTElev = 1365m 15 km 29 km 31 km

Stavros (mittel) 0.279 0.581 0.593 0.492 Stavros (mittel)Elev = 800m 43 km 5 km 4 km 32 km

Stavros Psokas 0.157 0.236 0.609 0.441 0.333 Stavros PsokasElev = 1050m 42 km 7 km 2 km 31 km 2 km

Armiantos −0.169 0.01 0.472 0.473 0.064 0.471 ArmiantosElev = 1550m 22 km 23 km 27 km 7 km 27 km 27 km

Plano Platres −0.026 0.092 0.321 0.479 0.154 0.43 0.576 Plano PlatresElev = 1620m 23 km 24 km 28 km 9 km 28 km 28 km 2 km

NW Syria 0.18 0.3 0.312 0.202 0.417 0.331 0.184 0.23 NW SyriaElev = 480m 278 km 319 km 317 km 292 km 320 km 318 km 298 km 299 km

Göller 0.073 0.261 0.355 0.392 0.316 0.431 0.343 0.307 0.103Elev = 1047m 324 km 304 km 296 km 323 km 298 km 297 km 322 km 323 km 512 km

Figure 3. Results of the response functions using the site chronologies and regional monthly precipitation data for the year before and the yearof growth. Grey horizontal lines represent a p < 0.05, and the dotted line has a p < 0.01. The vertical broken lines surround the months of

September through August, the sequence of months included in the annual reconstruction.

r = 0.784). This is a predictable response because averagelocal precipitation is around 400 mm year−1, a criticallevel for the species (Nahal, 1983), and the reason whythis chronology was chosen for the local precipitationreconstruction.

3.3. The reconstruction of precipitation and drought

The data from the Agios Epifanios station, located about5 km SSE of the Mitsero Hills site at approximately200 m higher altitude, was chosen for reconstructinglocal annual precipitation due to its highest correlation



Table 5. The statistics for the verification-calibration of each construction are listed below.

Local precipitation reconstruction Periods of calibration – verification1958–2009 1958–1983 1984–2009

Period N Adjusted R2 PRESS RE R2 RE R2 RE R2 RE

1958–1983 26 0.654 0.45 0.672 0.615 0.590 0.564 0.6001984–2009 26 0.545 0.49 0.619 0.615 0.613 0.668 0.6661958–2009 52 0.608 0.41 0.613 0.668 0.677 0.564 0.617

Regional precipitation reconstructions1918–2006 1918–1947 1948–1977 1978–2006

Period N Adjusted R2 PRESS RE R2 RE R2 RE R2 RE R2 RE

1918–1947 30 0.485 0.53 0.520 0.454 0.417 0.534 0.528 0.339 −0.014b1948–1977 30 0.510 0.54 0.540 0.458 0.448 0.501 0.490 0.356 0.1401978–2006 29 0.308 0.51 0.357 0.453 0.372 0.483 0.258 0.542 0.4231918–2006 89 0.447 0.56 0.459 0.474 0.511 0.543 0.534 0.352 0.228

Drought reconstruction of negative δP anomaliesa

1918–2006 1918–1962 1963–2006

Period N Adjusted R2 PRESS RE R2 RE R2 RE R2 RE

1918–1962 16 0.542 0.15 0.603 0.586 0.518 0.669 0.4701963–2006 23 0.681 0.14 0.710 0.556 0.422 0.563 −0.110b1918–2006 39 0.563 0.16 0.586 0.586 0.586 0.602 0.514 0.678 0.624

Explanation of terms: PRESS is a predicted sum of squares statistic that assesses the model’s predictive ability; low numbers are more significant(see text). RE is reduction of error related to the reconstruction and met data’s residuals, and is statistically valid above 0.aOnly the negative anomalies are tested here; the RE of the complete data set’s reconstruction and verification is close to 0.bThe negative REs are the result of 1–5 years of substantial differences between precipitation anomalies and their reconstruction, but thesedifferences are mainly in years when the anomalies are in the 1 to −1 value range.

and response functions with the MSH chronology. Thedata set from the Peristerona, station, located 10 kmNNW of Mitsero, at about 200 m lower altitude, wasused for additional verification of the local reconstructionback to 1918.

The combined monthly precipitation anomalies(1918–2009) from the stations used in the regionalconstruction correlate significantly with at least one ofthe four site chronologies for September of the yearbefore growth through August of the year of growth(Figure 3). The few significant correlations in the monthsbefore and after along with the results of the responsefunction results indicated that the tree rings recordannual rather than sub-annual precipitation fluctuations.This response was also found in a study using tree ringsas an indicator of past droughts in the Aegean Sea region(Sarris et al., 2007).

