J ournal ifClaciology, ViI!. 44, No. 147, 1998
Detection of abrupt changes in glacier mass balance in
the Tien Shan Mountains
M. S.
CAO
Lal1<.holl Institute ifGlaciology and Ceocryology, Chinese Academy if Sciences, Lan<.hou 730000, China
ABSTRACT.
Based on glacier mass-balance records collec ted, compiled a nd publi shed by th e World Glacie r Monitoring Service (WGMS ), an attempt is m a de h cre to
determine wh eth er there we re abrupt deca dal -scale changes in a nnu al balance on g laciers
in theTi en Sha n Mountain s. Th ere appea rs to have been a n abrupt change in the mid1970s; two-third s of the cha nge was caused by a n increase in a nnual ablation a nd the other
one-third by a dec rease in th e annual acc umulation. Thus, the change was caused m ainly
by a summ er-temperature inc rease, suppl em e nted by a d ec r ease in annu a l sn o wfall.
Climate reco rds suggest th a t thi s event, in eITect, is in response to a shift in the backg round
state of the coupl ed ocean- a tm osphere system over the Tropi cal Pacific during the mid1970s.
INTRODUCTION
Since the 1970s, abrupt cha nges in climate have been attracting increased attention. C lim a te resea rchers a re frequentl y
detecting new abrupt events at different time-scal es, analyzing their cha racteri stics, and discussing d yna mic mechanisms (G oossens a nd Berger, 1987). :For example, although
annu al temperature depa rtures over th e Northern Hemisphere have often va ri ed from p ositive to negative, or conversely, since 1851, statistical a nal ysis has shown th at there
was, in fact, a significant shift in temperature from a calder
to a wa rmer regim e in the earl y 1920s (Yam amoto and
oth ers, 1985).
Gl aciers are a n important environmental feature in high
mountain a reas. In a given mOUnLain area, climate cha ngc
directly inlluences the size, fl ow rate and even the existence
of glaciers. C onve rsely, g lacia l flu ctuations lead indirectl y to
the preser vation of records of significant changes in clim ate.
18
For exa mple, based on the a n a lysis of 5 0 reco rd s in oceansedim ent cores, stati stical studies show tha t there was a n
abrupt ch a nge in clim ate a bo ut 900 ka BI~ in th e middle of
the Pleistocene, involving worldwide cooling and an
increase in ice mass (M aasch, 1988). Mounta in gl aciers a nd
sma ll ice caps a re pa rticu la rl y sensitive to clim a te a nd it has
bee n suggested that they could be used to monitor environmental o r climatic cha nges (M eier, 1965; Barry, 1985).
Seve ra l recent studies have di scove red an abrupt change in
clim ate in the tro pica l a nd No rth Pacific O cean in the mid1970s (Trenberth, 1990; Gra ha m, 1994). H er e, an attempt is
made to d etermi ne whether this change a ITec ted glacier
mass ba la nce in the Ti en Sh a n Mounta i ns, using statistical
tests.
DATA
Because m ost glaciers a re located in spa rscly popul ated ,
cold, high-mountain areas, fi eld work is diffic ult a nd data
352
o n glacier flu ctu a ti ons are scarce. Less than about I % of
th e glaciers in th e world are surveyed, and less tha n onetenth of those surveyed have b ee n measured for mass
balance. System a tic measurem ents, starting in the mid1950s have resulted in valu abl e r eco rds (Wood, 1988). The
''''orld Glacier Moni to ring Servi ce (WGMS ) has collected
a nd compil ed ava ilabl e datase ts a nd publi shed six volumes
of data on mass balance a nd g lacier fluctuations (K asser,
1967, 1973; Muller, 1977; Haeberli, 1985, Haeberli a nd Mull er,
1988, Hae berli a nd Hoelzle, 1993).
