CLIMATOLOGY 2015 © The Au ho s, some igh s ese ed;
exclusi e licensee Ame ican Associa ion o
he Ad ancemen o Science. Dis ibu ed
unde a C ea i e Commons A ibu ion
NonComme cial License 4.0 (CC BY-NC).
10.1126/sciad .1500561
Old Wo ld megad ough s and plu ials du ing
he Common E a
Edwa d R. Cook,
1
* Richa d Seage ,
1
Yochanan Kushni ,
1
Kei h R. B i a,
2
Ul Bün gen,
3
Da id F ank,
3
Paul J. K usic,
4
Willy Tegel,
5
Ge a d an de Sch ie ,
6
Laia And eu-Hayles,
1
Mike Baillie,
7
Claudia Bai inge ,
8
Niels Bleiche ,
9
Niels Bonde,
8
Da id B own,
7
Ma co Ca e ,
10
Richa d Coope ,
2
Ka a ina Ču a ,
11
Ch is oph Di ma ,
12
Jan Espe ,
13
Ca ol G iggs,
14
Bjö n Gunna son,
15
Bjö n Gün he ,
16
Emilia Gu ie ez,
17
K is o Haneca,
18
Samuli Helama,
19
F anz He zig,
20
Ka l-Uwe Heussne ,
21
Ju a Ho mann,
22
Pa el Janda,
23
Raymond Kon ic,
24
Nesibe Köse,
25
TomášKyncl,
26
Tom Le anič,
27
Hans Linde holm,
28
S u Manning,
14
Thomas M. Mel in,
2
Daniel Miles,
29
Bu kha d Neuwi h,
30
Ku Nicolussi,
31
Paola Nola,
32
Momchil Panayo o ,
33
Ionel Popa,
34
And eas Ro he,
35
K is ina Se igen,
28
And ea Seim,
28
Helene S a a,
36
Mi osla S oboda,
23
Te je Thun,
36
Mau i Timonen,
19
Ramzi Touchan,
37
Volodymy T o siuk,
23
Vale ie T oue ,
37
Felix Walde ,
9
Tomasz Ważny,
37,38
Rob Wilson,
39
Ch is ian Zang
40
Clima e model p ojec ions sugges widesp ead d ying in he Medi e anean Basin and we ing in Fennoscandia in
he coming decades la gely as a consequence o g eenhouse gas o cing o clima e. To place hese and o he “Old
Wo ld”clima e p ojec ions in o his o ical pe spec i e based on mo e comple e es ima es o na u al hyd oclima ic
a iabili y, we ha e de eloped he “Old Wo ld D ough A las”(OWDA), a se o yea - o-yea maps o ee- ing
econs uc ed summe we ness and d yness o e Eu ope and he Medi e anean Basin du ing he Common E a.
The OWDA ma ches his o ical accoun s o se e e d ough and we ness wi h a spa ial comple eness no p e iously
a ailable. In addi ion, megad ough s econs uc ed o e no h-cen al Eu ope in he 11 h and mid-15 h cen u ies
ein o ce o he e idence om No h Ame ica and Asia ha d ough s we e mo e se e e, ex ensi e, and p olonged
o e No he n Hemisphe e land a eas be o e he 20 h cen u y, wi h an inadequa e unde s anding o hei causes.
The OWDA p o ides new da a o de e mine he causes o Old Wo ld d ough and we ness and a ibu e pas
clima e a iabili y o o ced and/o in e nal a iabili y.
INTRODUCTION
Ins umen al obse a ions show ha he Medi e anean egion has been
d ying since he 1970s (1). Coupled clima e model simula ions om
Phase 5 o he Coupled Model In e compa ison P ojec a chi e, pe -
o med as pa o he In e go e nmen al Panel on Clima e Change
Wo king G oup 1 Fi h Assessmen Repo (2), u he sugges ha he
Medi e anean will unde go se e e and widesp ead d ying in he coming
decades as a consequence o ising g eenhouse gases (GHGs) (3). How-
e e , he ecen d ying end has been a iably a ibu ed o a mix u e o
na u al clima e a iabili y and an h opogenically o ced change (4,5),
wi h simila challenges in unde s anding bo h we ing and d ying
ends in o he pa s o Eu ope and a he a ield (6,7). This unce -
ain y a ises because he ins umen al clima e eco ds used in a ibu ion
s udies a e ela i ely sho , a e likely o be con ounded by unspeci ied
le els o GHG o cing, and a e unlikely o include he ull ange o
na u al a iabili y. In addi ion, de e mining he comple e ange o pos-
sible u u eclima es a es omclima emodels equi esknowingbo h
he esponse o changes in an h opogenic o cing and he po en ial
ange o na u al a iabili y ha willunde liei .Clima emodelsa ees-
sen ial ools o diagnosing ongoing and u u e clima e change, making
i necessa y o de e mine how well hey ep esen each o hese d i e s
o clima e a iabili y.
An ex ended eco d o na u al hyd oclima ic a iabili y om ee-
ing econs uc ed d ough and we ness be o e he ins umen al e a is
a c ucial es ima e o pas clima e a iabili y caused by bo h o ced a -
iabili y and in e nal a iabili y, which is ideal o assessing he ue
ange o hyd oclima e a iabili y in he p eindus ial pas and he de-
g ee o which clima e models p ope ly ep esen i . The No h Ame ican
D ough A las (NADA), eleased in 2004 (8), made clea ha d ough s o
1
Lamon -Dohe y Ea h Obse a o y o Columbia Uni e si y, Palisades, NY 10964, USA.
2
Clima ic Resea ch Uni , Uni e si y o Eas Anglia, No wich NR4 7TJ, UK.