An examination for any record of temperature in theP. brutia chronologies revealed only a few significantresponses to monthly temperature. Only the highersite chronologies had opposite responses to tempera-ture during the winter and into the beginning of thegrowing season. Temperature will affect the amountof evapotranspiration and thus water availability at thelower elevations, and the initiation of the growing seasonat all elevations. For the P. brutia represented in ourstudy, any effect of temperature on tree-ring growth wasnot consistent over time.

As noted above, Agios Epifanios is the meteorolog-ical station whose annual precipitation data were usedfor the local reconstruction. We assumed that the area

Figure 4. The local precipitation calibration and verification data sets.The local precipitation is the September through August anomaliesfrom the Agios Epifanios station. The time series of the reconstructionsin each half were calculated using the regression equation from the

calibration of the other half. See Table 5 for supporting statistics.

represented by this reconstruction would include at leastthe immediate area around the site and weather sta-tion northeast of the Troodos Mountains, and possiblyextend over most of central Cyprus. The chronology andthe precipitation data were divided into two segments,1958–1983 and 1984–2009, for calibration and verifica-tion (Figure 4, Table 5), and the verification confirmedfor 1918–1957 with the Peristerona data. The chronol-ogy’s common signal explains 61.5% of the variance inthe annual September to August precipitation, which isremarkable for a single site chronology.

The local reconstruction is shown in Figure 5(a); thereconstruction is listed in Table S1 in the supplement. In


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(a)

(b)

(c)

Figure 5. The local and regional September to August annual meteorological precipitation records compared with (a) the local annual precipitationreconstruction in central Cyprus, (b) the regional annual precipitation reconstruction for low-mid latitudes in Cyprus and (c) the regional drought

reconstruction.

addition to the drought years, the significantly wet yearsare well represented in this reconstruction (Figure 6(a))due to the site’s low altitude and aridity. The results andcomparisons with precipitation data from other stationsand other reconstructions indicate that this reconstructionis consistent with the precipitation record across mostof the lower altitude region of the island. The droughtyears are included in the analysis and discussion below.

For the regional reconstruction we included all sitechronologies in order to cover the represented altitudi-nal gradient in the reconstruction. Principal componentswere extracted from the four sites’ chronologies. Thefirst component contains the variation common to allthe chronologies with approximately equal values forthe three chronologies from the higher altitude sites, andslightly less for the MSH chronology. The second com-ponent contains a definite variation along their altitudinaltransect, with MSH at one end and DST at the other. PC1explains 63.9%, and PC2 21.1% of the variance; together85.0% of the variance is explained. The two PCs wereused in regression analyses with the regional precipitationanomalies data to analyse the response functions.

The calibration and verification from the PC analysison the sub-time series and sub-sample groups resulted innearly identical reconstructions. The calibration and ver-ification data statistics are listed in Table 5 and shownin Figure 7, and the reconstruction back to 1830 isillustrated in Figure 5(b). Kienast et al. (1987) found avery local record of climate parameters in tree growthwith regard to both elevation and the individual sites’terrain in the Troodos Mountains. With the combinationof the four chosen site chronologies we have successfullyreconstructed a regional drought record extending intothe higher elevations where temperature can also be alimiting factor in the winter months but not consistentlyover time, as noted above. Figure 6(b) shows the recon-struction’s good representation of drought; the drought

years are listed in Table 6. The two longer chronologiesfrom the trees at the RVA and STV sites in the middle ofthe altitudinal transect were used to extend the droughtassessment back to 1756. The same procedures were usedas in the regional reconstruction but with the two sitechronologies rather than the PCs. Its reconstruction isa record of drought years only (Figures 5(c) and 6(c))from the common signal of the two chronologies. Thevariance explained by the complete time series is con-siderably reduced but there is only a slight decrease invariance explained within the drought years (Figure 6(c),Table 5). These drought years are included in Table 6,and discussed below.

3.4. Seasonal variability in precipitation and its recordin the tree-rings

An 11-year running mean of the seasonal precipitationdata sets over time (Figure 8) shows definite low-frequency variability both between seasons across time.In general, an increase in autumn and winter precipitationhas a positive effect on ring growth due to the amount ofwater available for the coming growth period. A decreasein autumn precipitation is not important when there is asubstantial amount of winter precipitation to offset thatdecrease. An increase or decrease in winter precipitationgenerally has equal influence on ring growth due tothe high amount of that season’s precipitation, but ismost important for the trees on the drier sites at lowerelevations.