Th e Tien Sha n Mountain s r a nge in Central Asia is
about 2100 km long and 250- 400 km wide (Fig. I). Acco rding to a recent inve ntory, there are 16490 glaciers in the
r a nge, of which only three, Ts. Tuyuksu, Ka rabatka k a nd
Urumqi No. 1, or 0.02 % of th e total, have mass-balance
records more tha n 26 yea rs long. All of the da ta used here
have bcen publi shed in th e previously menti oned WGMS
publications with modifications acco rding to th e la test corrected data (D y urgerov a nd other s, 1995) and a re g ive n in
Table 1. Th e d a ta for Urumqi g lacier No. I have b ee n reconstructed for 196 7- 78 using records from a nea rby m eteorological station. The locations and som e characteristics of th e
three glaciers di sc ussed here are shown in Figure I a nd Table
2, respectively. Although mass-bal a nce data are ava ilable in
the 'VGMS rep o rts for eight oth er glaciers nearTs. Tuyuksu,
m ost of the d a ta have been r econstructed a nd all of th e
g laciers are located in th e sam e sm a ll basin. H ence, these
a re not di scussed here.
Precipita ti o n in the Tien Sha n Mountain s is concentrated in th e spring a nd summer a nd, in fact, shifts from
spring to summer as one m oves from west to ea st. For
examplc, in the Ts. Tuyuksu bas in, 7% of the precipitation
occurs in th e w inter (December- February), 35% in the
spring (M a rch- M ay ) and 43% in the summer OuneAugust), wher eas in the Urumqi glacier No. I basin the
corre ponding p ercentages a r e 2, 18 and 66%. Thus, a significant fraction of th e acc umulalion occ urs during the ab-
Coo: Abmpt changes in glacier mass balance l1Z the Tien Shall J'vlountains
-"
"'
HI)
""
Fig. I. Locations cif the Ihree glaciers studied.
Ta.ble 1. The observational records ( mm ) of annual aCCIJI11U lotion ( C), ablation (A) and mass baLallce ( B ) on three
gLaciers il1 the Tien Shan N/ountains
56
57
58
59
60
61
62
63
64
65
66
67
57
58
59
60
61
62
63
6+
65
66
67
68
69
70
71
68
69
70
71 72
72 73
73 74
7-l 75
75 76
76 77
77
78
79
80
81
82
83
8+
85
86
87
78
79
80
81
82
83
84
85
86
87
88
RH 89
W) 90
Crul/1qi,~!a(ifl
h"arabalkak
Ts.7i,rukSll
)'im r
c
.1
/3
1070
1250
970
1090
920
870
1290
1320
11 50
1120
1280
810
1210
1130
980
970
1010
790
950
780
850
790
930
880
1100
890
11 70
710
770
11:,0
930
1090
820
920
1220
920
1390
1190
1+80
1560
850
800
1210
1080
1050
1590
1000
1020
13+0
8·H)
1300
1+10
1+00
1500
1950
2270
1+50
1510
990
158n
1720
1960
1320
1650
1270
1700
1280
IR80
- 150
330
+20
- 100
- 560
690
HO
520
50
+0
230
780
210
110
360
130
290
620
+50
720
- 1100
1+80
520
- 630
110
630
550
- 1250
550
520
:HO
610
-·,50
960
c
737
655
+7+
556
566
893
711
879
796
513
665
619
722
610
496
632
505
+H
371
+06
573
670
577
32:1
211
235
263
663
+32
791
691
730
1081
957
1280
7+2
706
7+9
752
1035
786
1265
665
801
57+
557
12+9
683
980
1285
1235
1582
107+
1034
102+
1107
1159
1807
1555
1055
111+
12+7
1087
1508
, \ 0, I
/3
c
:1
/3
3+4
291
806
86
+0
1+4
- +1
156
10
652
5+3
608
630
624
633
589
650
511
608
456
796
553
791
399
587
275
885
578
1001
+99
852
523
+07
1211
730
+59
+88
53+
551
5-15
725
1188
701
568
538
1090
1151
650
1106
87
- 188
:13
- 167
23+
2
37+
- 37+
70
+56
148
313
102
262
- 708
125
288
29
180
- 110
8+
335
- 652
o
182
1+8
53
753
51
+75
8+1
86+
1176
501
364
+47
784
9+8
1572
1292
392
682
+56
396
778
.1+5
6+7
539
625
669
503
60.1
7-l7
517
714
HI
+62
390
536
655
668
455
478
482
+7->
+62
578
596
- +5
100
83
- 612
- 669
176
- 644
+73
105
54->
52
several snow pit s. The annua l accumu lation, ablation and
mass bal a nce a re caleulated for 100 m elevalion inLervals. Similarl y, on Urumqi glacier No. I, mass bala nce is meas ured
two or three times a monlh each summer using 69 stakes
and se\'eral snow pils. rumqi glac ier ~o. I has lwO maj or
branches; on each branch lhere are one longitudina l and
eight lransverse lines of stakes. In add ili on lO such meas uremen ts, the precipitation gradienl is measured in glaeierized
areas in the vicinily of g lacier K a rabatkak, and is used, in
conjunction wilh the precipila tion data, to o btain a separate
est imale of th e mass input. This is used, logelher wilh runofT dala, to check the mass-ba lance measurements.
