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Climate change of the last 2000 years inferred from boreholetemperatures data from Hungary

L Bodri P Dove nyi Research Group on Geophysics and Environmental Physics Hungary Academy Science co Geophysics Department Eo uml tvo s University

Pa zma ny se ta ny 1c Budapest 1117 Hungary

Received 15 May 2003 accepted 14 October 2003

Abstract

Ground surface temperature (GST) history reflecting past climate conditions in Hungary was evaluated by analysing theexcursions left on the present-day temperaturendashdepth distribution measured by precise temperature logging in 20 boreholesThese data were used to assess climatic changes over the last two millennia We inverted the temperaturendash depth data using thealgorithm by Bodri and Cermak [Global Planet Change 11 (1995) 111] Four main episodes can be distinguished a warm period around 0 AD extended cold conditions in the 6ndash16th centuries a general warming culminated near 1850 and thecooling since then The verification of the GST assessment was accomplished by independent data from historical sources andthe GST reconstructions in surrounding Slovakia and Slovenia The long cold conditions in the Middle Ages and the absence of

the Little Climatic Optimum seem to be generic feature of the climate in Hungary In their more recent parts the obtained GSThistories are consistent with the meteorological records in the areaD 2004 Elsevier BV All rights reserved

Keywords Borehole logging Underground temperature Climate reconstruction Hungary

1 Introduction

The short-term (1ndash 1000 years) temperature changesare generally investigated with the help of the mete-

orological surface air temperature (SAT) records anddocumentaryarchaeological sources Because bothsources have their individual limits (eg shortnessof the existing SAT time series and the non-uniformspacendashtime distribution of the documentary evidenceof climatic change and their indirect character) the

use of independent data to test and complete the past climate picture is indispensable The lsquolsquogeothermalrsquorsquodata represent one of the additional sources of infor-mation about the Earthrsquos changing surface tempera-

ture Due to the low thermal diffusivity crustal rockshave a long thermal memory for temperature changeson the Earthrsquos surface The significance of the under-ground temperatures for the climate reconstructionwas recognised almost as soon as the temperaturendash depth measurements were performed in boreholes(Lane 1923) However systematic attempts of theground surface temperature (GST) reconstructions began only recently In the last two decades numer-ous papers appeared reporting that temperaturendashdepthrecords in drillholes may contain a certain climatic

0921-8181$ - see front matter D 2004 Elsevier BV All rights reserveddoi101016jgloplacha200310001

Corresponding author Tel +361-381-2191 fax +361-381-2192

E-mail address bodripangeaeltehu (L Bodri)

wwwelseviercomlocategloplachaGlobal and Planetary Change 41 (2004) 121ndash133



signa l which can be extracted by inverse methods(eg Cermak 1971 Shen and Beck 1992 Beck et al 1992 Shen et al 1992 Bodri and Cermak 1995

1997 Huang and Pollack 1997 Rajver et al 1998 )As geothermal borehole measurements are generallyavailable from many regions on all continents theymay represent a useful tool for climatic reconstruc-tions in areas less covered by traditional climaticinvestigations

In the present study GST history is assessed from20 Hungarian boreholes This area is poorly covered by the traditional climatological data thus the geo-thermal results could provide an important supple-ment to the sparse evidence on the climate change inHungary The study is completed by a comparison of the obtained results with the GST reconstructionsfrom the neighbouring Slovakia and Slovenia histor-ical sources and the long-term meteorological meanannual series

2 Data

The first measurements of the outflowing water temperature in Hungary were carried out by Zsig-mondy V between 1866 and 1877 in the notable

drillings Harkany Margitsziget and Varosliget Thefirst borehole temperature logging in Hungary was performed by Papp K in 1919 in the boreholeVarosliget (Budapest) and the first measurementsfor heat flow density d eterminations began in the1950s (Boldisza r 1956) The present day catalogueof the temperature data in Hungary contains over 4000 temperature logs collected by Dove nyi et al(1983) Most of the borehole temperaturendashdepth pro-files were measured in the last decades of the 20thcentury at various geological settings by several

institutions and logging centres with different techni-ques and thus varying significantly in quality Major-ity of these logs were measured for the hydrologicalresources andor oil prospecting and are not suitablefor climate reconstructions Often the problem is that after drilling is completed the boreholes did not haveenough time to achieve stable thermal conditions For the classification of the existing temperature logsthere were worked out a rather rigorous data rankingcriteria (for example temperatures measured under steady state conditions temperatures measured during

drill stem tests both in water and petroleum explora-tion wells etc) and applied to Hungarian data set (Dove nyi and Horva th 1988 Horva th and Dove nyi

1991) Measurements under thermal equilibrium (thetime interval between drilling and temperature meas-urements achieved 1ndash2 years) were performed in only61 of all the boreholes However a significant part of these temperaturendashdepth profiles contains only two tofour measured points This amount is far not enoughfor the recovering of the detailed GST history Thusonly 20 from a heap of available profiles are suitablefor climate reconstructions The accura cy of the meas-urements is estimated to be 10ndash15 (Dove nyi et al1983 Horva th and Dove nyi 1991) Chosen boreh olesare regularly distributed throughout the country (Fig1) Thus results of climatic reconstructions can pro-vide also information about regional distribution of climatic changes

