2.9

BulletinofGlaciologicalResearch20（2003）29−40⑥JapaneseSocietyofSnowandIce

GJacierdistributioninthe Himalayasandglaciershrinkagefrom1963to1993in the Bhutan
Himalayas
Karmal，YutakaAGETA2，Nozomu NAITO2，ShujiJWATA3and HironoriYABUKl4
1GeologicalSurveyOfBhutan，P．0．Box173，Thimphu，Bhutan

2GraduateSchoolofEnvironmentalStudies，NagoyaUniversity，Nagoya464−8601Japan
3DepartmentofGeography，TokyoMetropolitanUniversity，Hachioji，Tokyo192−0397Japan
4FrontierObservationalResearchSystemforGlobalChange，Yokohama236−0001Japan（ReceivedSeptember9，2002；RevisedmanuscriptreceivedNovember8，2002）

Abstract

Himalayan Range extends more than2，000km from east to northwest；influence of summer

monsoononglaciersdiffersregionally．Glacierdistributioninthewhole Himalayasandterminal／

arealvariations ofdebris−freeglaciersintherecent30yearsinBhutanare analyzedfromnewly

publishedinventoriesofIndia，eaStNepalandBhutan，tOpOgraphicmapsandsatelliteimages．
Lowestelevationsandestimatedequilibriumlinealtitudes（ELAs）ofglaciersintheeasternhalf

OftheHimalayaslocatedatthesimi1arlatitudesdescendtowardeastfromNepalviaSikkim−Bhutan
toArunachal．TheestimatedELAsintheeasternHimalayasatthelowerlatitudesarenotsomuch

differentfromthoseinHimachal・GharwalinthewesternHimalayasatthehigherlatitudes，thoughthosedescendfromHimachal−GharwaltoKashmirtowardnorth（west）．Thesetendenciesofglacierdistributionappear，Sincemonsoonprecipitationincreasestowardeastern／southernpartfromwest−
ern／northernpartintheRange，andthehigherprecipitationincreasesaccumulationandaccompanied
Cloudyweatherdecreasesablation．

AlmostallglaciersmeasuredinthewholeHimalayashavebeenretreatingintherecentdecades．
AveragedannualterminalretreatofglaciersinBhutanishigherthanthatinNepal．Anincreasing

trendofglacierretreatisfoundinNepalfromwesttoeast，inNepalandBhutanfromnorthtosouth．

Thesetendenciesofglaciervariationareexplained，Sinceglaciersvarymoreinplaceswiththehigher

precipitation and the warmer temperature due to mass balance characteristics of the summer−
accumulationtypeglaciers．

1．lntroductjon

The Himalayan Range extends morethan2，000
km alongthe direction ofeast−nOrthwest andmany
glaciersin the range are shrinking recently．Since
most ofannualprecipitation fallsinsummer due toFig．1），distribution and variation of the glaciers

dependontheirlocationsintheHimalayas．
For the comparative study on glaciersinthe
eastern and western Himalayas，information on theglaciersintheeasternmost Himalayaswasspecially

SCarCe．In Bhutan，the firstglacier observation was
theIndian summer monsoon，the summer precipita− brieflymadeinthe1960s by Gansser（1970）．In1996
tionisthemainsourceofannualaccumulationonthe
after the blank for many years，Phuntso Norbu，glaciers and characterizes the glacier regime in the
Himalayas．Themonsooncontributesnotonlytothe
accumulation，butalsotothedecreaseofablationdue
to accompanied cloudy weather during the melting
season which provides the conditions with low airtemperatureandlowinsolationwithadditionaleffectOf highalbedo by new snow．Such glaciers were

Division of Geology andMines，Bhutan prepared aninventoryofglaciersandglacierlakesinthenorthernpartofBhutanusingsatelliteimagesof1989and1990

andtoposheets of1962／63．Theinventorywas publi−

ShedwithadditionaldataandeditionbytheGeologi−

CalSurvey of Bhutan（1999）．On the basis of theseStudies，eXpanSion ofproglaciallakes and retreat ofglaciersinrecentdecadesinBhutanwerereportedby

Classified as the summer−aCCumulation type by
AgetaandHiguchi（1984）．SincethemonsoonprecipiT thepresentauthors（Agetaetal 2000）withtheirfield
tationis much morein the eastern part than thedata．Mostrecently，aninventoryoftheglaciersand
WeSternpartandinthesouthernpartthanthenorth・glacierlakesin Bhutan was published byICIMOD
ern partinthe Himalayan Range（e．g．Eguchi，1994，（InternationalCenterforIntegratedMountainDevel−