METHODS
Most studies detec t abrupl c ha nges in c1i male by uSll1g
slali stical tests. Generally, th e mean values of cl i matic paramelers a re used LO determ i ne whelher lhe re has been a
jump. This approac h is used on glac ier mass-bal ance data
in thi s pape r. Both the moving t-tesl UvITT) and MannKendall I-ank tesl CMKRT ) are used, and the resulls are
compared.
In th e 1\1['1''1', if the diOCI-c nce between mea ns over two
adj ace nt tim e inlervals reac h es a stipulated stati sli cal significa nce level, a n abrupl ehange is inferredlO have occurred.
Whet he r a c ha nge is delec led depend s on the c ho ice of significa nce le \"CJ. Thus, suppose a stochastic variable sequence
of a nnua l bal a nce is divided i nlO l wo sub-se ls, x I and X2 . Let
~L" Si and nj represenl the mean, variance and sample size
oflhe two sub-sels (i = l. 2), respecli\·c1y. Th e dala are lh en
a nalyzed using th e null hypothesis Ho : /JI = /J2 and th e
test slali stic, to, is ca lculated as follows:
J.Ll - /J2
to = -------,
[1
I]~
S pn;-+n:.;
where
la li o n season. Thi s makes the inter-seaso nal processes of
glaeie r mass ba la nce diffe rent from lhose on glaciers nourished prim a ril y during th e colder limes of the yea r.
A s a consequence of lhi s tempora l di slribution of accumulation, frequenl m eas urem ents are needed during lhe
summe r to ensure reli a ble estim ales oflhe seaso nal di stribulion of accumu lalion a nd a blalion (Xie a nd Liu, 1993). For
example, mass balance is m eas ured on Ts. Tuyuksu two to
four times eaeh monlh in the summer, and only once in lhe
winle r. Th ese measurements ulili ze 130- 150 Slakes and
is the sample cova ri a nce. Beca use we a re inle res led in decada l lime-scales, nl = n2 = 10. It IS ev idenl th al
to '" t(n, + '17,2 - 2) . G iven th e significance level Q a nd its
correspond ing cr ilica l value t o, the null hypoth es is Ho wi ll
be rcj ecled for I to I > to. This would suggest t h al ajump is
presenl betwee n the two neighboring sub-se ts.
Fig ure 2 is the lime se ri es of an nual balanc e from 1956353
Journal ifGlaciolofJl
~ -2~
, -------------------------------- ,
3. 5
E
E 1500
'*
8c 1000
2.5
500
~
1.0
E
-500
Oi
0.5
::s
c
c - 1000
«
0
- 1500
3.5
Year
3.0
.!:! 2. 5
:~ 2. 0
1. 0
~~ - 2
0.5
.......
.'-. ._
'...... ........ (~ c)
.~~ - 6
.;::s 'Q; - 8
1.5
" •.,
to)
E ; - 10
\
13 Oi
\
=0.05
a
=0. 10
...
o
01 E
E E -4
a
tiil ·5
2 , -____________________________-,
.Cl
(b)
l-
Fig. 2. Time series if annual balanceJrom 1956- 57 through
1989- 90for glacier Ts. Tuyuksu.
~
=0.05
1. 5
0
COl
a
2. 0
COl
2
(a)
3.0
(c)
1. 0
( a)
- 12
"'"
- 14
"'
- 1 6L---~----~--~----~--~~--~~~
b)
60 / 61
70/ 71
80/ 81
90 / 91
0. 5
0
Year
-0. 5
Fig. 3. Accumulalive curve ifannual balancefor glaciers ( a)
Ts. h ryuksu; ( b) Karabatkak; ( c) Urumqi glacier No. l.