The selected boreholes were drilled in generallysedimentary strata All they are situated out of themain areas of advective heat disturbance in HungaryIn these areas flow of water is driven by the hydraulichead differences generally associated with topograph-ic changes andor with the Mesozoic carbonates in thePannonian basin These rocks are characterized byhigh secondary permeability occurrin g because of

intensive fracturing and karstification (Erde ly 1985) In the selected borehole sites a regional water flowsystem is related to the expellation of formation water from the pore spaces due to progressive burial andcompaction of rocks (Horva th and Dove nyi 1991) Geothermal data and model calculations have shownthat this flow is normally very slow and perturbsinsignificantly the conductive temperature field (Steg-ena 1982 Alfoldi et al 1985) Other main non-climatic causes of the nonlinearities in temperaturendash depth profiles such as topography urban heat sub-

surface heat production are also negligible As wasmentioned above boreholes were drilled in generallysedimentary so-called Upper Pannonian strata Thisformation covers the most part of the country andrepresents the Pontianndash Pliocene basin fill whichconsists of a delta-plain sequence with frequent alter-nation of sands sandstones siltstones and clayeyndash marly layers (Dove nyi et al 2002) Information onthe thermal conductivity exists for the 12 of 20 bore-holes The 20 to 50 core samples were available fromeach borehole ( Dove nyi et al 1983 Table 3) In

L Bodri P Douml ve nyi Global and Planetary Change 41 (2004) 121ndash133122



boreholes without thermal conductivity measure-ments the lithology of the penetrated depth intervals

was known in detail because of existing continuouswell-logs An analysis of the thermal conductivitydata measured on different rock samples in the Pan-nonian basin fill led to a good knowledge of thegeneral trend of thermal conductivity change withdepth for different lithologies (Dove nyi and Horva th1988) This gives a possibility to make thermalconductivity estimates for boreholes where the lithol-ogy of Neogene strata is known Because thermalconductivity values exhibited only small variationsabout the mean and most importantly showed no

systematic variation as a function of depth thermalconductivities were assigned their mean values(Tables 1 and 2)

Reliable estimates of the GST history could be performed for 10 boreholes sampled with sufficient dense rate Temperature logs and technical informa-tion of these boreholes are presented in Fig 2 andTable 1 The rest 10 borehole temperature logscontained less than 10 measured points and themeasurements began below 100-m depth thus theydo not contain information about climatic events at

least of the last 100ndash200 years (Bodri and Cermak1995) These boreholes were used for a simpler

climatic reconstruc tion as applied for the first time by Cermak (1971) Climate change is represented as a

Table 1Summary of the geothermal data for 10 Hungarian boreholes that were suitable for GST inversion

n Borehole Depthinterval (m)

N Go (Kkm) K (Wm K)

1 Artand-2 10 ndash 1010 11 375 F 55 202 Fuzesgyarmat-2 10ndash1260 14 628 F 12 273 Jaszbereny-1 10 ndash 1225 14 493 F 09 274 Kurd-3 50 ndash 450 10 765 F 14 205 Mihaly-37 60 ndash1570 24 516 F 08 276 Pusztafoldvar-6 10ndash1250 14 712 F 34 207 Recsk-8 50 ndash 880 10 306 F 08 278 Recsk-15 35 ndash 825 10 309 F 06 279 Szalatnak-4 50 ndash700 11 508 F 17 3010 Szirak-2 50 ndash1585 25 382 F 08 28

Column lsquolsquoBoreholersquorsquo indicates the site and the number of boreholeaccording the catalogue by Dove nyi et al (1983) N is the number of measured points G o is the temperature gradient and K is the thermalconductivity Column lsquolsquoDepth intervalrsquorsquo represents the interval of depths where the temperature measurements were performed

Fig 1 The locations of the boreholes studied for climate change reconstruction in Hungary

L Bodri P Do ve nyi Global and Planetary Change 41 (2004) 121ndash133 123



simple instantaneous temperature change of D T fromthe previous T o to T temperature ( D T = T Agrave T o ) at thetime t In this case temperature variation T takes the

simple form

T eth z t THORN frac14 T o thorn G o z thorn D Terfcz

2 ffiffiffiffiffiffiffiffiffiffiffiffiffik etht Agrave t THORNp

where z is depth t is time k is the thermal diffusivityT o and G o are the parameters of the steady-statetemperature field (see below) Negative D T meanscooling in comparison with the previous temperatureand D T gt0 implies warming Unknown parameters of climatic change D T and t can be estimated by the

least-squares inversion technique Technical informa-tion of these 10 boreholes and estimated parameters of the climate change are presented in Table 2 Thermal

diffusivity was estimated from the measured conduc-tivity and assumed standard value of the volumetricspecific heat of 25 MJm 3 K

3 Inversion technique

Temperature changes at the Earthrsquos surface diffuseinto the subsurface by heat conduction and manifest themselves as a perturbations to the otherwise quasi-steady state background temperature field Depth and

Fig 2 The Hungarian temperatu rendashdept h profiles used for the GST reconstructions Symbols show the individual temperature measurements1ndash10 identification numbers in Table 1 Inset shows the upper parts of the temperature logs




time of the climatic change are linked nonlinearly bythermal diffusivity For the diffusivity of 10