30

BulletinofGlaciologicalResearch

10

ー「▲B−B

正
盲
王
U
O
；
ロ
三
石
巴
d

3

10

2 0

0

一
l

正

0

8 −0

9 0

Lo叩汗ude（Eosり10bFig．1 Distribution of mean annualprecipitation aroundthe HimalayanRange（afterEguchi，1994）．
ThemainrangeislocatedbetweenthelineA・A andthe
WeSternpartOfthelineC−C tothelineB−B ．
Averagedyearsare1975−1980forBhutan，1976−1980forNepaland195ト1980forothers．

opment，2001）as part oftheir workin Hindu Kush
−Himalayanregion．

glaciers among tota15243glaciersinIndia．In thepresentstudy，Onlythedetailedglacierdatatabulated
inthisinventoryareused．
2）Datafortheglaciersineastern NepalHimalayas

2．Data and method

variations of the glaciers since the Little Ice AgeWith the background of increasing data of theeasternHimalayasmentionedaboveandthoseofthe（85．OOE・88．20E）aretakenfromtheinventorybyAsahi
Whole Himalayasintroducedinthenextchapter，thepresent studyhas been made．Purposes of the study（1999）．GlaciersinwesternNepalarenotincludedin
are to clarify the characteristic tendency of glacier thisinventory．Here the similar data of glaciersmentionedintheIndianinventorycanbefoundexcept
distribution in the whole Himalayas under different
mean elevation of accumulation area and that of
monsoonclimates，andtoclarifytheglaciervariation
inrecentdecadesin Bhutanwhere the monsoonpre−
ablationarea，1ength，meanWidth，Surfacearea，AAR，
mean depth，VOlume．In addition，the maximum alti−
Cipitationis much more，COmparingwithglaciersin
tudeofdebris−COVeredarea，theestimatedequilibrium
Nepal．

Data bases used for the present study and themethod are as follows：line altitude（ELA）and others are given．Terminal（LIA）andfrom1959to1992arealsogiven．TheELA

WaSdeterminedonthebasisofmorphologicalcharac−

teristics of glaciers；the terminalpositionsin LIA，

1）DatafortheglaciersintheIndian Himalayas aretaken from theinventory by GeologicalSurvey of

1959and1992wereidentified by the moraines，thetoposheets and the aerialphotographs，reSpeCtively

elevations，meanelevationofaccumulationarea and3）For the generalanalysis on theglaciersin the
BhutanHimalayas，dataaretakenfromtheinventory

VOlumeandthe6digitmorphologicalclassificationof

for meanelevationofaccumulation area and that ofIndia（1999）．Heredetaileddata onlocation（1atitude
andlongitude），Orientation，the highest andlowest（Asahi，1999）．

that of ablation area，length，meanwidth，Surface byICIMOD（2001）．Here almost alltheinformationarea，theaccumulationarearatio（AAR），meandepth，
mentionedintheIndianinventorycanbefoundexcept
theglaciers（UNESCO／IASH，1970）aregivenfor1205 ablatiorlarea，meanwidthandAAR．

3J

Karma（ZJαJ．

4）FortheanalyzedglaciersinBhutan，SOmeOfdata

CE＝（月E十比Ac）／2，
AE＝（エE十比Aα）／2，andEエA＝（ELAc＋且乙A（Z）／2，

areusedfromtheinventorybyGeologicalSurveyof

Bhutan（1999）．Heretheinformationislimitedtothe
lowest elevation，Orientation and geographicalloca−

tionoftheglacier．

5）Inaddition，dataforthevariationoftheglaciersin

the Bhutan Himalayas are collected onthebasis of

the toposheets（1：50，000scale publishedin thelate

1960s by the Survey ofIndia，grOund verifications

Carriedoutin196ト1963）andsatelliteimages（SPOT，
resolutionof20m，takeninDecember，1993）．Abase

mapoftheglacierboundariesin1963wasmadefrom
the toposheets．Glacier boundariesin1993 weremarkedonthesamebasemapfromacorresponding
SetOfsatelliteimages．Finallythesemapswereused

then

EエA＝CE＋AE−（月E十エE）／2，

Where EL，Ac：Approximated ELA from the relation
With CE and月E，ELAa：Approximated EL，A fromthe relation with AE and LE．

3．Glacierdistributionin the Himalayas
Fortheanalysisontheglacierdistributioninthe

Himalayas，dataofIndia，eaStNepalandBhutanare

to measure the variations ofterminiand areas ofthetaken from the glacier inventories by Geologicalthe glaciersin theIndian Himalayas by Geologicalfields，and glaciers with hanging andinterruptedininventory without explanation on the determination

tory were excluded．Glacierswith AAR of O orlOO
Which are seenin theIndianinventory were also
excludedfromthisanalysis．GlaciersinNepalwhose
lengthisshorterthan5kmwereexcludedforplotting