3
Swiss Fede al Re-
sea ch Ins i u e WSL, Bi mensdo 8903, Swi ze land.
4
Na a ino En i onmen al Obse a o y,
Messinia 24001, G eece.
5
Ins i u e o Fo es G ow h (IWW), Uni e si y o F eibu g, F eibu g 79106,
Ge many.
6
Royal Ne he lands Me eo ological Ins i u e (KNMI), De Bil 3730, The Ne he lands.
7
Paleoecology Cen e , Queens Uni e si y, Bel as BT7 1NN, No he n I eland.
8
Na ional Museum
o Denma k, Copenhagen DK-1220, Denma k.
9
Compe ence Cen e o Unde wa e A chae-
ology and Dend och onology, O ice o U banism, Ci y o Zü ich, Zü ich 8008, Swi ze land.
10
TeSAF Depa men , Uni e si à degli S udi di Pado a, Ag ipolis, Legna o I-35020, I aly.
11
Bio echnical Facul y, Uni e si y o Ljubljana, Ljubljana SI-1000, Slo enia.
12
En i onmen al
Resea ch and Educa ion (UFB), Mis elbach 95511, Ge many.
13
Depa men o Geog aphy,
Johannes Gu enbe g Uni e si y, Mainz 55099, Ge many.
14
Co nell T ee Ring Labo a o y,
Co nell Uni e si y, I haca, NY 14853, USA.
15
Depa men o Physical Geog aphy, S ockholm
Uni e si y, S ockholm SE-106, Sweden.
16
Technische Uni e si ä D esden, Tha and D-01737,
Ge many.
17
Depa men o Ecology, Uni e si y o Ba celona, Ba celona 08028, Spain.
18
Flande s
He i age Agency, B ussels 1210, Belgium.
19
Na u al Resou ces Ins i u e Finland, Ro aniemi
FI-96301, Finland.
20
Ba a ian S a e Depa men o Cul u al He i age, Thie haup en 86672,
Ge many.
21
Ge man A chaeological Ins i u e (DAI), Be lin 14195, Ge many.
22
Jah inglabo
Ho mann, Nü ingen 72622, Ge many.
23
Depa men o Fo es Ecology, Czech Uni e si y o
Li e Sciences, P ague 16521, Czech Republic.
24
Labo Dend on, Basel 4057, Swi ze land.
25
Facul y o Fo es y, Is anbul Uni e si y, Bahcekoy, Sa iye 34473, Is anbul, Tu key.
26
Mo a ian
Dend o-Labo , B no 61600, Czech Republic.
27
Slo enian Fo es y Ins i u e, Ljubljana SI-1000,
Slo enia.
28
Depa men o Ea h Sciences, Go henbu g Uni e si y, Go henbu g SE-405,
Sweden.
29
Ox o d Dend och onology Labo a o y, Ox o d Uni e si y, Ox o d RG4 7TX, UK.
30
DeLaWi –T ee Ring Analyses, Windeck D-51570, Ge many.
31
Ins i u ü Geog aphie,
Uni e si ä Innsb uck, Innsb uck A-6020, Aus ia.
32
Dipa imen o di Scienze della Te a e
dell’Ambien e, Uni e si à degli S udi di Pa ia, Pa ia 27100, I aly.
33
Dend ology Depa men ,
Uni e si y o Fo es y, Sophia 1756, Bulga ia.
34
Fo es Resea ch and Managemen Ins i u e,
Calea Buco inei, Campulung Moldo enesc 725100, Romania.
35
Facul y o Fo es y, Uni-
e si y o Applied Sciences Weihens ephan-T iesdo , F eising 85354, Ge many.
36
NTNU
Uni e si y Museum, No wegian Uni e si y o Science and Technology, T ondheim 7012,
No way.
37
Labo a o y o T ee-Ring Resea ch, Uni e si y o A izona, Tucson, AZ 85721, USA.
38
Nicolaus Cope nicus Uni e si y, To un 87-100, Poland.
39
School o Geog aphy and Geosciences,
Uni e si y o S . And ews, S . And ews KY16 9AL, Sco land.
40
Ecoclima ology, Technische
Uni e si ä München, F eising 85354, Ge many.
*Co esponding au ho . E-mail: [email p o ec ed]
RESEARCH ARTICLE
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a se e i y and a longe i y no seen in he 19 h and 20 h cen u ies oc-
cu ed mo e equen ly in ea lie cen u ies, and his has spa ked a ange
o e o s o de e mine whe he clima e models can simula e such e en s
(9,10). He e, we p esen he Old Wo ld D ough A las (OWDA), a new
ee ing–based ield econs uc ion o pas d ough s and plu ials o e
Eu ope, No h A ica, and he Middle Eas spanning he Common E a
(CE), which will acili a e simila ad ances in unde s anding and
modeling hyd oclima e a iabili y in he Old Wo ld.
RESULTS
The OWDA is a se o yea -by-yea maps o econs uc ed summe
season [June-July-Augus (JJA)] sel -calib a ing Palme D ough Se-
e i y Index (scPDSI) (11) on a 5414-poin hal -deg ee longi ude-
by-la i ude g id (Fig. 1). The JJA scPDSI e lec s sp ing-summe soil
mois u e condi ions and is he same season econs uc ed in he NADA
(8) and Monsoon Asia D ough A las (MADA) (12). The OWDA is
based on he same eg ession-based clima e ield econs uc ion
me hod used o p oduce he NADA and he MADA. These common
p ope ies allow o di ec compa isons o he d ough a lases. The
OWDA also p o ides a longe and mo e spa ially comple e econs uc-
ion o hyd oclima ic a iabili y o e he Old Wo ld compa ed o p e-
ious es ima es based on ins umen al, his o ical, and na u al eco ds
(Supplemen a y Ma e ials). In addi ion o he ee- ing da a om li ing
ees, we assembled an excep ional amoun o his o ical, a chaeological,
and sub ossil ee- ing da a o ex end many ch onologies back a millen-
nium o mo e in ime (Supplemen a y Ma e ials). This allows us o
make in o med s a emen s abou he p ope ies o hyd oclima ic a i-
abili y du ing medie al imes in he Old Wo ld.