Agrave 6 m2 stemperature changes that occurred 100 years ago have penetrated to only 80 m whereas changes that oc-curred 1000 years ago have penetrated to 250ndash300 mBoreholes of several hundred meters depth maytherefore contain a response of the Earth to the surfaceground temperature changes over the last 1ndash2 millen-nia Because of the low thermal diffusivity of crustalrocks the high frequency components are diffused out with time therefore only signals of long wavelength

temperature variations at the Earthrsquos surface are pre-served GST history can be recovered from the sub-surface temperature ndash depth profiles by inversetechniques The inverse method used in present studyis described by Bodri and Cermak (1995 1997) Thismethod was tested on numerous synthetic and mea-sured temperature logs It is based on the theory of heat conduction in a layered laterally homogeneousmedium The thermal properties of the medium areregarded as known quantities their uncertainties arenot taken into account which may be rather severe

restriction in case of a complex stratigraphy andinadequate thermal conductivity coverage (Shen et al 1992) In order to reconstruct past climatechanges we used the generalised least-squares inver-sion technique (Bodri and Cermak 1995) whichminimises both the sum of the squares of deviationsof the measured record from the theoretical model andthe sum of the squares of the estimated parametersThe surface temperature history is approximated by aseries of individual intervals of constant temperatureThe mean values of temperature in the individual time

intervals are unknown parameters Discretization of time depends on many site-specific factors andshould be established for each borehole individually by means of the resolution matrix (for details seeBodri and Cermak 1995 ) When representing theresults graphically we ascribe the obtained tempera-ture values to the middle points of the correspondingtime intervals and then draw a smoothed curvethrough these points Temporal resolution of the borehole GST reconstructions decreases into the pastIt depends on the shape of the surface temperature

history and is also a complex function of many borehole specific parameters such as accuracy andvertical spacing of the temperature measurementsdistribution of thermal conductivity measurementsetc The experiments with synthetically generatedtemperature logs randomly perturbed by noise withGaussian distribution can reveal the upper limits of the resolution According to Bodri and Cermak (1995) the reliability of the determination of theGST change is about 10ndash15 for a change whichoccurred 50 years ago Changes which occurred 200

years ago can only be resolved by a 50-year intervalof the same reliability and by a 200-year interval for achange which occurred 800 years ago (see alsonumerical experiments by Beck et al 1992 ) Recon-structed temperature variations become damped to-wards the past due to progressively increasingsmoothing character of the inversion method Warm-ing or cooling signals can be amplified or attenuatedthrough the choice of the singular cut-off value whichrestricts the resolution but improves the stability of thesolution The optimal choice of the cut-off value does

Table 2Summary of the geothermal data for 10 Hungarian boreholes used for an instantaneous temperature change climatic reconstruction

Borehole Depthinterval (m)

N Go (Kkm) K (Wm K)

D T (K) t (years BP)

Kovagotottos-2154 100 ndash 810 8 401 F 06 31 Agrave 22 F 14 450 F 130Kovagotottos-3175 100 ndash 890 8 337 F 09 31 Agrave 25 F 11 670 F 190Kovagotottos-4242 100 ndash 780 8 224 F 12 31 Agrave 11 F 06 530 F 90Kovagotottos-4294 120 ndash 920 9 395 F 13 31 Agrave 10 F 05 550 F 110Kovagotottos-4508 120 ndash 720 7 403 F 13 31 Agrave 29 F 18 370 F 140Kovagotottos-5065 100 ndash 800 8 405 F 15 31 Agrave 30 F 17 500 F 130Val-3 25 ndash 900 7 454 F 19 28 Agrave 12 F 04 600 F 150 Nagylengyel-60 50 ndash 2025 8 489F 18 185 16 F 04 2130 F 490 Nagylengyel-75 500 ndash 2150 9 460F 15 185 21 F 19 2590 F 780 Nagylengyel-100 500 ndash 2300 7 497F 27 185 12 F 10 2850 F 580D T is the temperature change at the time t Other columns are the same as in Table 1

L Bodri P Douml ve nyi Global and Planetary Change 41 (2004) 121ndash133 125



a deal between the variance of the estimated GST andthe resolution It should be mentioned however that the warming trend cannot be transformed into a cool-

ing trend or vice versa through the choice of the cut-off value Strategy for o ptimal choice of the cut-off values is described by Bodri and Cermak (1995) Numerous trial runs with synthetic examples haveshown that the reconstructed GSTs agree almost perfectly with the past conditions in the recent 200ndash 300 years while the amplitude of climatic changesthat occurred 800ndash1000 years before present may besmoothed down to approx 50 of its initial value

The bulk of the observed temperatures represents aquasi-steady state geothermal field For a homoge-neous isotropic rock strata having no internal heat sources the steady-state temperature T S increaseslinearly with depth as T S = T o + G o z where z is depthT o and G o are the quasi-steady-state ground surfacetemperature and temperature gradient respectively Toinvestigate temperature perturbations in the measured profiles that might have been caused by climatechange we used the reduced temperature T R defined

as T R ( z ) = T M ( z ) Agrave T S ( z ) which represents transient departure from the steady-state conditions and T M isthe measured temperature The parameters of the

steady-state temperature field presented in Tables 1and 2 were calculated from the lowermost parts of themeasured temperature logs by the standard linear regression technique The transient component isassumed to be caused by time variations of the groundsurface temperature