57 through 1989- 90 for glacier Ts. Tu yuksu. Curve (a) of Fi gure 3 is the corres ponding acc umu lative cur ve for 34 years.
C urves (b) and (c) of Fig ure 3 show simi la r da ta for glac iers
K araba tka k and Urumqi glacier No. 1, resp ecti vely. It appears that there was a pro nounced cha nge in the early to
mid-1970s. It is, howeve r, not always as easy as thi s to di stinguish when accumu lati ve cur ves a re a typi cal (see L etreg uilly a nd Reynaud, 1990, fi g. 3). Th e statistical tes ts
applied here, however, can de tect such cha nges. Figure 4
shows r es ults of th e MTT test using nl = n 2 = 10 yea rs. It
is clea r th at a jump occ urs in the earl y 19 70s on glaciers Ts.
Tuy uksu a nd K a rabatk ak, and probably in the late 1970s o n
U rumqi glacier No. 1, a nd that their tests r each the sig nificance level 0' = 0.0 5 in the first two cases.
If th ere is little difference between th e m ag nitude of n i
a nd the length of the entire sequence, jumps nea r or at th e
ends of th e sequence cannot be detected. Th e non-pa r ametric MKRT test pa rtl y avoid s this weakness. It is ge nera ll y agr eed th at th e detection range of MKRT is broader
a nd the timing more precise (Goossens and B e rge l~ 1987).
The nu ll hypothes is of MKRT is H o: there is no trend
ch a nge in tb e sequence of m ass ba lance X I , X2, . .. , XN . For
each element Xi the numbers m i of elem ents Xj preceding it
(j < i) such that (X j < X i ) are co mputed. Th en, o ne
ass umes that th e test statistic dk , its exp ec ted \'alue E[d k ],
a nd va ri ance var[dk], a re as foll ows:
60/ 61
80/ 81
70/7 1
90 91
Year
Fig. 4. Abrupt change in annual balance detected using MTT
for glaciers (a ) Ts. Tityuksu; ( b) Karabatkak; (c ) UTlunqi
glacier No. 1. ( Solid horizontal lille is the critical value
corresponding 10 the significance le vel shown)
Norm aliz ing yields:
v,( d
k
)
= dk - E[dkl
Jvar[dkl
where U(dk) h as a norm al d istr ibuti on, a nd th e probability
= prob (! U !>!v,(dk ) I) can be determined using tables
or ca lcul a ti ons. If 0'0 is the sig nifica nce level of th e test (e.g.
0.05), the nu ll hypothesis i accepted or rej ected depending
on whether 0' 1 is greater o r less th an 0'0 . \ Vh en values of
V,( dk) viola te the nul l hypoth es is, th e exi ste nce of an increas ing( dk > 0) or decr easing (dk < 0) trend in the data
will be indi cated.
Fi gure 5 presents th e results of the MKRT test. Curves
Cl a re construcled from U( dk), except tha t u(d 1 ) = O. The
same procedure can be used fo r the retrogr a de seri es, where
m / represents the numbers of the elements for
X i > xj (i ::; j :::; N) . l f i' = N + 1 - i, then m i =
and
0'1
m;
u* (di )
= - 'u(d/)
(i,i'
= 1,2 , ... ,N) .
The vari a ti o n of the sequence u*(dk ) is shown by C2 in Fi gure 5. Th e approxim ate tim e of a n abrupt cha nge th at
occurs within the confidence interval is represented by the
intersecti o n of th e direc t a nd backward cur ves, Cl a nd C2.