Dend oclima ic econs uc ions a e adi ionally alida ed h ough
compa isons o ee ing–based clima e es ima es wi h 20 h-cen u y
ins umen al da a ha ha e no been used o calib a ion (8,12). This
was pe o med as well o he OWDA by wi hholding 1901–1928 in-
s umen al scPDSI da a om he 1928–1978 calib a ion pe iod o al-
ida ion es ing (Supplemen a y Ma e ials).Howe e , he as amoun o
his o ical clima e in o ma ion om Eu ope ex ending back many cen-
u ies (13) allows o a mo e ex ensi e compa isons o OWDA econ-
s uc ions wi h eco ded d ough s and plu ials. We compa e he OWDA
o se e al his o ically documen ed ex eme hyd oclima ic e en s (wi h
addi ional compa isons shown in Supplemen a y Ma e ials), wi h em-
phasis on hose e en s ha e lec he sp ing-summe mois u e condi-
ions mos ele an o he OWDA.
The g ea d ough o 1921: On he basis o an e alua ion o ins u-
men al clima e da a no used o calib a e he OWDA, his d ough
was desc ibed as “a yea o unp eceden edly small ain all”o e la ge
pa s o he B i ish Isles, wi h he wo s de ici occu ing in sou h-
eas e n England whe e London may ha e expe ienced i s d ies yea
since 1774 (14). The OWDA map o 1921 (Fig. 2A) shows he mos
ex eme d ough occu ing in sou he n England, in acco dance wi h he
epo . I also shows se ious d ough ex ending o e mos o cen al
Eu ope bu less d y condi ions in peninsula I aly, a esul consis en
wi h o he epo s om Eu ope (15).
The g ea d ough o 1893: E alua ed again using ins umen al clima e
da a, “… he absence o ain was phenomenal”du ing he pe iod Ma ch
o June, wi h a ain all de ici g adien om 30 o 50% o no mal o e
sou he n England o 50 o 90% o no mal o e Sco land and I eland (16).
The 1893 OWDA map (Fig. 2B) shows a simila no h-sou h g adien
o ain all de ici o e he B i ish Isles and also shows he d ough ex-
ending o e con inen al Eu ope, as alluded o in his epo .
The I ish amine o 1740–1741: This e en has been a ibu ed o
unusually low win e and sp ing empe a u es in 1740, esul ing in c op
ailu es and subsequen amine (17). The OWDA is no well sui ed o
de e mining empe a u e anomalies because i p ima ily e lec s wa m
season hyd oclima e. Howe e , clima e ield econs uc ions o seasonal
p ecipi a ion om documen a y and ea ly ins umen al da a (18)indi-
ca e ha sp ing-summe ain all o e I eland in 1741 was well below
no mal ela i e o he mode n a e age. D ough o e I eland may he e-
o e ha e con ibu ed o he se e i y o he amine h ough i s nega i e
impac on ood p oduc ion in 1741. The OWDA map o 1741 (Fig. 2C)
indica es se e e d ough o e I eland ha also ex ended o e England
and Wales, consis en wi h p e iously epo ed eco d ain all de ici s (19).
The g ea d ough s o 1616 and 1540: D ough s o e Czech lands
ha e been econs uc ed om documen a y eco ds since 1090 CE, wi h
i e “ou s anding d ough e en s”(1540, 1590, 1616, 1718, and 1719)
desc ibed (20). We highligh he 1616 and 1540 d ough s he e bu no e
ha all i e ou s anding d ough e en s o e Czech lands a e well
exp essed in he OWDA (Supplemen a y Ma e ials). The 1616 d ough
began in he sp ing and con inued h oughou he summe wi h “g ea
hea , d ied-up i e s”and a ma k on a “hunge s one”on he Elbe Ri e
(20).Simila condi ionsalsoex endedin oSwi ze landandGe many.
The OWDA map o 1616 (Fig. 2D) indica es se e e o ex eme d ough
o e cen al and eas e n Eu ope, much he same as indica ed on Czech
documen a y eco ds. The 1540 d ough has been desc ibed as a “wo s -
case”e en in e ms o bo h p ecipi a ion de ici and excessi e wa m h
0˚
0˚
20˚
20˚
40˚
40˚
40˚ 40˚
60˚ 60˚
0 200 400 600 800 1000 1200 1400 1600 1800
Ch onology s a yea
Fig. 1. Map o he JJA scPDSI a ge ield (small black g id poin s) and
he 106 ch onology ee- ing ne wo k used o econs uc ion. The e
a e 5414 hal -deg ee scPDSI g id poin s. The OWDA ee- ing ne wo k ( illed
iangles shaded by s a yea ) illus a es he easonably uni o m co e age o
ch onologies ac oss he domain, excep o Russia.
RESEARCH ARTICLE
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o e cen al Eu ope ela i e o d ough s ha ha e occu ed o e he las
cen u y (21). The OWDA map o 1540 (Fig. 2E) shows he widesp ead
occu ence o mode a e o ex eme d ough s in cen al Eu ope, consis en
wi h epo s (18,19), bu no a wo s -case e en e en among he examples
shown he e.