4 GST reconstruction in Hungary

Ten temperature logs presented in Table 1 wereinverted in dividu ally the obtained GST histories areshown in Fig 3 Because of significant depth of themeasured temperature logs the GST histories could be reconstructed for the last two millennia Howeverthe relatively coarse sampling (depth step was as arule 50ndash 100 m in comparison with the usual ingeothermal logging 5ndash10 m or even finer samplinginterval) permitted us to resolve only two to three

Fig 3 Reconstructed GST histories for 10 boreholes presented in Table 1 Thick line represents mean value of eight boreholes except of theRecsk-8 and Recsk-15




main climatic episodes that had the greatest impact onthe temperature log in a given environment It should be mentioned however that the course sampling has

impact generally on the re cent segments of the GSThistory As was shown by Bodri and Cermak (1997) for 1ndash2-km-deep boreholes with finer sampling of 5ndash 10 m generally four to six climatic events could beresolved within the last 2000 years time intervalHowever two to three of the resolved events wereconcentrated in the interval between approx 1800 ADand the present

The range of the GST changes obtained for differ-ent boreholes is very similar Temperature oscillationsmay vary within the range of 18ndash 31 K with themean value of 222 F 114 K The coincidence of theshape of the obtained GST histories is rather goodexcept of the two closely spaced boreholes at Recsk site which implies that all borehole sites were sub- jected to the same or very similar climate changesand that noise is probably introduced by the temper-ature measurements and the errors caused by theinsufficient representation of the conductivity Be-cause the temperature logging was performed morethan 20 years ago it is now impossible to examine theconditions existing in the close vicinity of the Recsk boreholes However since both holes at Recsk gave

very coherent GST histories their inconsistency with

other GST curves is not simply an artefact of inversionand probably reflects definite local conditions Thedifferences between GST histories from the boreholes

Recsk and closely spaced borehole Szirak could beexplained by the influence of the mountain climateThe two boreholes Recsk are situated within theCarpathian Mts at the northern border of the Matramountain range belonging to Carpathian system Thesite of borehole Szirak belongs to the southern low-land of other mountain range of Carpathians theCserhat Mts This conclusion can be confirmed bythe comparison of the climatic trends reconstructedfrom the Recsk temperaturendashdepth profiles with theGST r econstructions for the neighbouring boreholesFig 4 shows the GST histories calculated for twoSlovakian boreholes Gondovo (4828 j N 1866j E)and Zlatno (4841 j N 1878j E) located at some100ndash120-km distance NW of Recsk at sites also belongin g to the different ranges of the Carpathiansystem (Bodri and Cermak 1999) These GST histo-ries appear to be generally coherent with the GSTtrends obtained for the Recsk boreholes the range of temperature excursions is near 3 K The main epi-sodes are a cooling between 1800 and 1900 AD andgeneral warming since then

The general course of the climatic excursions in

Hungary can be traced on the curve representing the

Fig 4 Temperature logs for boreholes Gondovo (PKS-1) and Zlatno (R-9) and the corresponding reconstructed GST histories compared withthe GST reconstructions from the boreholes at Recsk




arithmetic mean of the eight GST histories (Fig 3) The results revealed warmer conditions before 500AD followed by a long period of cooling from the 9th

to the 16th centuries and culminated between 1300ndash 1500 AD pronounced warming with the maximum inthe second half of the 19th century and cooling sincethen The range of climatic excursions achieved F 2K The warming period approx 2000 years ago is alsoconfirmed by the values of D T estimated in three boreholes at Nagylengyel (Table 2) Significant depthof the measured temperature logs at Nagylengyel sitethat exceeded 2 km permitted to recognise theseremote warming events All boreholes revealed rather synchronic warming occurred 2000ndash3000 years BPthe end of which is visible also at the GST histories inFig 3 This warm period can be associated with theso-called secondary Optimum which is defined incomparison with the Atlantic period (6000ndash 3000BC) represent ing the warm est postglacial timesAccording to Lamb (1977) there was a gradualrecovery of warmth in Europe over approx 1000years after 600 BC particularly after 100 BC leadingto a period of warmth Subsequent cooling is alsoconfirmed by the results of the estimations of the stepchange in climate for boreholes Kovagotottos and Val(Table 2) which showed 1ndash 3 K cooling 400ndash 700

years BP thus in the years 1300ndash1600 AD

5 Discussion and conclusions

The instrumental temperature records are typicallyavailable for no more than the past 150 years There-fore reconstruction of pre-industrial climate relies principally on traditional climate proxy records and borehole temperature inversion Generally four mainclimatic episodes for the period since the Early

Middle Ages to the end of the 19th century could be recognised in Europe The warmer times culminat-ing near 300 ndash400 AD are documented eg bydendroclimatological records (maximum density of late wood in the tree rings radiocarbon dates of fossiltrees found above the present tree line) from Switzer-land (Rothlisberger 1976 Renner 1982) The cold period with its climax between the 8th and 10thcenturies is documented by the general paleoclimatictrend in Europe reconstructed by Williams and Wigley(1983) by using a variety of proxy sources This

period was also revealed in the most reliable globaltemperature reconstruction by Huang and Pollack (1997) who examined a large archive of continental