glaciersduringthe30yearsperiod（1963L1993）．Each Survey ofIndia（1999），by Asahi（1999）andICIMOD
glacierareawasmeasuredwithaplanimeter（Planix（2001），reSpeCtively．The whole Himalayan Rangeis
6，TamayaInc．）．Sinceitisdifficulttodistinguishthe dividedinto7regions（fromwesttoeast：Kashmir K ，activeterminiofdebris−COVeredglaciers，Onlydebris− HimachalPradesh H ，Gharwal G ，Nepal N ，Sik−
freeglacierswereselectedforthisanalysis．
kim S ，Bhutan B and ArunachalPradesh A ）asThe ELAis the mostimportant parameter toShownin Fig．2．The5regi0nseXCept Nepalandanalyzeglacierdistributionfromaviewpoint ofgla−
Bhutan belong toIndia．Listedglaciers with mor−
Ciermassbalance．However，theELAisnotgivenforphologicalclassificationsoftheglacierets andsnow−
SurveyofIndia（1999），andthealtitudeofthecontour theirlongitudinalprofile were excluded from thislinewhichdividestheaccumulationareainhalf（CE） analysis．RockglaciersarenotlistedintheIndianandandthatfortheablationarea（AE）aregiveninthe Bhutaneseinventories；thosein the Nepaleseinven−method ofthose．Therefore，the ELAwasestimatedusing the given CE and AE with the highest andlowestelevationsofeachglacier（月EandLE，reSpeC−
tively）．Method to calculate the ELA for theIndian

glacierswastakenasfollows．Supposing

inFigs．3and4，Sincetoomanyglaciersarelistedin

theinventoryforplottinginthenarrowspace．

nFig．2 Locationof7glacierizedreglOnSintheHimalayas．

32

Bu11etinofGlaciologicalResearch

ユJ．〟な／れ、5JのJd／（り廿ざ／（イ什〝タブりJJJ（り一〟けg山（、ん、JT

Distributionofthehighestandlowestelevations
Oftheglaciersinthe Himalayan Range alonglongi−
tudesisshowninFig．3atocomparethoseamongthe
regionsfromwesttoeast．Sincethehighestelevationof a glacier is controlled by the elevation of themountainrange，Only thosein the westernmost part

（Kashmir），Where the mountains are relativelylow
amongtheHimalayas，arelow．Thehighestelevations
OfglaciersinNepal，Wherehighmountainsexist，are

not so high，Since those correspond to the highest
elevationsofmainicebodieswhichareusuallylower
than the tops of the catchment areas in the glacierinventoryby Asahi（1999）．Thelowest elevations ofglaciers（altitudesoftheglaciertermini）arefoundto

belowerinthewesternandeasternpartsoftherange
thantheglaciersinthecentralpart．
Sincethelowestelevationoftheglacierisrather
representativefortheglacierregimethanthehighest

elevation，Fig．3b shows distribution of thelowest

elevations of the glaciers in the Himalayas along
latitudestocomparethoseamongregionsfromsouth

locatedatthehigherlatitudes．Ingeneral，risingofthe

ELAsfromnorthtosouthisseen，butariseofELAs

isnotsomuchfromtheregions H＆G to N，S，A
incomparisonwitharisefromtheregion K to H＆
G inFig．4b．Thistendencycanbe attributedto thepositiveeffectofthemonsoononmassbalanceinthe
easternHimalayasasseeninFig．4aandthelatitude

effectontheregion K asmentionedinthesection3．1．
ユ3．1匂γ由fわ乃qr娩gg由cわγねγ椚g乃猥

Theglaciersinthe NepalHimalayashavebeen

Shrinking considerablyinlength（terminus retreat），

area and thickness during the recent few decades（Higuchiet al．，1980；Fushimiand Ohata，1980；
Yamadaetal．，1992；Kadota etal．，1993；Fujitaetal．，
1997；Fujita etal．，2001；Kadota etal．，2002；Naito etal．，2002）．Variationsoftheglaciertermini（advancing，

retreatingorstationary）intheHimalayasareshown
inorderfromwesttoeastinTablel．Fortheglaciers
inthe5regionsinIndiaandinNepal，dataaretakenfrom GeologicalSurvey ofIndia（1999）and Asahi（1999），reSpeCtively．Alltypesofglaciersareincluded

tonorth．Generally，thelowerlatitudehasthehigher exceptglacierswithuncertaintongue activity．Since

airtemperatureatasame altitude andalsoreceives
the higher solar radiation．Such climatic condition
enables glaciers to distribute in the wider range oflowestelevations，increasingthehigherterminiatthe