The g ea Eu opean amine o 1315–1317: This is one o he mos
amous his o ical ca as ophes in la e medie al Eu opean his o y, a
amine caused by a mul iyea pe iod o excessi e we ness ha made
ood p oduc ion nea ly impossible (22). This plu ial ac ually began
in 1314, bu he ollowing yea was conside ed he mos ca as ophic
yea , when “… he e was uni e sal ailu e o c ops in 1315 in mos i no
all lands o Eu ope om he Py enees o Sla ic egions, om Sco land
o I aly”(22). The 1315 OWDA map (Fig. 2F) co esponds well o his
pa e n o excessi e we ness and c op ailu e and also shows he d ie
condi ions in sou he n I aly, “… which escaped he g ea c isis ha
aged no h o he Alps”(22). The OWDA now p o ides s ong e i-
dence o he hyd oclima ic condi ions o e Eu ope ha we e espon-
sible o his ca as ophe and shows i s yea ly p og ession om 1314
o 1317 in ull de ail (Supplemen a y Ma e ials).
The spa ial and empo al de ails o he OWDA econs uc ions a e a
ma ked imp o emen in ou knowledge o changing mois u e condi-
ions ac oss he Old Wo ld du ing he Common E a (Supplemen a y
Ma e ials). These ew illus a ions alone show ha he OWDA now
p o ides a new basis o he s udy o p e- and pos indus ial hyd o-
clima ic a iabili ies and hei possible causes and consequences on
he Old Wo ld. The “Medie al Clima e Anomaly”(MCA) (23)and
“Li le Ice Age”(LIA) (24) pe iods a e pa icula ly in e es ing, as well as
con o e sial, because o unce ain y o e hei condi ions ela i e o he
mode n pe iod and he deg ee o spa ial he e ogenei y in p eindus ial
clima e (25).Whiledeba eabou heexac cha ac e is ics o empe a-
u e a iabili y du ing he MCA and LIA con inues, hyd oclima ic con-
di ions emain e en mo e poo ly quan i ied. The NADA made clea
ha he MCA pe iod in No h Ame ica expe ienced se e e and p o-
longed “megad ough s”(26,27), wi h addi ional paleoclima e e idence
o ele a ed a idi y documen ed elsewhe e in he No he n Hemisphe e
(NH) (28). Ac oss Eu ope, glacie s ad anced du ing he LIA, es i ying
o a gene ally coole clima e (24), bu he hyd oclima e signa u es o he
MCA and LIA in he Old Wo ld ha e been poo ly cons ained. He e, we
use he OWDA o he i s de ailed compa ison o he spa ial pa e ns
o MCA and LIA hyd oclima e ac oss he Old Wo ld o he pe iods
1000–1200 and 1550–1750 CE, which all wi hin he gene ally accep ed
ime spans o he MCA and LIA (23,24). The speci ic pe iod chosen
he e o he MCA is also one in which a megad ough was p e iously
econs uc ed o ha e occu ed in sou he n Finland (29). The mode n
pe iod is de ined as 1850–2012. Fo each epoch, composi e maps o e-
cons uc ed scPDSI (Fig. 3A) a e shown o he ull OWDA domain
(uppe maps) as well as o jus he s a is ically signi ican (P<0.01)
egions o we ness and d yness (lowe maps). The MCA pe iod ana-
lyzed he e is signi ican ly d ie o e a la ge po ion o con inen al
no h-cen al Eu ope and sou he n Scandina ia han ei he he LIA
0˚ 16˚ 32˚
36˚
48˚
60˚
0˚ 16˚ 32˚ 0˚ 16˚ 32˚
36˚
48˚
60˚
1921 1893 1741
0˚ 16˚ 32˚
36˚
48˚
60˚
0˚ 16˚ 32˚ 0˚ 16˚ 32˚
36˚
48˚
60˚
1616 1540 1315
ABC
DEF
–6 –4 –2 0 2 4 6 –6 –4 –2 0 2 4 6 –6 –4 –2 0 2 4 6
Fig. 2. OWDA maps o known yea s o hyd oclima ic ex emes. (A o F) The maps a e p esen ed in e e se ch onological o de based on documen a y
clima e eco ds: om he bes yea s eco ded by ins umen al clima e eco ds [1921 (A) and 1893 (B)] o he lesse known yea s [1741 (C), 1616 (D), 1540(E),
and 1315 (F)]. See he ex o de ails and e e o Supplemen a y Ma e ials o mo e examples o his o ical d ough s om documen a y eco ds.
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0˚ 16˚ 32˚
36˚
48˚
60˚
0˚ 16˚ 32˚ 0˚ 16˚ 32˚
0˚ 16˚ 32˚ 0˚ 16˚ 32˚ 0˚ 16˚ 32˚
36˚
48˚
60˚
−1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0
−1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0
36˚
48˚
60˚
36˚
48˚
60˚
1000−1200 1550−1750 1850−2012
>99% CL >99% CL >99% CL
MCA LIA MOD
–4
–2
0
2
4
900 1100 1300 1500 1700 1900
scPDSI
Yea
MCA LIA MOD
B
A
scPDSI scPDSI scPDSI
Fig. 3. Compa ison o mean scPDSI ields in he OWDA du ing pe iods associa ed wi h he MCA, LIA, and mode n pe iod (MOD). (A)Themean ields
we e calcula ed o e he ime in e als indica ed, and he a eas in hose ields wi h signi ican mean anomalies o we ness o d yness (p< 0.01, wo- ailed,
co ec ed o lag −1 au oco ela ion) a e indica ed in he middle se o maps. The a ea o maximum d yness du ing he MCA pe iod is indica ed by he yellow
ec angle in he lowe MCA map. (B) A e age o OWDA econs uc ions om wi hin his ec angle. I con i ms he d ie condi ions du ing he MCA pe iod and
also shows he occu ence o an ex ao dina y megad ough in he mid-15 h cen u y. CL, con idence le el.