heat flow measurements for evidence of late Quater-nary temperature variations Data characterize both periods as quite durable (eg fossil trees are foundabove the present tree line from the times 100 to 500AD) The following warm period sometimes calledlsquolsquoLittle Climatic Optimumrsquorsquo is re ported by Lamb(1977) Flohn and Fantechi (1984) as well as in thereconstructions by Huang and Pollack (1997) withclimax occurring between years 1150 and 1300 ADAn analysis by Crowley (2000) indicated howeverthat this Optimum was less distinct and more moder-ate in amplitude as compared to the mid-20th-centurywarm period The Medieval temperature peaks werenot synchronous in different records The late 16thand 17th centuries extreme condition called lsquolsquoLittleIce Agersquorsquo is th e period of cold climate Accordin g toLamb (1977) and Flohn and Fantechi (1984) themaximum development of the Little Ice Age alsoagrees with the historical maximum advance of theAlpine glaciers (1600ndash1660 AD) or with the maxi-mum tree-ring de nsity in Switzerland and Austria(1575ndash1650 AD Williams and Wigley 1983 ) How-ever according to studies by Bradley (1994) there

exist significant differences in details of principalevents appearing in the reconstructions of temperaturehistories indicating spatialtemporal inhomogeneities

The first of the foregoing periods is clearly visiblein our GST reconstructions and is supported also bythe climate change parameters estimated for the Nagylengyel site However the further course of climatic history in Hungary seems to represent asingle durable cold period which has continued from6ndash7th to 15ndash16th centuries This paleoclimatic trendis confirmed by the results of the GST reconstructions

by (Rajver et al (1998 fig 7a) for the almost 2000-m-deep temperature profile of the borehole Ljutomer (Lj-1) Slovenia situated close to the SW Hungarian border (4651 j N 1619 j E) Inversion was performedwith the functional space inversion method by Shenand Beck (1992) Significant depth of borehole per-mitted to reconstruct GST course for the time far before 1000 AD Results (Fig 7a curve depicted witha priori sd 01ndash10 WmK 002ndash02 K) have shownthat the change from the previous warm to the coldconditions occurred at the Ljutomer site after approx




500 AD and the cold conditions prevailed up to 14ndash 15th centuries with the general return to warm con-ditions after that time The cold conditions dispersed

over approx 1000 years seem to be a generic featureof the climate in the area under investigationWhile there is no doubt that the Little Ice Age and

the subsequent warming were probably global inextent the scope of the warming in Med ieval timesstill represents the question under debate (Mann andBradley 1999 Bradley et al 2001 Broecker 2001) Time series of paleotempe ratures reconstructed byMann and Bradley (1999) with the use of various proxy indices have shown that even conditions of the11ndash12th centuries were warmer in comparison withthe subsequent cooling they were far not so warm asthe post-industrial warming On the Northern Hemi-sphere scale these authors interpret the period around800ndash1200 AD as the part of the long-term coolingtrend prior to the industrialisation According to theseauthors the Medieval warmth appears to be mainlyrestricted to areas neighbouring and in the NorthAtlantic which may hint the impact of the century-scale changes in the North Atlantic Oscillation activityon the climate variability

The existing long-term paleoclimate reconstruc-tions in the area under investigation that could help

to verify our GST reconstruction are almost entirely based on the written historical sources In comparisonwith the western European countries where writtendocuments describing climate meteorological eventsandor natural disasters can be found everywhere (egin Italy vast amount of data exists back over the last 2500 years Pfister et al 1999 ) the Hungarian database is more modest All available historical sourcesare included in the compilation by Rethly (19621970) Hungarian data are also stored in the EURO-CLIMHIST database (Pfister et al 1999) Table 3

summarises the number of existing references onclimatic conditions in Hungary In the row lsquolsquototalrsquorsquoof this table we took into account only those notesthat directly refer to climate conditions (eg coldwarm raining droughts etc) Only those notes werecalculated in the rows lsquolsquocoldrsquorsquo and lsquolsquowarmrsquorsquo that aredirectly connected with temperatures and embracerelatively long periods (eg the years 104344-lsquolsquoThewinter was so severe in Hungary that the cattle hadfrozen to death in the cowshedsrsquorsquo the years 127576mdash lsquolsquoVery severe long and snowy winterrsquorsquo) The natural

disasters such as famine epidemics etc that in principle also can contain information about climaticconditions were not taken into account because of

their rather subjective character and the difficultiesarising in the way to extract exact climatic informationfrom such notes Data on harvests were taken intoaccount only if it was mentioned together with theclimatic conditions (eg the year 1275mdashlsquolsquoSummer was so cold that neither cereals nor fruit and grapedid not grow ripersquorsquo) Specific feature of Hungariandata is that in the most of the documents climaticevents were noted in conjunction with the militarycampaigns like eg famous chronicle by Istva acutenfiMiklo s (Hungarian statesman and historian 1535ndash 1615) and in the diary by Suleiman the Magnificent (Ottoman Sultan 1520 ndash1566) eg the winter of 152829mdashlsquolsquo Suleiman Turkish Emperor came near to occupy Vienna and only extremely cold winter drove his army awayrsquorsquo The numbers in the rowslsquolsquocoldrsquorsquo and lsquolsquowarmrsquorsquo in Table 3 can help to estimatethe proportion of cold against warm periods in givencentury and thus hint to its preference climatic statewhile the row lsquolsquototalrsquorsquo illustrates the part of the coldand warm notes in the total volume of the existingsources