For spring, decreasing and low precipitation affectstree growth most at the higher sites due to the importanceof water availability at the onset of the growing season.The effects of an increasing and high precipitation inspring on ring growth are relative to the altitudinalgradient, with MSH the most affected, and DST the least.

Finally, summer precipitation has consistent influ-ence on growth only at the higher altitude sites where



Table 6. List of years of annual, sustained and extreme sustained droughts in the reconstructions (LR = local, RR = regional,DR = drought) and in the meteorological data (LP = local, RP = regional). The bold years and letters are in the clustersof multi-year droughts in 1806–1825, 1915–1934, and 1986–2000. The extreme sustained drought of 1785–1787 is the only

multi-year drought that stands alone.

Years Years

Begin End Reconstruction (NA) Begin End Reconstruction Precipitation

Drought reconstruction only 1902 All1759 DR 1911 LR1765 DR 1915 1917 All1768 DR Regional precipitation begins1782 DR 1925 (RR, LR) RP1785 1787 DR 1927 1928 All RP1794 DR 1932 1933 All RP1806 1808 DR 1934 DR1819 1824 DR 1941 All RP1826 DR 1944 RR, LR1829 DR 1947 DRDrought, regional and local 1951 (DR), RR, LR (RP)1837 All 1953 DR1840 All 1957 DR (RP)1845 RR, LR Local precipitation begins1849 DR 1959 All All1851 DR, RR 1964 All All1854 DR 1966 LR LP1855 RR, LR 1970 RR, LR RP, (LP)1870 RR, LR 1973 All All1873 All 1986 RR, LR RP1875 RR, LR 1990 DR RP1879 RR, LR 1991 All All1881 LR 1994 RP1887 DR, RR 1997 1998 RR, LR All1899 All 2000 RR, LR All

2008 LR LP

precipitation is greater and the growing season is shorterdue to cooler winter temperatures. In contrast, summerprecipitation has some influence on MSH ring widths,but it is effective only in years with a relatively highamount of summer rainfall.

This finding partially indicates why the trees haverecorded an annual record over time. The primary growthlimiting factor for the trees is a combination of allseasons, and the variations in seasonal precipitation aresubstantial.

3.5. The reconstructed drought record

For an assessment of drought pertaining to water scarcity,the frequency and severity of droughts were examinedfor possible patterns and variations in those patterns overtime. We defined drought years as those with normal-ized annual precipitation anomalies lower than −1 stan-dard deviation, sustained droughts have two consecutivedrought years, and extreme sustained drought are sus-tained droughts plus consecutive years with anomaliesless than −0.75 standard deviations (Table 6).

In the meteorological data and its extensions by thereconstructions there are 62 drought years over the250 year represented (Table 6). Most are annual droughts,but there are significant shifts in the frequency andseverity of droughts over time, with distinct clusters of

sustained droughts and extreme sustained droughts in theyears of 1806–1824, 1815–1934 and 1986–2000. Forthese three periods, each covering 20 years or less, abouthalf of the years were drought years. Outside of thoseperiods the frequency is much reduced, with one annualdrought occurring every 5–6 years over time.

4. Discussion

4.1. Current and historical perspectives

The frequency and severity of droughts in the last twodecades of the 20th century plus the 2008 drought(Table 6) have raised serious concerns about waterscarcity and the future of Cyprus. Understandably, theconsistently dry periods, especially at lower elevations,are of considerable importance to the government, anddrought risk and concerns regarding mitigation strategiesare now prominent topics for Cyprus (Tsiourtis, 2008).The precipitation and drought reconstructions are validproxy records of low to mid-latitude inland precipitationdue to the similarity of the local, regional and droughtreconstructions and the highest variance explained by thelocal reconstruction from the low altitude site.