k
dk
=L
mi
(2 ::; k ::; N)
RESULTS AND DISCUSSION
i= 1
E[d..] = k( k - 1)
4
k(k - 1)(2k + 5)
var[dJ.:] = --'----'.....:-----'72
354
The res u lts of applying th ese lechniques to th e mass-balance
records of th e three glaciers studied are li sted inTabl e 2. All
tests de tec tedju mps with sig nifica nce levels 0' = 0.05, except
that for U rumqi glacier No. I, which yielded a significa nce
Cao: Abrupt changes ing/aeier lI1ass balaure in the Tien Shan Mountains
:. 5
(a)
1.0
~I
0. 5 I \
I
\
0
V'\1
-0.5
- 1.0
11
1.5
~
- 2.0
-2.5
-3.0
(a )
3. 5
3.0
2. 5
d
~
1.0
1.0
0. 5
/_,
:::5
0
I
/I
/
3.5
1
r--.., .J\ /
~ \ /
"-
v
I1 I
I \1
\
I-<
.~
~
,'-----Cl
- 3.0
I~
(c)
I \
-0.5
I
\
\"J
- 1.0
\I
V
1.0
(c)
3.0
2. 5
a = 0.05
2.0
,1\1
~
a = 0.05
0.5
3. 5
,..' \\
I
tl
II \1 " /1
0.5
o
2.5
Ci51.5
,
-2.0
1.0
~I
3.0
«I
:; - 1 0
ii5
(b)
'E 2.0
~
u
=O . O~
1.5
(b)
2. 0
a
2.0
1. 5
V
1.0
- 1.5
0. 5
60/ 61
70/71
80 / 81
60/ 61
90 / 91
Fig. 5. Abrupt change ill anllual balance detected using
J IARTj07glaciers ( a) Ts. Ti~) ' lIksll : ( b) Aarabatkak; ( e)
L 'rllmqi glacier .\ 0. I. ( Cl alld C2 are t/ie variatioll curvesfin
for ward alld backward seqll en ces cifthe statistic ual1d u*, and
t/ie solid hori::,ol1tallille is the critical l'alue corresponding to
the significance let'el S/lO U' Il.)
kH:,1 at 0.10 o nl y. It is e\'ident that, a lthough th e a nnua l
bal ance in thi s region h as been p,-cdom in a ntl y negative
since th e 1950s. th e negative-balance rate increased after
the mid-1970s. For example, the mean balance rates fo r
g lac ie rTs. Tu y uksu are - 81 a nd - 667 mm a I water eq ui vale nt before a lld after th e jump, respecti\"ely. The difference
be t ween th em is - 586 mm a 1, bein g 1.83 times la rge r than
the mean of 374 mm a 1 for th e e ntire 34 yea rs. It a ppea rs
7c/ble 2. Detected results cifabrupt change/01,threeglaciers in
the Tiell Shan ,1{oulltaius
Gtal'irr /lam f
( I~""F(,' code)
L a t. .' N
Lon g, .' E,
A rea ( kl1l ~ 1
.JlIIl1p year t-- IKRT
.J Ulllp year t--nT I
Sign ificance le\TI
A\Tragc ma ss ba lance
Bdore ju1l1p mill a I
A\Tragc mass ba lance
f\lkrju1l1p 111m 3 I)
1•
Difkrcnce 111 m a
Pcrcc lll change ° 0 ) t
A{lrabatkak ['rulll lji glacier. \ 0. I
TI.7i!)'lIkw
( S I '()jOj5)
( SL "O508{))
( CI 'OO/O)
-13.00
77.06
3.11
1972 73
1972 73
0.05
81
+2.06
7RI8
+.56
197·, 75
197+- 75
0.05
208
,3.05
86.+9
1977 78
1977 7fl
0, 10
12
667
766
25+
586
553
110
21 2
176
183
70/ 71
80/ 81
90/ 91
Year
Y ear
UH
• J\lcan d ifference orannua l ba la nce berorc a nd arterjU1l1p year.
t Percent d ifference relative to o\'c ra ll mean annual ma ss balance.
Fig 6, AbrujJt change il1 annual accumulation delected lIsing
.M TTjor glaciers ( a ) Ts, 7i.~YUkSll . ( b) Karabatkak: ( ()
Urlll7lqi glacier, \ 0. 1. ( For explanation. see Figure 4.)
th a t he elimatic ell\'i ro nme nt in th e Ti e n Sha nt'l lo unt a in s
became wa rm er a nd dr ie r aftc r th e mid-1 970 s, a nd th at th is
chan ge was superimp osed o n th e overa ll warmer tre nd in
thi s centur y.