the tongue activityis notgiven for the glaciersin

Bhutan by theICIMOD（2001），data of Bhutanin

Tablelrepresent onlylO3debris−free glaciers on
Whichtheglaciervariationismeasuredbythepresent
lowerlatitude as seenin Fig．3b．Thislatitudinal Study．The period for judging the tongue activity
differs from region to region．For theglaciersin
effect may allow the existence of glaciers with the
Nepaland Bhutan，those are from1959to1992andlowerterminiatthehigherlatitude（Fig．3b）whicharetheglaciersseeninthewesternmost mountainswith
from1963to1993，reSpeCtively．Theexactperiodfor
theglaciersinIndiacannotbeconfirmed，aSitisnot
thelowelevations（Fig．3a）．
Statedclearlyintheinventory．
AsseeninTablel，almostal1glaciersinIndiaand∴エ／：1〝J／／ん・山川／／柚 ′J／／／／J′′／lヾ・リー／／J・扉／′ノーハ
Bhutanandmostin Nepalhavebeenretreating and
Theequilibriumline altitude（ELA）is animpor−tantparameterformassbalanceofaglacier．Itrepre− advancedglaciersoccupynoneorsmallratiosineachregionintheHimalayanRange，thoughtheobserved
SentSregionalclimaticconditionintheglacierregime，
period and criteria of the judgment are different
Whilethehighestandlowestelevationsofglaciersare
amongcountries．
affectedadditionallybytopographicconditionofeach
glacier．Therefore，ELAis considered to reflect re−presentativelytheregionaldifferenceofthemonsoon
effect on the glacier regime over the Himalayan
Range．TheELAsofglaciersinIndiaandNepalwere
decided as mentionedin Section 2，and those of
Bhutanareexcludedduetolimiteddatainthepresent
analysIS．
DistributionoftheestimatedELAsoftheglaciers
intheHimalayanRangealonglongitudesisshownin

4．G（acier distribution and variationin the Bhutan

Himalayas

J．J‥Ⅵ†川ムりT／川〟川、（バ（！／一〃汀g〟汀JりT

TheInternationalCenterforIntegratedMountain
Developmentpublishedthemostdetailedinventoryof
glaciers and glaciallakesin the Bhutan Himalayas（ICIMOD，2001）．Thisinventorylisted677glaciersand
Fig．4a．Assameinthecase ofthelowest elevation， 2674glaciallakesin totalnumbers occupying1316．7
km2andlO6．8km2in totalareas，reSpeCtively．Gla−
glaciers show thelower ELAsin the eastern andCiersinthe BhutanHimalayasexistalongthenorth・
WeSternpartOftheHimalayasthanthecentralpart．
Moreoverglaciersinthewesternmostpart（Kashmir） ernborderadjoiningwiththeTibetanPlateau（Fig．5）．

withthesouthernaspectshowthehigherELAsthan
thosewiththenorthernaspect．
Figure 4b shows distribution of the estimated
ELAsin the Himalayas alonglatitudes．Glaciers atthelowerlatitudesshowthehigherELAsthanthose

Theicereservein Bhutanwascalculatedtobe127．25

km3in totalof eachglacier volume（ICIMOD，2001）

estimated from the empirical relation between the
areaandthethicknessofglaciersinTianshanMoun−tainsby LiuandDing（1986）．

ユヲ

Karma et al．

（a）

8 0 0 07 0 0 0

︵
∈
︶
u
O
軍
帽
＞
○
■
u

︵
○

0 0 0

5 0 0 0

▲
−

0 0 0

84

89

Longitude

︵
∈
︶
u
O
芋
空
r
O
■
0
1
∽
血
i
き
O
﹂

94

▲Highe＄t・Lowest︽ 0 0 0○5 0 0 0

0 00
4

27

28

29

30

31
Latitude

32

33

34

Fig．3 Distributionofthehighestandlowestelevationsofglaciersalonglongitudes（a）andthelowestelevationsofglaciersalonglatitudes（b）intheHimalayas．
NotationoftheregionsisglVenaSShowninFig．2．

35

36

34

BulletinofGlaciologicalResearch（a）

7 0 0 0

轟0 0 0○︵∈︶一
コ 5 0 0 0
u

▲0 0 0﹁84
Longitudeo No止h x＄outh

（bI

27

28

29

30

31

Latitude

32

33

34

35

o No止h x＄outh

Fig．4 Distributionoftheestimatedequilibriumlinealtitudes（ELAs）ofglaciersin
the Himalayasalonglongitudes（a）andlatitudes（b）．
NotationoftheregionsisglVenaSShowninFig．2．
Flowingorientationsofglaciersaredividedintonorthandsouth

36

35

Karma（ヲJαJ．

Tablel．Tongueactivityoftheglaciersinthe Himalayas，RegionKashmir
HimachalGharwalEastNepal
SikkimBhutan
Arunachal

Number of
glaciers

Retreat（％）

17
52
177
485
255
103
62

100．0
96．2
97．7
57．3
99．6
87．3
96．8

Stationary（％）

Advance（％）
0

1．9
2．3
34．9
0．4
12．7
3．2

0

1．9
0

7．8
0
0
0

Fig．5 GlacierdistributionmapoftheBhutanHimalayas（fromICIMOD，2001）．
Table2．Totalnumber，area and volume with average thickness ofeachglacier typein
Bhutan．（compiledfromICIMOD，2001）

Type

Valleyglacier
Mountaingl．
Iceapron
IcecapNiche
Cirqueglacier
Total

Number

51
453
94
16
51
12
677

Area（km2） Volume（km3） Thickness（m）
691．7690．222579．0235．510
33．40
1．197
5．19
0．182
5．57
0．105
1．79
0．035
1316．73
127．251