As seen in Table 3 only a few data exists from

each century between 0 and 1000 AD (eg only threenotes from the 10th century) The number of climaticnotes in the documents began to increase only from

Table 3Summary of historical notes of climatic character in Hungary (theexplanations of the terms lsquolsquoTotalrsquorsquo lsquolsquoColdrsquorsquo and lsquolsquoWarmrsquorsquo are givenin the text)

Century Total Cold Warm

II 4 2 1III ndash ndash ndash IV 3 ndash ndash V 3 2 ndash VI 1 1 ndash VII 2 1 ndash VIII 1 ndash 1IX ndash ndash ndash X 3 1 ndash XI 24 13 3XII 14 4 4XIII 44 16 12XIV 26 8 6XV 160 45 51XVI 258 53 68




the beginning of the last millennium (eg already 24notes in the 11th century) However significant amount of data exists only since approx the 15th

century Since 1540ndash1550 AD a few notes can befound for each year The notes on the temperatureconditions generally form 50ndash 70 of all climaticdocumentary sources and significant part of themrefers to exceptionally extreme conditions like citedabove This hints to the recurrent occurrence of extreme conditions before the 16th century in comparison with the unimportant periods that did not deserve to be mentioned in the documents Thelsquolsquocoldrsquorsquo notes prevail above the lsquolsquowarmrsquorsquo entries upto the 14th century and even in the 15ndash16th centu-ries their amount was not significantly behind thelsquolsquowarmrsquorsquo notes Provisional returns of cold conditionshad strong eco nomic and social im pact in Hungary in16th century Landsteiner (1999) describes the wine production crisis in Lower Austria and Western Hun-gary in the late 16th century caused by the oftenoccurre nce of cold winters and frosts late in springData in Table 3 generally confirm the long duration of the cold climate in Hungary and return to warmconditions in the 15ndash16th centuries revealed by our GST reconstructions

Detailed reconstruction of the temperature trends in

Hungary from the 16th century to the present was performed by Racz (1999) who combined historicalclimate information from the various documentarysources These data have been calibrated and verifiedwith the existing SAT instrumental records Resultingclimatic temperatures on the yearly scale of averagingshow moderately cool conditions from the early 16thcentury to the late 18th century The weather in thefirst half of the 19th century turned somewhat milderWhile the mean temperature in the 16ndash18th centuriesslightly oscillated around the mean of 105 j C the

prevailing temperatures for the 19th century wereclose to 11ndash115 j C General warming began in theearly 20th century

The course of the last 500-year climatic history inHungary is to the some degree confirmed also by theGST reconstructions by Rajver et al (1998) for a suiteof boreholes from the north-eastern part of Slovenia(455ndash467 j N 146ndash162 j E) As for the Lj-1 bore-hole inversion was performed by the functional spaceinversion method and embraced period from 1500 ADto the present Results by Rajver et al (1998) revealed

cold conditions prevailing before 1700ndash1800 AD andsubsequent warming with the maxima occurred for different boreholes between the years 1850 and 1975

The GST histories from five of the nine investigated boreholes have shown also recent cooling occurred inthe last decades of the 20th century However theseGST inversions should be used with the some caution because signal in the T ndash z data of some of thementioned boreholes could contain a possible noiseandor be corrupted as a result of larger contrast inthermal conductivity which probably was not com- pletely compensated in the inversion

The times since the beginning of the 16th centuryrepresent the rapid recovery from the pr evious coldconditions to the warmer climate (Fig 3) This warm-ing culminated near 1850 AD in our GST historiesand then has changed by the subsequent coolingHowever this cold period was shorter and not as coldas the previous Little Ice Age The warm episodearound 1850 AD and the subsequent cooling are alsovisible at the meteorological surface air temperature(SAT) r ecord f rom Budapest (data exist since the year 1780 Fig 5) and at the SAT anomalies recordaver aged over the grid box 45ndash50 j N 15ndash20 j E (data by Jones et al 1999 see also wwwcruueaacuk Fig 6) This record begins at the year 1856 and

represents (constructed at the Climatic Research UnitUnivof East Anglia Norwich UK) temperatureanomalies calculated as the deviations from 1961 to1990 base period at the 5 Acirc 5 j grid box basis Bothrecords contain warming episodes around 1800ndash1850and the cooling culminated near 1900 AD Whenexamining SAT records Hansen and Lebedeff (1987) recognised the period between 1940 and1970 as a cooling by 03ndash05 K for whole CentralEurope According to Ghil and Vautard (1991) thewhole Northern Hemisphere was experienced a tem-

perature decrease between 1950 and the mid-1970sThus the variations observed in the reconstructedGST histories since 19th century to the present arein good agreement with the meteorological recordsThe absence of the more recent details than thosedated back to the 1950ndash1970 in the inverted GSTscan be explained by the fact that the most of thetemperature logs begin below 40 ndash60-m depth Theunderground response to a 5ndash10-year-long climatecycle of about 1 K could not penetrate deeper than50ndash70 m (Bodri and Cermak 1995)




Fig 6 Meteorological monthly temperature anomalies averaged over the grid box 45ndash50 j N 15ndash20 j E Thick line represents their 10-year running mean

Fig 5 Annual mean temperatures at the Budapest (KMI) station and their 10-year running mean (data from the Year Books of the CentralInstitute of Meteorology Part 3 Meteorological Service of Hungary Budapest)