R esu lts of a na lyses o f th e a nnu a l acc umu la ti o n a nd
abla ti o n se ri es sepa ra tel y s how th a t th e jump yea rs a r e
1970- 71 a nd 1972- 73, respecti vely, for 11;, Tu y uksu; 1971 72
and 1974 - 75 fo r glac ie r K a rabatka k; and 1975- 76 a nd 197778 fo r U rumqi glac ie r No. I (Figs 6- 9). Note th a t th e jump
yea r for a nnua l ab lati o n coinc ides with , o r fo ll o ws by I yea r,
th a t o f an nua l ba la nce (Table 2), but fo llows that fo r acc umul a ti o n by 2- 3 years. N o te a lso (Table 3) th at a pproximately two -thirds of the d iffe re nce in a nnu a l balance is a
res ult o f a c han ge in a nnu a l abla ti o n; th e o th e r o ne-third is
du e to a c h a nge in a nnu a l acc umulatio n, Th e m ass balance
inco rp o r a tes th e effects o f both a nnu a l acc umu la ti on and
a bl a ti o n . Thus. the a brupt d ecrease in a nnua l balance fo r
th ese three g lac iers was caused more by th e va ri at io n in
a nnu a l a b la tio n th a n by th a t in acc umu la tion .
Norma ll y, snow acculllu lation is co ncentra ted in th e
winter a nd a bla tion ill th e s ummer, so a nnu a l accumu la ti o n
a nd ab la ti o n \'ar)' with winter precipitation a nd summe r
tcm pcrat u re, respectively. Howeve r, as no ted , this is not th e
case in th is part of th e Ti e n Shan ?\'[o unt a in s. The record o f
summer te mpera ture a nd a nnu a l precipitation a t the D ax igo u m e teo ro logica l statio n (43 °06' N, 86 50 ' E; 3539 m a.s.1.),
near Urumqi glac ier ~o. I, a r e show n in Table 4. Ana lyses of
th ese d a t a b y MTTa nd MKRT a re show n in Fig ures 10 a nd
11. It is cl ea r th a t th e re a re n o a brupt c h a n ges eve n a t th e
0, 10 sig nifica nce level, in e ith e r case. The d i ffe re nces in th e
D
mea ns before a nd a ft e r 1977- 78 a re on ly O,2 C a nd - 19 mm,
j
355
JoumaloJGlaciology
3.5.---------------------------------------,
1. 5r-(-a-)-----------------------------------.
0.5
o
2.0
f,\
\J \
-0. 5
I
1.5
/
\ I
1.0
~
0.5
\/
- 1.5
'"
,, ,
1\
I ,
\
~J
/v
-2.0
\
\
/
0 =0 .05
"'.J\ /
0 ,
- 0.5 \ I\...-../
I,
"J
- 2. 5
V
Cl
(b)
.
2.0
::J 1.0
I
.g 0
'" - 1.0
.~
I
3. 0
/\
\
I'
\
~
/
:5 2.0
I
u
\ .. _1
:~ 1. 0
'(;j
tii
tii - 2.0
0
- 1.0
- 3.0
~
(c )
1.5
1. 0
,
0. 5
o
/J\ 1\
I
V\
\
I
I
\
,
1.5 ( c )
1.0
A
\ ( \ 1" \ /
'-I Vi \.J
~
/1
I I
/ \
I Cl
0. 5
o
-0.5
-0. 5
- 1.0
- 1.5
Cl
0 = 0.0 5
-2.0
60/ 61
70/ 71
Year
0.5
o
80/ 81
- 0. 5
- 1.0
- 3. 0
-3.5
-4.0
o
(b)
!-o - 1.0
.~
.; - 2 . 0
S
rI) - 3 . 0
- 4.0
- 5. 0
o
0 = 0.05
V
V
- 2.5
0=0. 05
(c)
\J
70/71
Year
60/ 61
80/ 81
90/ 91
Fig. 9. Abrupt change in annual ablation detected using
MKRTjor glaciers (a) Ts. Tuyuksu, ( b) Karabatkak; (c)
Urumqi glacier No. 1. ( For explanation, see Figure 5.)
respectively. Thi s lack of eviden ce for abrupt changes may be
attributed to the unusual inter-seasonal di stribution of precipitation mentioned above. Under such conditions, both
accumulation and ablation may b e influenced by either precipitation or temperature, or both. For example, if there is
no change in precipitation in the summer, an incr ease in
temperature will not only increase ablati o n but also
decrease acc umu lation due to a lower ratio of solid to liquid
precipitation. However, if a n inc rease in tempe rature and a
decrease in precipitation occur together, th ere will be a
feed-back b etween ablation and accumulation due to the dep endence of sn owline elevation on snow acc umulation.