ThisinventorygroupedglaciersinBhutaninto6

130
61
36
35
19
20
97

Bhutan are analyzed in the same manner with thetypesandlistedtheirnumbers，areaSandicereserves

glaciersin the whole Himalayan Range．Likein thetype with the averaged glacier thickness that is
Obtainedfromeachtotalvolumedividedbyeachtotal
area arecompiledinTable2．Itcanbeseenthatthe
Valleyglacierhasthehighestvaluesofthetotalarea
andtheaveragethickness，thoughitsnumberis only
8％ofthe677glaciersinBhutanandthemajorityof
glaciersinBhutanbelongtothemountainglacier．

SnOWfield，andglacierswithhangingandinterrupted
intheirlongitudinalprofilewere excludedfrom thisanalysis．
Distributionofthehighestandlowestelevations

J．ヱ〃豆／Jぐ∫／J川（ブ／（りn−∫／tイ（，Ⅲ／／（川∫（モ「／／れ，g血（イlリT

highest elevations of glaciers distribute up to the（volumes）ineachofglacierized4basinsconsistedof previous case，1isted glaciersinICIMOD（2001）with
9sub−basins．Theirtotalsin Bhutanforeachglacier morphological classifications of the glacieret andThehighestandlowestelevationsof glaciersin

Ofglaciers alonglongitudesisshownin Fig．6．Thelowest elevations of allglaciersin the Bhutan

Himalayasarelocatedabove4000m．Sincethemoun−tainsarehigherinthewesternpart（from90．130E），the

higheraltitudes．Glaciersintheregionbetween90．230

36Bu11etinofGlaciologicalResearch

7 0 0 0

︵
∈
︶
u
O
焉
＞
○
■
山

0
良
V

00

5 0 0
0

90．O
Longitudo

90．5▲Highe＄t◆Lowe＄t

Fig．6 Distribution ofthehighest andlowest elevations ofglaciersin the Bhutan
Himalayasalonglongitudes．

E and90．840E showhigher terminialtitudes．Thisis easternmost regions favors such small glaciers to

due to the plateaulike topographyin this region
where the glaciers cannot flow down to the lower
altitudes，A group of smallmountain glacierswith

Verylowhighest（below5000m）andlowestelevations

arefoundtoexistintheeasternmostpart．Asimilar
SetOfglaciersisalsoseeninthe Bhramaputrabasin

distributeintheselowermountainreglOnS．
Large valley glaciers flowlng from very highpeaksintheHimalayasareusuallycoveredwiththickdebrisintheirlowerpart．Figure7showsthelowest
elevationsOf debris−COVered glaciers obtained from

GeologicalSurvey of Bhutan（1999）and those of（Arunachal）intheIndianHimalayas，theeasternmost debris−freeglaciersobtainedfromthepresentstudyin
theBhutanHimalayas．Clearlyitcanbeseenthatthe
part of the Himalayan Range（Fig．3a）．It can bethought that much monsoon precipitation in these

︵
∈
︶
u
O
芋
鴫
＞
○
−
●
l
笠
︳
石
﹂

lowest elevation of the debris−COVered glaciers are

0

0

0
甜
棚

0

▲

一
〇

OU

4

90．0
Lonがtudo

00．5
Odobri8・Ir00◆dobri8・｛OVOrOd

Fig．7 Distribution of thelowest elevations of debris−free glaciers and debris−
COVeredglaciersintheBhutanHimalayas．

91．0

37

Karma eial．

lowerthanthoseofthedebris−freeglaciers．Itcanbe Change，COmparisonoftheterminalvariationsamong
attributed to richice supply from thelarge upper
differentglaciersshouldbemadecarefully．Thecom−stream and insulating effect of ablation by thickdebrisofthedebris−COVeredglaciers．

4．ユ G血cわγねγ椚g犯∽〃αγぬメゐ乃カ℃桝J9氏ヲわj9玖ヲ

Ageta et al．（2000）examinedthe retreat rate ofparisonsaremadehereafterinthispaperfortheonly
debrisTfreeglaciers．Sincethisglaciergroupissmaller
in size（with thelength within severalkilometers），
COmparing to the debris−COVered glacier group，theaboveproblemisthoughttobereduced．

Selectedfourglacierswhichhaveglacierlakesattheirterminiby comparing photographs，Satelliteimages
andmapsindifferentyears．Themeanannualretreatsof the three glaciers among them in recent decades

glaciersfoundwithinthedatacollectedforthisanaly・duetoirregularcalvingoftheglaciertonguestotheirdescribedin Section2and the terminalaltitudesin

Wereinarangeof30−35minthehorizontaldistance．
However，therateswerevariablewithtime，prObably

InFig．8，terminalvariationsoftheglaciersinthe
BhutanHimalayasareshowninhorizontalandverti・