Acknowledgements

We are grateful to the Climatic Research Unit

University of East Anglia Norwich UK for thegridded temperature dat a provided from their web siteat wwwcruueaacuk All helpful and valuablemanuscript comments of Drs V Cermak D RajverM Verdoya and an anonymous reviewer are greatlyacknowledged

References

Alfoldi L Ga lfi J Liebe P 1985 Heat flow anomalies caused by water circulation J Geodyn 4 199ndash217

Beck AE Shen PY Beltrami H Mareschal J-C SafandaJ Sebagenzi MN Vasseur G Wang K 1992 A comparison of five different analyses in the interpretation of five borehole temperature data sets Glob Planet Change 98101ndash112

Bodri L Cermak V 1995 Climate change of the last millenniuminferred from borehole temperatures results from the CzechRepublicmdashPart I Glob Planet Change 11 111ndash125

Bodri L Cermak V 1997 Climate change of the last two mil-lennia inferred from borehole temperatures results from theCzech RepublicmdashPart II Glob Planet Change 14 163ndash173

Bodri L Cermak V 1999 Climate change of the last millenniuminferred from borehole temperatures regional patterns of cli-

matic changes in the Czech RepublicmdashPart III Glob PlanetChange 21 225 ndash235Boldisza r T 1956 Terrestrial heat flow in Hungary Geofis Pura

Appl 34 66ndash70Bradley RS 1994 Reconstruction of climate from AD 1000

to the present In Speranza A Tibaldi S Fantechi R(Eds) Global Change Proceed 1st Demetra Meeting ItalyOct 1991 European Commission Brussels pp 123ndash 137EUR15158EN

Bradley RS Briffa KR Rowley TJ Hughes MK JonesME Mann ME 2001 The scope of Medieval warmingScience 292 2011ndash2012

Broecker WS 2001 Was the medieval warm period globalScience 291 1497ndash1499

Cermak V 1971 Underground temperature and inferred climatictemperatures in the past millennium Palaeogeogr Palaeoclima-tol Palaeoecol 10 1ndash19

Crowley TJ 2000 Causes of climate change over the past 1000years Science 289 270ndash277

Dove nyi P Horva th F 1988 A review of temperature thermalconductivity and heat flow data for the Pannonian basin InRoyden LH Horvaacuteth F (Eds) The Pannonian Basin A Studyin Basin Evolution Mem-Am Assoc Pet Geol vol 45 pp 195ndash233

Dove nyi P Horvaacuteth F Liebe P Gaacutelfi J Erki I 1983 Geo-thermal conditions in Hungary Geophys Trans 29 3ndash114

Dove nyi P Horva th F Drahos D 2002 Hungary In Hurter SHaenel R (Eds) Atlas of Geothermal Resources in EuropePubl No EUR 17811 of the European Commission Office for Official Publications of the European Community Luxemburg

pp 36ndash38Erde ly M 1985 Geothermics and the deep flow-system of the

Hungarian basin J Geodyn 4 321ndash330Flohn H Fantechi R (Eds) 1984 The Climate of Europe Past

Present and Future Reidel Dordrecht Office for Official Pub-lications of the European Community Luxemburg 356 pp

Ghil M Vautard R 1991 Interdecadal oscillations and thewarming trend in global temperature time series Nature 350324ndash327

Hansen J Lebedeff S 1987 Global trends of measured surfaceair temperature J Geophys Res 92 13345ndash13372

Horva th F Dove nyi P 1991 Hungary In Hurtig E Cer-mak V Haenel R Zui V (Eds) Geothermal Atlas of Europe Hermann Haack Verlagsgesellschaft Gotha Ger-many pp 45 ndash 47

Huang S Pollack HN 1997 Late Quaternary temperaturechanges seen in world-wide continental heat flow measure-ments Geophys Res Lett 24 1947ndash1950

Jones PD New M Parker DE Martin S Rigor IG 1999Surface air temperature and its change over the past 150 yearsRev Geophys 37 173ndash199

Lamb HH 1977 Climate Present Past and Future 2 ClimaticHistory and Future Methuen London 835 pp

Landsteiner E 1999 The crisis of wine production in late six-teenth-century Central Europe climatic causes and economicconsequences Clim Change 43 323ndash334

Lane EC 1923 Geotherms of the Lake Superior copper country

J Geol 42 113ndash 122Mann ME Bradley RS 1999 Northern hemisphere tempera-tures during the past millennium inferences uncertainties andlimitations Geophys Res Lett 26 759ndash762

Pfister C Brazdil R Glaser R Barriendos M Camuffo DDeutsch M Dobrovolny P Enzi S Guidoboni E KotyzaS Militzer S Racz L Rodrigo FS 1999 Documentaryevidence on climate in sixteenth-century Europe Clim Change43 55ndash110

Racz L 1999 Climate History of Hungary Since 16th CenturyPast Present and Future Discussion Papers N 28 Centre for regional studies Hung Acad Sci ISSN 0238-2008 Pecs160 pp

Rajver D Safanda J Shen PY 1998 The climate record in-

verted from borehole temperatures in Slovenia Tectonophysics291 263ndash276

Renner F 1982 Betrage zur Gletscher-geschichte des Gotthardge- bietes und dendroklimatologische Analysen an Fossilen Hol-zern Phys Geogr vol 8 Geographisches Institut der Univer-sitat Zu rich pp 1ndash182