Thus, a lower than normal snowfall results in a higher
snowline a nd a greater increase in ablation because, due to
its lower a lbedo, ice norm a lly melts 4- 5 times fas ter than
snow (p ersonal communication from W. Tangborn, 1997).
Therefore, a lth ough no stati stically significant abrupt
Table 3. D etected results qfannual accumulation and ablation
Jor three glaciers
- 0. 2
-0.4
-0 .6
-0. 8
Glacier
- 1.0
- 1. 2
- 1. 4
- 1.6
- 1.8
I
.I
1 1
-1. 0
90 / 91
(a >
- 1.5
- 2. 0
(
- 1. 5
Fig. 7 Abrupt change in annual accumulation detected llsing
MKRTjorglaciers (a) Ts. 7i.ryuksu, ( b) Karab atkak; UTumqi glacier No. 1. ( For explanation, see Figure 5.)
Jump )'ear ,IIeall OIlIlUO/ accl/mulatioll ,IIPaI/ alll/ual ablatioll
Jor
Bifore AJter D ifference Bgore ;lfter DijJerellrf
anll11al jump jump
( % qf jump jump
(% qf
balallce
total diffj
total diffj
0 =0 .10
60/ S1
70/ 71
Year
80/ 81
90/91
Fig. 8. Abrupt change in annual ablation detected using
MTTjor glaciers (a) Ts. Tuyuksu, ( b) Karabatkak; (c)
Urumqi glacier No. 1. ( For explanation, see Figure 4J
356
/ .../',/'..../
2.5
I/ '1
I 1A
- 1.0
Cl
3.0
~
1.0
Ts. Tllyuksu
1972- 73
Karabatkak
1974-75
Urumqi No. I 1977- 78
mm
n1111
1092
667
597
915
492
519
l77 (30)
175 (30)
78 (37)
mnl
mnl
1168
874
639
1573
1258
773
410 (10)
384 (70)
134 (63)
Coo: Abrupt changes in glacier mass balance ill tlu T ien SII(I/1 Jl10untains
Tclble 4. Th e records at Daxigoll meteorological statioll
1.0
0.5
, l llIwat
Summl'r
Ifln/lerall/re
l ear
2.0
1.5
/"'enp,laIIOI/
c
(a)
0
- 0. 5
111 111
\
- \.O
58 59
59 60
60 61
61 62
62 63
63 6+
6+ 65
65 66
66 67
67 68
68 69
69 70
70 71
71 72
72- 73
73 74
N 75
75 76
76 77
77 78
78 79
79 80
80 8 1
81 82
82 83
83 B4
84 85
85 86
86 87
87 BB
88 89
89 90
~ - 1.5
3.8
+.0
3.9
+.6
+.0
+. 1
+.2
+.3
3.6
3.7
3.7
3.9
3.8
3.8
+.3
4.+
3.9
3.0
4.6
3.9
H
+.0
3.7
3.7
+.0
3.9
4.5
4.1
43
3.5
4.4
.S!
.~
;;;
0.5
(b )
\.j
I
/\
rv/I
/'J
I
0
0.5
- 1.0
a = O. la
- 1.5
- 2.0
60/ 61
70/ 71
Year
80 / 81
90/ 91
Fig. JI. Abmpt change ill ( a) summer temperature all d ( b)
anll ual jJrecij)ilatioll detected using ,Ill:RT Jor UrZllnqi
glacier. \ 0. I.
• Septe mber to Aug ust.
cha nges occ ur in a nnu a l prec ipitation a nd summer tempera ture, th e feed-bac k a mplifi es the efTec t, res ultin g in a s i g nif~
ica nt ch a nge in mass ba lance.