From a historical perspective, several of the single-and-multi-year drought periods in the local and regional


C. GRIGGS et al.

(a)

(b)

(c)

Figure 6. Reconstruction versus. precipitation for the periods repre-sented by the meteorological data. (a) Local reconstruction vs. thelocal Agios Epifanios station data; (b) Regional reconstruction versusthe regional precipitation and (c) The drought reconstruction versusregional precipitation. Note the strong correlations in the drought years

with anomalies of < −1.0 in all figures.

reconstructions (Table 6) correspond well with historicaldata from Cyprus and the northeastern Mediterranean.The 1837 drought year from our reconstruction matchesa historical record of particularly severe crop failurefrom 1836 to 1838. During this time, famine was sosevere that American missionaries to Cyprus reportedlocal inhabitants selling their clothing in exchange forfood, and many left the island for Syria and AsiaMinor (Harris, 2007). The 1881 and 1887 droughtyears from the reconstruction correspond to a decadeduring which British officials of the Cypriot colonialgovernment report low rainfall and poor agriculturalyields (Harris, 2007). The 1887 drought extended beyondCyprus to other neighbouring areas, with widespreaddrought and famine in Anatolia reported in the Ottoman

Figure 7. Calibration and verification of the regional precipitationreconstruction is shown here compared to the meteorological Septem-ber to August precipitation anomalies. The regional reconstruction ineach of the three segments was calculated using the regression equation

from a different segment. See Table 5 for supporting statistics.

archives (Kuniholm, 1990). Other periods of reporteddrought, crop failure and famine in Cyprus and theimmediate surrounding region (1768, 1870–1874, 1901and 1931–1933) (Thirgood, 1987; Harris, 2007) alsocorrespond well with our reconstruction.

4.2. Annual versus extended droughts with possibleteleconnections

Any drought will decrease water availability of a givenyear, but when a drought year occurs between yearsof rainfall close to or above average, its overall effecttends to be related only to that year without muchimpact on the following years. In contrast, the multi-yeardroughts have significant impact on water availabilitydepending on their severity, duration and frequency. Themulti-year droughts in the three relatively short periodsreflect the low precipitation of half the represented yearsand a decreasing amount of available reserves, eitherin groundwater or stored photosynthates (Yaseef et al.,2010). The cause of the multi-year drought periods maybe due to the impact and teleconnections of larger-scale climate forcings which are known to have aninfluence on the weather patterns and climate of theeastern Mediterranean region. They include the NAO(Barnston and Livezey, 1987; Hurrell, 1995) and theEAWR (Krichak and Alpert, 2005a, 2012), also knownas the North-Sea Caspian pattern (Unal et al., 2012).

The effect of the winter NAO and its influence andrelationship with the EAWR on eastern Mediterraneanclimate is well known (Gündüz and Özsoy, 2005). Thevarying circulation patterns caused by the strength ofeach force over the island indicate that a positive NAOinducing a positive EAWR has a negative effect onprecipitation (Krichak and Alpert, 2005a, 2005b; Unalet al., 2012). A negative NAO has minimal impact dueto its weaker state, but the EAWR appears to maintainits inverse relationship with annual precipitation on thelow-frequency scale, at least back to the beginning of itsdata set in 1950. The winter NAO was mainly positivefrom 1902–1934 to 1980–2001 (Jones et al., 1997), butthe reconstructions of the winter NAO farther back in



(a)

(c)

(b)

(d)

Figure 8. The 11-year running averages of seasonal precipitation data from the four stations utilized in this study. (a) represents Septemberthrough November; (b) December to February; (c) March to May and (d) June to August. The Y -axes all have the same scale except for thetop portion of (b). Note the overall increasing trend in autumn (a), and decreasing trend in the winter months (b). Of significance is the slight

rebound in the winter and spring groups since 1995 along with the increase in the autumn (see text for discussion).

time are problematic in the late 1700 s to early 1800 s.While the reconstructed winter NAO of Luterbacheret al. (1999) is negative for ca. 1805–1820, two otherreconstructions give a positive NAO during that period(Cook et al., 1998; Griggs et al., 2006). The similarityof the extended period of drought in the early 1800 s tothose in the early and late 20th century indicated by thetree rings suggests that there was also a strong positivewinter NAO at that time. Those three periods are whenthe sustained droughts occurred.

4.3. An assessment of the last severe drought period

The precipitation and drought reconstructions indicatethat the two periods of extreme and sustained droughtsprior to the late 20th century drought are around 20 yearsin length (1806–1824 and 1915–1934). But can we besure that the last drought ended in 2000?