Calretreat alonglatitudes．There are no advancing

Sis．Since glacier boundariesin1993in the satellite
image were marked on the base mapin1963 as

lakes．In the present study，terminivariations of 1993were read at the contourlines of theglacierdebris−free glaciers are examined for a period of30 Surfacesin1963，theverticalretreatsareoverestimat−
years（1963−93），Sincethedebris−freeglaciersaremore
ed by the former glacier thickness at the terminal
SenSitivetotheclimatechange．Forthisanalysis，the positionsin1993．Adecreaslngtrendofglacierretreat
variousmaterialsareusedasdescribedinSection2．A
fromsouthtonorthcanberough1yseeninFig．8．

totaloflO3glaciersareincludedforthisanalysisfrom

different parts of the Bhutan Himalayas（Fig．5）．
Debris−COVeredglaciersareexcluded，Sinceitisdiffi−

Culttolocatetheiractiveterminuspositionunderthe
thick debris−COVer．

Sincethedistanceofterminalvariationisconsid−

ered to be controlled by the size of each glacier（Ageta，1995；Ageta et alリ2000）as wellas climate

Figure9shows the relation of annualretreat

rates averagedfor1963−1993inhorizontaland verti−

Caldistanceswiththelowestelevationoftheglaciersin the Bhutan Himalayas．Annualrates of glacier
Variationsinaveragesforthese30yearsdistributedina rangebetween a stationarystate and a horizontal
retreatof27myr￣1（8myr−1inaverticalretreat）．

一

；
−
■
卓
−
月
亡
O
H
℃
○

洞
⁝
m
⁝
加
二
刷

で
曾
亡
ご
；
−
葛
﹂
■
一
u
O
H
て
O
H

M
加
⁝
n 2丁．丁

2
2
1
1

−
︳

○

■
0

0

27．8

28．0

2丁．0

▲000 ●T00 4●00 ▲000 5000 t‖00 6200 め00 抑 8…

28．1

5

28．2

T●∩¶ln■l■l七山d●t叫

山川tudo
（b）

丁
亡
−
官
−

言
■
○
上
巳
−
さ
菅
■
＞

■

5
0

▲
9

一
己 一
一〇
8
モ
○
＞

一

帥

0
2

2丁．丁

2丁．8

28．0

2丁．0

2さ．1

28．2

L■dtud●Fig．8 Horizontalandverticalretreats ofthe debris−freeglacierterminiintheBhutanHimalayasalonglatitudes
for1963−1993．
Dashedlinesarethelinearregressionlines．

●l00 ●ア00

▲800

■800

さ000

5100

5200

8300

T●∩¶lml■仙●tt叫

Fig．9 Relationofannualretreatratesaveragedfor1963−1993in horizontaland verticaldistances with thelowest elevation of the debris−free glaciersin the
Bhutan Himalayas．

糾00

5500

BulletinofGlaciologicalResearch

こぼ／．J．（、．り〃／叶〃・∴ヾり〃J†・刷ぐん／−ゾけ／−ⅥJJ／〃〝ヾJ…●山／／りJJJJ／
凡函／．仙川ん抽J95抽／（＝，〝r（l・ノ！槻木

tabulatedin Table 3．The calculations were madeVariationsofthedebris−freeglacierterminiinthe
Bhutan Himalayas are comparedwith thosein theeast Nepal where detailed data are available fromfromtheratesofglaciersfordifferenttypesofvaria−

tionsi．e．for alltypes of variations（advancing，Sta−
tionaryandretreating），forstationaryandretreating

the former analyses．Here，data oflOO debris−freeonly andfor retreatingglaciers only；the rateswere
averagedfromtotalsofeach．glaciergroupasadvancT
ingtobenegativeandretreatingtobepositive．Inall
cases，aVerage Variation rates are higher for theglaciersintheBhutanHimalayas．

used．

・ノ．う．血…／用血血明 丹一 仙− g血（、かJ■（こrJぐ〃J／JJ／／れ−Asahi（1999）．For this analysis，the glacierets andsnowfields，andglacierswithhangingandinterrupted
intheirlongitudinalprofilewereexcludedassameas

glaciersinNepalfortheperiodfrom1959to1992are

Horizontalandverticalretreatsofglacierterminiin annualratesin the east Nepaland Bhutan
Himalayasareshownalonglongitudes andlatitudes

in Figs．10andll，reSpeCtively．Since there are noβゐ〟如乃〃才∽α吻′お力℃∽J9丘ヲわJ5悦ヲ

Arealshrinkage of glaciersin the Bhutan
Himalayasisevaluatedbythemethodasdescribedin