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o mode n pe iod, conside ably adding o he p e ious epo o an
MCA megad ough in sou he n Finland (29), and i now mo e com-
ple ely de ines he spa ial pa e n andex en o d ynessdu ing ha ime.
In con as , he Romania and Uk aine egions o eas e n Eu ope ha e
mo e simila pa e ns o d yness, and no he n Fennoscandia and Russia
ha e mo e simila pa e ns o we ness, in all h ee epochs. No ably, he
o e all iming o MCA d yness in no h-cen al Eu ope is consis en
wi h ha desc ibed o la ge a eas o No h Ame ica (26,27)(seela e
discussion).
A summa y o he his o y o d ough and we ness since 870 CE in
heco e egiono OldWo ldMCAd ough (Fig.3A,yellow ec angle)
is p esen ed in Fig. 3B. The o e all mean ± 1se o is −0.44 ± 0.04 scPDSI
uni s om he expec ed mean o ze o o he 1928–1978 calib a ion
pe iod, which e lec s he gene al endency o d ie condi ions in he
p eindus ial pas . In con as , he mos ecen pe iod (1998–2012) has
been anomalously we (+0.97 ± 0.24). I is necessa y o go back o 1721–
1739 o ind a we e pe iod o compa able du a ion (+1.55 ± 0.24). As a
ela i e index o d ough , scPDSI has a high deg ee o spa ial compa a-
bili y ac oss a b oad ange o p ecipi a ion clima ologies (30). This allows
us o compa e his d ough o ano he econs uc ed medie al mega-
d ough occu ing a a ound he same imeinwes e nNo hAme ica
(26). The 1000–1200 CE megad ough o e no h-cen al Eu ope has a
econs uc ed mean o −0.72 ± 0.10 scPDSI uni s. By compa ison, he
wo s megad ough in he Cali o nia and Ne ada egions o he NADA
(26) las ed om 832 o 1074 CE (−0.84 ± 0.09, calcula ed a e adjus ing
he mean o he Cali o nia/Ne ada se ies o ma ch ha o he no h-
cen al Eu ope se ies o e hei 870–2005 common in e al). Thus, in
e ms o ela i e d yness as modeled by he scPDSI, his MCA mega-
d ough in he OWDA is compa able o one o he mo e excep ional
MCA megad ough s in he NADA.
Besides he MCA, Fig. 3B also e eals he occu ence o a mid–15 h-
cen u y megad ough in no h-cen al Eu ope. The mos in ense d ough
phase las ed o 37 yea s om 1437 o 1473 CE (−1.84 ± 0.20), wi h only
wo isola ed yea s o posi i e scPDSI. The iming o his megad ough is
simila o ha o he wo s d ough econs uc ed o ha e occu ed o e
he pas 1000 yea s in he sou heas e n Uni ed S a es (27). This sugges s
he exis ence o some common hyd oclima e o cing ac oss he No h
A lan ic, pe haps ela ed o A lan ic Ocean sea su ace empe a u e
a ia ions and/o he No h A lan ic Oscilla ion (31,32). Finally, a hi d
megad ough occu ed om 1779 o 1827 (−1.34 ± 0.16). This pe iod has
a subpe iod o “majo long-du a ion d ough ”(33) om 1798 o 1808
(−1.89 ± 0.38) in England and Wales iden i ied om ea ly ins umen al
NADA
MADA
OWDA
La i ude
A NHDA egions
–4
–2
0
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
2
4
Z-sco es
B NHDA a e ages
Yea s
Longi ude
0˚
−150˚ −100˚ −50˚ 50˚ 100˚ 150˚0˚
20˚
40˚
60˚
Fig. 4. The NHDA based on he OWDA, NADA, and MADA. (A) The empe a e la i ude egions o d ough a lases wi hin he dashed boxes a e em-
phasized o pu poses o compa ison because no all d ough a lases ha e bo eal ( o example, MADA) o opical ( o example, OWDA) econs uc ions.
(B) The o iginal annually esol ed d ough econs uc ions in each egion we e a e aged om 1000 o 1989 CE, ans o med in o s anda d no mal de-
ia es (Zsco es), and low pass– il e ed o emphasize a iabili y ha was >30 yea s in du a ion. The low pass– il e ed a e age se ies we e eno malized
o elimina e any di e en ial weigh ing by egion and a e aged o p oduce he NHDA eco ds (no eno malized) shown in black.
RESEARCH ARTICLE
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and his o ical clima e in o ma ion. I is also he d ies pe iod wi hin he
longe epoch (1779–1827) o pe sis en ly d ie - han-a e age condi ions
o e no h-cen al Eu ope. Mo e gene ally, Fig. 3B e eals he exis ence
o la ge-ampli ude decadal o cen ennial hyd oclima e a iabili y o e
Eu ope and shows ha , like No h Ame ica, megad ough s in he Old
Wo ld we e no es ic ed o jus he MCA pe iod. In compa ison, hyd o-
clima e a iabili y o e he 20 h cen u y, al hough la ge, does no ap-
pea unp eceden ed in ampli ude o end. Isola ing signals o ecen
GHG-induced hyd oclima e change om his complex eco d o
na u al a iabili y will be challenging.
DISCUSSION
The OWDA g ea ly expands ou unde s anding o he spa io empo al
his o y o d ough s and plu ials in he Old Wo ld. I con i ms he oc-
cu ence o an MCA megad ough in no h-cen al Eu ope, i s no ed
in sou he n Finland (29), which is simila in iming, du a ion, and el-
a i e in ensi y o ha ound in he NADA o he wes e n Uni ed S a es
(26). This inding signi ican ly adds o he ealiza ion ha NH d ough s
we e mo e p olonged du ing he MCA compa ed o he 20 h cen u y,
wi h li le unde s anding as o why. In addi ion, he example maps illus-
a e i s conside able ele ance o s udies o hyd oclima e impac on Old
Wo ldsocie iesandcul u eso e heCommonE a.