In th e basin of U rumqi glacier No. I, a pprecia ble
0
1.5
;iJ 1.0
I
\
j - 2.0
472.8
421.6
43+.5
+44.2
495.5
44+.2
502.3
373.8
428.0
377.6
47 1.0
380.5
465.5
489.+
35+.0
4 18.4
446.2
462.5
383.2
-f36. 1
4 17.7
360.8
448.6
1·85.9
410.7
%8.9
339.7
353.8
123 ..1
501.5
462.6
43
'/v /\,\
(a)
changes in a nnu a l prec ipita tion a nd summer te mperature
a re detec ted in 1972- 73 a nd 1976- 77 (Fi gs 10 a nd 11 ). It is
noteworth y th a t 19 76-77 is nea re r th e jump yea r fo r a nnua l
bala nce a nd a bl a tion th a n th a t [or acc umul ati o n . This again
mea ns th a t a n increase in te mperature d o minated th e
a brupt cha nge in m ass ba la nce, si nce most of th e ch a nge is
ca used by a bl a ti o n. Th e me teo ro logical reco rd s a t both
l\1ynzhilki (43 ?05' N, 77 04' E; :1017 m a.s.l.) a nd Ti e n Sha n
(41 °55' N, 78 14' E; 3614 m a.s.l.) meteorolog ica l sta ti o ns,
nea r glac ierTs. Tu )' uksu a nd Kara ba tkak, res pec ti\"c1 y, show
simil a r cha rac te ri stics (Liu and H a n, 1992). A jump in
summer tempe ra ture occ urred in 1972 73 a t ?\1y n z hilki station th at al so reac hed the 0.05 sig nificance le\·e l. Th nefore,
it seems th a t a brupt cha nges in m ass ba la nce [or these
g lac iers a rc ca used mainl y by a n increase in th e summer
tempera ture ove r th e Ti en Sh a n l\lo unta ins.
CONCLUSIONS
0.2
0.4
0.6
0.8
- 1.0
-1.2
t-- - 1.4
.!l -1.6
a =0.10
.i
£ 1.4
1.6
a =0.10
(b)
1.2
1.0
0.8
0.6
0.4
0.2
60/ 61
80/ 81
70/11
90/ 91
Year
Fig. 10. Abmj)t change in (a) sli mmer temperat ure and ( b)
annllal precipitation detected llsing JIlTT Jor Urumqi
glacier No. I.
An abrupt ch a nge in th e co upled ocea n atm os ph e re system
over the tropi ca l Pacific during the mid-1 970s was both
obsen 'ed a nd s imul ated by a ge nera l circ ul a ti o n m odel
(Gra ham, 199+). Thi s led to obvi o us cha nges in the la rgescale boreal winter circul ati on pattern over the no rth Pac ific,
m a rked by a so uthwa rd shift a nd intensificati on o f th e Alelltia n Low and o f th e preva iling wes terlies O\'e r th e mid-l atitude central and ea stern Pac ifi c. A difference in th e 700 hPa
heights bet wee n 19 70- 71 a nd 19 75- 76, a nd 1976 77 and 198182 in the Ti en Sh a n Mounta in s is co nfirmed by a t-test a t a
sig nificance I"'e l Cl: = 0.05. Thus, the abrupt c ha nge in
gl acier m ass ba la nce in th e Ti e n Sh a n M ount a ins, in e Occt,
co rres ponds to th a t event.
Va ri ati o ns in th e positi o ns of g lac ier fr ol1ls a rc o ften used
to deduce clim a te cha nge o n lon ge r time-sca les, b ecause
these da ta arc easy to coll ec t, a ltho ugh th e re p o nse lags
the clim a te c h a nge. l\;fass ba la nce, howe\'e r, reOec ts th e precedin g yea r's c li m a te. Thus, it is m o re se nsiti ve, as it directl y
lin ks a g lacie r to its clim atic e nv ironment. Thi s research
furth er sugges ts tha t monito ring m ass ba la nce ca n prO\'ide,
357
J ournal qfGlaciology
direc tl y, inform ation on abrupt cha nges in clim atic environm ents on short time-scales.
ACKNOWLEDGEMENTS
I am indebted to Pro fesso r Shi for hi s enco uragement a nd
discussions. I should a lso like to tha nk W. Ta ngborn o f the
Iceberg Moni to ring Proj ect, Universit y o[Was hing to n, a nd
D. C ayan, Clim ate R esea rch Di vision, Scripps Instituti on o[
O cea nography, for th eir deta il ed reviews a nd man y valua ble suggestions [or imprO\'emeI1l of the manuscript. I
should espec ia ll y like to th ank sincerely R. LeE. a nd A. P.
Hooke for co nscienti ous editing a nd retyping. Thi s stud y
was supported by the Chinese Academy o[Sciences proj ec t
"Basic research on d ynamic changes in the cryosphere:'
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358