Section2．OutofthelO3debris・freeglaciersonwhich

advanclngglaciersinBhutan，theadvanclngglaciers

the terminivariations were analyzed，glaciers withincludedforthe comparisonpurpose．Periods ofthe
average rates for the glaciersin east Nepalandarealvariationwasmeasuredon66glaciersforthe30
yearsasshowninTable4．Theglaciershadatotal

intheeastNepal（12％oftheglaciernumber）arenot
Bhutan are33years（1959−1992）and30years（1963−93），reSpeCtively．Ageneralincreasingtrend ofthe

retreatratesfromwesttoeastcanberough1yseenin

the east Nepal（Fig．10）．Glaciersin both countries

Show a decreasing trend of the retreat rates from
SOuthtonorth（Fig．11）．

Averagevariationratesoftheglacierterminiin
theeastNepalandBhutanintherecentdecadesare

unclearlateralboundaries were excluded and thearea of146．87km2in1963andthe area decreased to134．94km2in1993；thatis8．1％shrinkage from thetotalareain1963．The percentage of shrinkage at
eachrangeoftheglacierareahasatendencythatthe
Smallerglaciershavethehighershrinkingratemore
thanthelagerglaciersasseeninTable4．Threesmall

glaciers（0．2，0．15，0．1km2in1963）completely

disappearedby1993．
㈲

三
言
︼
︶
一
審
■
2
■
8
u
O
H
t
O

2
2
1
一
7

■
0

一
〇

■
2
■
■0
■
■−

言
∫
−
− 〇
ご
疇
E
−
2
■ ︶
8
亡
O
H
t
○
O

8

0

86

80

1丁

−

盲
ぞ
旦
；
宏
五
重
■
■
○
モ
○
＞

88

Lon伸一●

89

00

如h血nl

01

27．0

2丁．丁

2丁．8

2丁．0

2tI．0

畑山do

L画
28．1

28．2

28．ユ

28．1

28．2

28．3

T
︵
L l
盲
︶ 一
書〇
■
℡
モ ▲
モ﹁
r

T
1
5
▲
﹁

t
Y

t
V
2

■
Y

2

86

80

0丁

88

●l

00

Lo叩仙d0 o＝●叫▲些些吐01

Fig．10 Horizontalandverticalretreatsofdebris．freegla−cierterminiinaveragedannualratesintheeastNepal（1959−1992）and Bhutan Himalayas（19631993）along
longitudes．

2丁．0

2丁．丁

2丁．8

2丁．9
M仙do

2l．0

叫

Fig．11Horizontalandverticalretreatsofdebris−freegla−cierterminiinaveragedannualratesintheeastNepal（1959−1992）and Bhutan Himalayas（1963−1993）along

latitudes．

Karma et al．

3ご）

Table3．Average variation rates of glacier terminiin east Nepaland Bhutanin the recent
decades．
Forretreating（positiverate），Stationaryandadvancing（negativerate）graciers
RegionPeriod（years）
Variationrate（m／yr）
No．ofglaciers
VerticalHorizontal
Nepal
33（1959−92）
0．59
3．14
100
Bhutan30（1963−93）
1．9
6．27
103

Forretreatingandstationaryglaciersonly
Bhutan33（1959−92）30（1963−93）

Forretreatingglaciersonly
Bhutan33（1959−92）30（1963−93）

Table4．Arealshrinkage from1963to1993for the different size of glaciersin the Bhutan
Himalayas．
Areain1963

Number Totalarea Totalarea Totalareaofin1963
in1993（km2）
glaciers
（km2）
（km2）
01
22
11．11
8．64
12
14
19．36
16．61
2−3
12
28．68
25．98
3−4
27．98
26．27
4−5
12．62
11．89
5−6
16．32
15．43
8−12
30．8
30．12
TOTAI」
66
146．87134．94Noglacierintheareaof6−8km2in1963．
9
3
3
3

shrank
（km2）

2．47
2．75
2．7
1．71
0．73
0．89
0．68
11．93

Shrinkage
（％）

22．2
14．2
9．4
6．1
5．8
5．5
2．2
8．1

5．Discussions and conclusions

こ了．ユ（ごんJ（、んり一川ノ五J／／りJJナナJ仙、〃／〃〟巾l・俗

5．ノ．（；血（・〆り・rJふ／J蕗J′晶JJJJJ〟げ〃わJJ〝んり・（びing areas have characteristics of being a summer・
accumulation type ．Theglaciers receive most of

Monsoonprecipitationincreasestowardtheeast−

Theglaciersinthe Himalayasandthesurround−ern（southern）partfromthewestern（northern）partin
annualaccumulationinsummerwhenablationoccurs
theHimalayanRange（e．g．Eguchi，1994，Fig．1）．The
Simultaneously．The higher summer air temperature

higher precipitation increases glacier accumulationand decreases ablation due to accompanied cloudy

Weather．In relation with the above，the following

tendencies of glacier distribution were found in thepresentstudy．

・Thelowestelevations（Fig．3a）andtheELAs（Fig．

4a）of the glaciersin the eastern half of theHimalayas descend towardeast from Nepalvia