The OWDA is an impo an new ad ancemen owa d achie ing a
ull and consis en spa ial co e age o hyd oclima ic a iabili y ac oss
he NH land a eas du ing he Common E a, one o he p ima y goals
o Kau man and he PAGES 2k Conso ium (34). Figu e 4 shows p o-
g ess owa d he comple ion o a “No he n Hemisphe e D ough A las”
(NHDA) o he empe a e la i ude egions o he OWDA, NADA, and
MADA (Fig. 4A). This gi es us an oppo uni y o compa e hyd oclima ic
a iabili y be ween con inen s on a hemisphe ic basis back o he MCA
o he i s ime.
A i s compa ison, based on no malized a e ages o econs uc ed
d ough s smoo hed o emphasize >30-yea ime scales o a iabili y
(Fig. 4B), shows li le commonali y in he iming o we and d y epochs
be ween d ough a las egions a he con inen al scale o e he pas
1000 yea s (a e age = 0.05). Howe e , he e a e se e al pe iods o dis-
inc an iphasing be ween egions, especially be ween he NADA and
he MADA, which none heless sugges s some dynamical links be ween
hem. The NHDA a e age has also shown a long- e m posi i e end
om d ie o we e condi ions o e he empe a e la i udes o he NH
since he MCA. The addi ion o he OWDA o he NADA and MADA
hus allows o mo e comple e in es iga ions o a mosphe e-ocean
dynamical in luences on he hemisphe ic pa e ns o hyd oclima e
a iabili y o e he Common E a. The use o mul iple clima e ield econ-
s uc ions (spa ially and ully da a-independen ) ep esen ed by he
OWDA, NADA, and MADA should be e cons ain he modes o cli-
ma e a iabili y esponsible and g ea ly imp o e ou unde s anding o
he causes o hyd oclima ic a iabili y a in e annual o cen ennial ime
scales. Fu he mo e, comple ion o he OWDA, oge he wi h a ailable
simula ions o he las millennium, now allows us o de e mine whe he
s a e-o - he-a clima e models in he NH con ain ealis ic hyd oclima e
a iabili y a in e annual o cen ennial ime scales [see Sme don e al.
(35) o a No h Ame ican example]. This knowledge is essen ial o
assessing whe he models can co ec ly ep esen he ange o u u e
hyd oclima es, including we and d y ex emes, ha combine o ced
change wi h con inued na u al a iabili y.
MATERIALS AND METHODS
The scPDSI da a used o econs uc ion (11) a e based on g idded
Clima ic Resea ch Uni Time Se ies (CRU TS) mon hly empe a u e
and p ecipi a ion da a (36) upda ed o e sion CRU TS 3.21 and co e -
ing he pe iod 1901–2012. We examined he changing densi y o p e-
cipi a ion s a ions a ailable o in e pola ion on o he CRU TS 3.21
p ecipi a ion g id be o e 1950 and ound i o be s able back in ime o e
mos o he OWDA domain (Supplemen a y Ma e ials). The g ea es
excep ionwas oundinTu keyand heMiddleEas ,whe eli lelocal
p ecipi a ion s a ion da a we e a ailable be o e 1930 o in e pola ion o
he hal -deg ee g id. This is no desi able o e alua ing econs uc ion
skills in hose egions o e he 1901–1927 eg ession model alida ion
pe iod. Howe e , i is unlikely o ad e sely a ec he ee- ing econs uc-
ions hemsel es because he 1928–1978 calib a ion pe iod used o
p oduce he econs uc ions ba ely o e laps wi h he pe iod o educed
local p ecipi a ion da a co e age. The co ela ion decay leng h (CDL) o
he scPDSI ield was also e alua ed and ound o be ~800 km, on a -
e age, bu wi h conside able la i udinal a iabili y. This in o ma ion was
use ul o objec i ely de ining he sea ch adius used o ind ee- ing
ch onologies o econs uc ion o pas d ough s (see la e discussion
and Supplemen a y Ma e ials o de ails).
The ee- ing da a used o p oduce he OWDA came om he In-
e na ional T ee-Ring Da a Bank and om con ibu ions by Eu opean
dend och onologis s, including a la ge quan i y om he dend oa ch-
aeology communi y. Inco po a ing a chaeological ee- ing da a in o he
ee- ing ne wo k, a e upda ing wi h mode n ee- ing da a om app o-
p ia e younge li ing ees (37), enabled he econs uc ions o be
ex ended back a millennium o mo e o e mos o he OWDA domain.
The esul ing ee- ing ch onologies we e de eloped o clima e econ-
s uc ion using he newes “signal- ee”me hods o ee- ing s anda diza-
ion (38,39), wi h emphasis on p ese ing long- e m a iabili y due o
clima e. Because o conside able a ia ion in he segmen leng hs o he
a chaeological ee- ing se ies in each o hose ee- ing da a se s and he
associa ed di icul y in p ese ing long- e m clima e a iabili y because o
“segmen leng h cu se”(40), a modi ied signal- ee egional cu e s an-
da diza ion (SF-RCS) (39) me hod was de ised and used (see Supple-
men a y Ma e ials o a de ailed desc ip ion o how RCS was pe o med).
The clima e ield econs uc ionme hodused op oduce heOWDA
is he poin -by-poin eg ession (PPR) me hod (41), wi h an ex ension
o he p ocedu e p oducing ensembles o clima e econs uc ions (12,42).