Rethly A 1962 Ido jarasi esemenyek es elemi csapa sok Mag-yarorsza gon 1700ig Akademiai Kiadoacute Budapest p 450 InHungarian

Rethly A 1970 Ido jarasi eseme nyek e s elemi csapa sok Mag-yarorsza gon 1701-1800ig Akademiai Kiado acute Budapest p 622In Hungarian

L Bodri P Douml venyi Global and Planetary Change 41 (2004) 121ndash133132



Rothlisberger F 1976 Gletscher-und Klimaschwankungen inRaum Zermatt Ferpe`cle und Aril Die Alp 52 59ndash152

Shen PAY Beck AE 1992 Paleoclimate change and heat flowdensity inferred from temperature data in the Superior Province

of the Canadian Shield Glob Planet Change 6 143ndash165Shen PY Wang K Beltrami H Mareschal J-C 1992 A com-

parative study of inverse methods for estimating climatic history

from borehole temperature data Palaeogeogr PalaeoclimatolPalaeoecol 98 113ndash127

Stegena L 1982 Water migration influences on the geothermics of basins Tectonophysics 83 91ndash99

Williams LD Wigley TML 1983 A comparison of evidencefor Late Holocene summer temperature variations in the North-ern Hemisphere Quat Res 20 286ndash307




signa l which can be extracted by inverse methods(eg Cermak 1971 Shen and Beck 1992 Beck et al 1992 Shen et al 1992 Bodri and Cermak 1995

1997 Huang and Pollack 1997 Rajver et al 1998 )As geothermal borehole measurements are generallyavailable from many regions on all continents theymay represent a useful tool for climatic reconstruc-tions in areas less covered by traditional climaticinvestigations

In the present study GST history is assessed from20 Hungarian boreholes This area is poorly covered by the traditional climatological data thus the geo-thermal results could provide an important supple-ment to the sparse evidence on the climate change inHungary The study is completed by a comparison of the obtained results with the GST reconstructionsfrom the neighbouring Slovakia and Slovenia histor-ical sources and the long-term meteorological meanannual series

2 Data

The first measurements of the outflowing water temperature in Hungary were carried out by Zsig-mondy V between 1866 and 1877 in the notable

drillings Harkany Margitsziget and Varosliget Thefirst borehole temperature logging in Hungary was performed by Papp K in 1919 in the boreholeVarosliget (Budapest) and the first measurementsfor heat flow density d eterminations began in the1950s (Boldisza r 1956) The present day catalogueof the temperature data in Hungary contains over 4000 temperature logs collected by Dove nyi et al(1983) Most of the borehole temperaturendashdepth pro-files were measured in the last decades of the 20thcentury at various geological settings by several

institutions and logging centres with different techni-ques and thus varying significantly in quality Major-ity of these logs were measured for the hydrologicalresources andor oil prospecting and are not suitablefor climate reconstructions Often the problem is that after drilling is completed the boreholes did not haveenough time to achieve stable thermal conditions For the classification of the existing temperature logsthere were worked out a rather rigorous data rankingcriteria (for example temperatures measured under steady state conditions temperatures measured during

drill stem tests both in water and petroleum explora-tion wells etc) and applied to Hungarian data set (Dove nyi and Horva th 1988 Horva th and Dove nyi

1991) Measurements under thermal equilibrium (thetime interval between drilling and temperature meas-urements achieved 1ndash2 years) were performed in only61 of all the boreholes However a significant part of these temperaturendashdepth profiles contains only two tofour measured points This amount is far not enoughfor the recovering of the detailed GST history Thusonly 20 from a heap of available profiles are suitablefor climate reconstructions The accura cy of the meas-urements is estimated to be 10ndash15 (Dove nyi et al1983 Horva th and Dove nyi 1991) Chosen boreh olesare regularly distributed throughout the country (Fig1) Thus results of climatic reconstructions can pro-vide also information about regional distribution of climatic changes

The selected boreholes were drilled in generallysedimentary strata All they are situated out of themain areas of advective heat disturbance in HungaryIn these areas flow of water is driven by the hydraulichead differences generally associated with topograph-ic changes andor with the Mesozoic carbonates in thePannonian basin These rocks are characterized byhigh secondary permeability occurrin g because of

intensive fracturing and karstification (Erde ly 1985) In the selected borehole sites a regional water flowsystem is related to the expellation of formation water from the pore spaces due to progressive burial andcompaction of rocks (Horva th and Dove nyi 1991) Geothermal data and model calculations have shownthat this flow is normally very slow and perturbsinsignificantly the conductive temperature field (Steg-ena 1982 Alfoldi et al 1985) Other main non-climatic causes of the nonlinearities in temperaturendash depth profiles such as topography urban heat sub-

surface heat production are also negligible As wasmentioned above boreholes were drilled in generallysedimentary so-called Upper Pannonian strata Thisformation covers the most part of the country andrepresents the Pontianndash Pliocene basin fill whichconsists of a delta-plain sequence with frequent alter-nation of sands sandstones siltstones and clayeyndash marly layers (Dove nyi et al 2002) Information onthe thermal conductivity exists for the 12 of 20 bore-holes The 20 to 50 core samples were available fromeach borehole ( Dove nyi et al 1983 Table 3) In












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borehole temp

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