In the meteorological data of 1917 up to 2008, therewas a slight decrease in annual precipitation despite theconsiderable decrease in winter precipitation (Figures 5and 8). The precipitation of winter and spring, at signif-icant lows in the last two decades of the 20th century,appears to have increased very moderately at the begin-ning of the 21st century (Figure 8). This increase issimilar to the trends in the 1920s and 1930s (Figure 8),suggesting that the last drought period has ended, andthat 2008 is one of the annual droughts that occur every5 years. A continued increase in precipitation for the early21st century is further supported by the overall higheramounts of annual precipitation in Cyprus from 2009 to2011, at 125, 85 and 111% of the average precipitationfor 1961–1990 (Cyprus Meteorological Service, 2013)

and the lack of drought between 2000 and 2008. Thelower amount of winter precipitation in inland Cyprussince the 1970s is still a concern, but it was at approx-imately 70% in the 1990s and has increased to 90% in2001–2011 relative to its average amount in1931–1960.Finally, the end of the positive phase of the NAO at theturn of the century also suggests that the drought periodthat began in 1986 ended in 2000.

5. Conclusions

Annual precipitation and a 250-year drought record werereconstructed from four Pinus brutia tree-ring chronolo-gies from four sites at varying altitudes in the TroodosMountain Massif in Cyprus. A robust local precipita-tion reconstruction from AD 1830 to 2008 was producedfor the rain-shadow area on the northeastern side of theMassif which is relevant to one of the main populationand settlement areas of Cyprus. The regional precipi-tation from the four chronologies added the variabilitydue to altitude and the influence of the Troodos Moun-tains, but its drought record does not substantially differfrom the local precipitation reconstruction. The droughtreconstruction was extended back to 1756 using the twolongest chronologies from sites between the low andhigh-altitude sites, and it represents the first longer termannual precipitation and drought reconstruction from thelow to mid-elevations of Cyprus. The reconstructions alsodemonstrate the potential of Pinus brutia chronologies foraccurate reconstruction of annual resolution climate his-tories and climate variability on local and regional scales.


C. GRIGGS et al.

The drought reconstruction shows that annual droughtsoccur about once every 5 years except in periods ofsustained droughts. The sustained drought periods, ofaround 20 years in length, occur every 70–100 years,with the two 20th century periods within extendedpositive phases of the winter NAO. With the lastextended drought period at the end of the 20th century,it is most likely that similar conditions will not occuragain until the last half of the 21st century. However,two alternative scenarios are possible. One scenario isthat the recent drought period may continue as suggestedby the severe drought of 2008 despite the indicationsto the contrary discussed above. This could happendue to the unprecedented changes in climate and theeffects of anthropogenic influence in the 20th century.The second possible scenario, depending on the strengthof the relationship of the winter NAO forcing to themulti-drought periods, is that a sustained positivewinter NAO may occur sooner than is indicated by itsoccurrence in the last 200 years. In all scenarios thedrought reconstruction presented here provides valuableinsight for prediction and drought mitigation strategies.The precipitation amounts and drought frequency in theyears following 2011 will add to the probability of thisforecast.

Our future dendroclimatological research will focuson further exploration of long-term teleconnections toaccount for differing relationships between the primarygrowth factors in Cyprus across time, particularly in thelate 20th century. In addition we will target other longerlived tree species ubiquitous to the Troodos Massifwhich may provide longer time series and a means forexamination of interspecies variation. Work is currentlyunderway on reconstructions from Pinus nigra (Arn.)and Cedrus libani (A.Rich.) subsp. brevifolia (Hook.f.)from the higher altitude Chionistra and Cedar Valleyareas of the Troodos.

Acknowledgements

The authors would like to thank the Director and offi-cials of the Cypriot Department of Forests, particularlyAndreas Christou, Alex Christodoulou and NathanielAndreou, for access to the forests, resources and assis-tance, and the Forestry officers at the Panagia, Platanosand Stavros tis Psokas stations for their help and hospital-ity. Fieldwork in 2004–2005 was supported by a NSERCgrant; fieldwork and laboratory work 2006-present wassupported by the Malcolm Hewitt Wiener Foundation andthe College of Arts & Sciences, Cornell University. Wewould also like to thank Tomasz Wazny for his field andlab assistance; Jennifer Watkins, Rachel Kulick, Seth But-ton, Eilis Monahan, Sarah Harris, Sara Rich and SarahStewart for field collection and Kayla Altland, JessicaHerlich, Ryan Hunter and John Knecht for assistance withlaboratory analysis. We thank Peter Brewer for creatingthe map (Figure 1). The authors have no conflict of inter-est to declare for this publication.

Supporting Information

The following supporting information is available as partof the online article:Table S1: Precipitation and drought reconstructions from:Griggs et al ; A 250-year annual precipitation reconstruc-tion and drought assessment for Cyprus from Pinus brutia(Ten.) tree-rings.

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