The OWDA econs uc ion p esen ed he e is he mean o eigh ensem-
ble membe s, wi h each membe being based on he weigh ing o each
ee- ing ch onology used in PPR by some powe o i s co ela ion wi h
scPDSI (42). The ini ial sea ch adius used by PPR o loca e ee- ing
ch onologies o econs uc ing scPDSI a each g id poin was se o
1000 km, a small enla gemen o e he es ima ed CDL (800 km) o
he ins umen al scPDSI da a o accoun o some o he i egula spacings
o he ee- ing ch onology ne wo k shown in Fig. 1.
A alue-added ou come o PPR was he abili y o e alua e he clima e
sensi i i y o he ee- ing ch onologies used o scPDSI econs uc ion.
This e alua ion, pe o med h ough a simple co ela ion analysis, conclu-
si ely demons a ed he o e all mois u e sensi i i y o he ee- ing
ch onologies o e mos o he OWDA domain, a esul ha is highly
consis en wi h an independen e alua ion o he clima e esponse o
ee- ing ch onologies in Eu ope (43). A high ele a ions in cen al Eu-
ope and a high no he n la i udes in Fennoscandia, he le el o mois-
u e sensi i i y does diminish and is inc easingly eplaced by sensi i i y
RESEARCH ARTICLE
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o g owing-season empe a u es. This change in clima e sensi i i y has
also been desc ibed by Babs e al.(43). The success ul econs uc ion o
d ough s in Fennoscandia, using a mix u e o mois u e- and empe a u e-
limi ed ee- ing eco ds (44), indica es ha his change in clima e sensi-
i i y is no a se ious issue ( e e o Supplemen a y Ma e ials o de ails).
SUPPLEMENTARY MATERIALS
Supplemen a y ma e ial o his a icle is a ailable a h p://ad ances.sciencemag.o g/cgi/
con en / ull/1/10/e1500561/DC1
In oduc ion
OWDA as a scien i ic ad ancemen o e p e ious wo k
G idded mon hly scPDSI a ge ield
OWDA ee- ing ne wo k
Clima e sensi i i y o OWDA ee- ing ch onologies
Valida ion o OWDA ee- ing clima e esponse
Augmen ing ee- ing ch onologies wi h his o ical ee- ing da a
S anda dizing OWDA ee- ing da a o clima e econs uc ion
S anda dizing OWDA his o ical/mode n ee- ing da a
Es ima ing low- o medium- equency a iance e en ion
Poin -by-poin eg ession
Compa isons wi h Pauling sp ing-summe p ecipi a ion econs uc ions
Addi ional alida ion es s o he OWDA
Re e ences
Table S1. Lis o ee- ing ch onologies used o p oducing he OWDA.
Fig. S1. Map o he OWDA domain showing 5414 hal -deg ee g id poin s o JJA scPDSI (small
black do s) and he 106 annual ch onology ee- ing ne wo k ( ed and blue iangles).
Fig. S2. Maps, by decade (up o 1950), o he changing densi ies o p ecipi a ion s a ions (solid
ed do s) a ailable o in e pola ion on he hal -deg ee egula g id used o p oduce he CRU
TS p ecipi a ion ield (h p://badc.ne c.ac.uk).
Fig. S3. Compa isons o calib a ion pe iod (1928–1978) and alida ion pe iod (1901–1927)
scPDSI a e ages and hei a iances.
Fig. S4. S a is ical p ope ies o g idded summe scPDSI da a o e he 1928–1978 calib a ion
pe iod and es s o no mali y using a simple and obus es o no mali y based on join use o
skewness and ku osis (69).
Fig. S5. CDL be ween 5414 g id poin s o summe scPDSI used o econs uc ion o e he
OWDA domain.
Fig. S6. Summa y maps o co ela ions be ween summe scPDSI and he ee- ing ne wo k o e
he 5414 g id poin s o he OWDA domain calcula ed o he 1928–1978 calib a ion pe iod, using
he PPR p og am in he same way ha i was used o p oduce he OWDA econs uc ions.
Fig. S7. Example o a his o ical/mode n ee- ing ch onology om no heas e n F ance
de eloped by he i e a i e p ocedu e desc ibed in he ex .
Fig. S8. O e lay plo s o To ne ask powe spec a ( equencies om 0 o 0.1) o di e en
de ending op ions be o e (RCS/SSD) and a e (SF-RCS/SSD) he applica ion o he signal- ee
me hod o he da a using he same cu e- i ing op ions: Op 0—RCS de ending (designed o
p ese e he mos low- o medium- equency a iance); Op 1—nega i e exponen ial/linea
de ending (mono onic noninc easing, leas lexible SSD op ion); Op 2—cubic smoo hing spline
de ending based on he median segmen leng h o he da a (mode a ely da a-adap i e, ixed
in e media e lexibili y); and Op 3— he F iedman a iable span smoo he (locally adap i e, e y
lexible).
Fig. S9. Example o he wo-s age SF-RCS me hod applied o he his o ical/mode n Que cus species
(QUSP) ee- ing da a o no heas e n F ance used as an example by Aue e al.(48).
Fig. S10. Addi ional low- o medium- equency a iance e ained in he his o ical/mode n ee- ing
ch onologies using he wo-s age SF-RCS p ocedu e.
Fig. S11. Calib a ion and alida ion s a is ical maps o he eigh -membe ensemble-a e age
OWDA econs uc ions.
Fig. S12. Co ela ions o OWDA JJA scPDSI econs uc ions wi h Pauling sp ing-summe p ecipi a ion
econs uc ions p ima ily econs uc ed om long ins umen al and his o ical clima e indices (18).
Fig. S13. Compa ison o OWDA and Pauling maps o 1540 (“yea -long unp eceden ed
Eu opean hea and d ough ”)(21).
Fig. S14. Maps o excep ional d ough s in Czech lands (20).
Fig. S15. Maps o he g ea Eu opean amine (22).
Fig. S16. OWDA mean and median maps o nine no ewo hy 17 h-cen u y d ough s o e
England and Wales: 1634, 1635, 1636, 1666, 1667, 1684, 1685, 1694, and 1695 (33).
Fig. S17. OWDA mean and median maps o eigh no ewo hy O oman Empi e d ough s:
1570, 1591, 1592, 1594, 1595, 1607, 1608, and 1610 (107).
Fig. S18. OWDA mean and medianmaps o 12 no ewo hy p e-1450 his o icald ough s in England
and Wales: 1084, 1129, 1136, 1222, 1242, 1252, 1263, 1272, 1284, 1288, 1305, and 1385 (110).
Re e ences (45–110)
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Acknowledgmen s: Re iews o ea lie d a s o his pape by K. Anchukai is, M. Cane, B. Cook,
J. Sme don, and A. P. Williams imp o ed i s quali y and a e g ea ly app ecia ed. Funding: We
hank he Na ional Oceanic and A mosphe ic Adminis a ion Clima e Change Da a and De ec-
ion P og am o suppo ing his p ojec (awa d NA10OAR4310123) and he Na ional Science
Founda ion Ea h Sys em His o y P og am (awa ds 0075956 and ESH0317288), ATM GEO/ATM Pa-
leoclima e P og am (awa d 0758486), and awa d 1103314 o addi ional long- e m suppo in
de eloping his esea ch in he Medi e anean egion. Au ho con ibu ions: E.R.C. was ully e-
sponsible o da a p ocessing, s a is ical analysis, and p oduc ion o heOWDA. G. .d.S. p o ided he
PDSI a ge ield da a. R.S. and Y.K. helped guide he de elopmen o he OWDA and wo ked on
clima e dynamics in e p e a ion. W.T. and U.B. spea headed he con ibu ion o ee- ing da a used
in he OWDA. K.R.B., D.F.,and P.J.K. con ibu ed da a and c i ically e iewed ea lie d a s. The emain-
ing coau ho s con ibu ed ee- ing da a o he e o . Compe ing in e es s: The au ho s decla e
ha hey ha e no compe ing in e es s. Da a and ma e ials a ailabili y: All da a needed o
e alua e he conclusions in he pape a e p esen in he pape and/o he Supplemen a y
Ma e ials. The OWDA econs uc ions a e a chi ed wi h associa ed me ada a (www.ncdc.noaa.
go /da a-access/paleoclima ology-da a/da ase s/clima e- econs uc ion) o ou ine public access
and use.Asecondpublic access si ewill be se up a he In e na ional Resea ch Ins i u e o Clima e
and Socie y/Lamon -Dohe y Ea h Obse a o y Clima e Da a Lib a y (h p://i idl.ldeo.columbia.
edu). The OWDA was made possible h ough he ee- ing da a (mos o hem unpublished)
p o ided by he dend och onological communi y, which is engaged in a ious aspec s o Old
Wo ld ee- ing esea ch. The a ailabili y o dend oa chaeological da a om Eu ope enabled
he OWDA o be ex ended back o e mos o he CommonE a, which would ha e been impossible
o do o he wise, and he newly a ailable g idded scPDSI da a om he Royal Ne he lands Me e-
o ological Ins i u e (h p://climexp.knmi.nl) p o ided he high-quali y ins umen al da a o calib a-
ion. O he ee- ing da a came om he In e na ional T ee-Ring Da a Bank (www.ncdc.noaa.
go /da a-access/paleoclima ology-da a/da ase s/ ee- ing), om A. Billamboz (Dend olab A -
chaeological Se ice, Baden-Wü embe g, Ge many), and om he a chi ed ee- ing da a
con ibu ed by K. Tye s and I. Tye s o he ADVANCE-10K p ojec (h p://hol.sagepub.com/con-
en /12/6/639.abs ac ). Addi ional da a ela ed o his pape may be eques ed om he au ho s.
Lamon -Dohe y Ea h Obse a o y con ibu ion numbe 7938.
Submi ed 4 May 2015
Accep ed 4 Augus 2015
Published 6 No embe 2015
10.1126/sciad .1500561
Ci a ion: E. R. Cook, R. Seage , Y. Kushni , K. R. B i a, U. Bün gen, D. F ank, P. J. K usic, W. Tegel,
G. an de Sch ie , L. And eu-Hayles, M. Baillie, C. Bai inge , N. Bleiche , N. Bonde, D. B own,
M. Ca e , R. Coope , K. Ču a , C. Di ma , J. Espe , C. G iggs, B. Gunna son, B. Gün he ,
E. Gu ie ez, K. Haneca, S. Helama, F. He zig, K.-U. Heussne , J. Ho mann, P. Janda, R. Kon ic,
N. Köse, T. Kyncl, T. Le anič, H. Linde holm, S. Manning, T. M. Mel in, D. Miles, B. Neuwi h,
K. Nicolussi, P. Nola, M. Panayo o , I. Popa, A. Ro he, K. Se igen, A. Seim, H. S a a, M. S oboda,
T. Thun, M. Timonen, R. Touchan, V. T o siuk, V. T oue , F. Walde , T. Ważny, R. Wilson, C. Zang,
Old Wo ld megad ough s and plu ials du ing he Common E a. Sci. Ad . 1, e1500561 (2015).
RESEARCH ARTICLE
Cook e al. Sci. Ad . 2015;1:e1500561 6 No embe 2015 9o 9
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