Sikkim−Bhutan to Arunachal）which arelocatedat the similarlatitudes．

・The ELAsin Fig．4binNepal・Sikkim−Bhutan−
Arunachal（south）arenotsomuchdifferentfrom

providesthe following negative effects on massbal−
ance of summer−aCCumulation type glaciers（Ageta
andHighuchi，1984；AgetaandKadota，1992）．
1）Increasedproportionofraininthetotalprecipita−

tionreducesaccumulationbysnowfall．
2）Decreased albedo due toless snowfa11enhances
ablationbyinsolation．
3）Highertemperatureincreasesablation．

Asaresult，glaciervariationinthemonsoonarea
dependssensitivelyonthesummerairtemperatureas
Shownwith empiricalrelations of accumulation andablationwithprecipitationandairtemperaturebythe

thoseinHimachal＆Gharwalatthehigherlati− above references．The above characteristics are also
tudes，thoughthoseinthewesternhigherlatitudes

ShownwiththesimulationmodelbyFujitaandAgeta

toward north due to thelatitude effect．

modelincludingalbedoeffectandothers，andwiththe

descend from Himachal＆Gharwalto Kashmir

・Groupsofsmallmountainglacierswithverylow（2000）which consists of the detailed energy balance

SimulationmodelbyNaitoetal．（2001）whichincludes
glacierdynamics．Onthebasisoftheempiricalequa−
easternmostpartsofBhutanandArunachal（Figs． tioninAgeta andKadota（1992），maSSbalancevaria−
highest andlowest elevations were foundin the
3a and6）．

These tendencies of glacier distribution are

attributedtothemonsooneffectduetothecharacter−isticdistributionofprecipitationmentionedabove．

tionofaglacierincaseofsametemperatureincrease
andconstantprecipitationisexpectedasfollows．
1）Decrease ofaccumulationismoreinan area withhigher precipitation（east／south），Since accumulation

40

isproportionalto precipitation under the same tem−
peraturecondition．
2）Increase ofablationismuchmore at the warmer

Report 2（1994−1998），Institute for Hydrospheric−AtmosphericSciences，Nagoya University；Departmentof
Hydrology andMeteorology，HMGofNepal，1r76．
Eguchi，T．（1994）：Regionaldifferencesinprecipitationandthe
place（lowerlatitudes，loweraltitudes），Sinceablation
CaSueOfdryvalleysintheBhutanHimalaya．In：Regional
isapowerfunctionofairtemperature．
differencesin precipitationin the globe，theIndochina
Peninsula and the Bhutan Himalaya（176pp）．Doctoral
Almost all glaciers measured in the wholethesis，Graduate
Schoolof Science，the University of
Himalayashavebeenretreatingintherecentdecades
Tokyo，111−167．
（Tablel）．InBhutan，tOtalarealshrinkagefrom1963
Fujita，K．andAgeta，Y．（2000）：Effectofsummeraccumulation
to1993for66debris・freeglaciersis8％oftheinitial
Onglaciermassbalance onthe Tibetan Plateau revealed
total（147km2）and the shrinkage rates of smallerbymass−balancemodel．J．Glaciology，46，244▼252．
Fujita，K．，Kadota，T．，Rana，B．，Kayastha，RB．andAgeta，glaciers arehigher than those of thelarger glaciers（2001）：Shrinkage of Glacier AXOlOin Shorong region，（Table4）．Andthefollowingdifferencesinvariationof
NepalHimalayasin the1990s．Bulletin of Glaciologicaldebris−freeglacierswerefound．
Research，18，51L54．
・RegionaldifferencesofglacierretreatwerefoundFujita，K．，Nakawo，M．，Fujii，Y．and Paudyal，P．（1997）
between Nepaland Bhutan；the average retreat
ChangesinglaciersinHiddenvalley，MukutHimal，Nepal
Himalayas，from1974to1994．）．Glaciology，43，583588．
ratein Bhutan（east from Nepal）is higher than
Fushimi，H．andOhata，T．（1980）：Fluctuationsofglaciersfrom
Nepa‖ntherecentabout30years（Table3）．
1970to1978intheKhumbuHimal，EastNepal．Seppyo，41，
・Somezonaldifferenceswererough1yseensuchas
Specialissue，71−81．
increasingtrend ofglacier retreat from west to
Gansser，A．（1970）：Lunana．The peaks，glaciers andlakes of
eastinNepal（Fig．10），from north to southin
northern Bhutan．The Mountain World1968／69，Swiss
FoundationforAlpineResearch，117131．
Nepal（Fig．11）andinBhutan（Figs．8andll）．
GeologicalSurveyofBhutan（1999）：Glaciersandglacierlakes
These regionaland zonaltendencies of glacierinBhutan．83pp．
variationcanbeattributedtothemassbalanceeffectGeologicalSurveyofIndia（1999）：InventoryoftheHimalayan
mentioned above．
glaciers．AcontributiontotheInternationalHydrologicalAs the result described above，Characteristicsin
Programme，SpecialPubl．no．340fGSI，165pp．
Higuchi，K．，Fushimi，HリOhata，T．，Takenaka，S．，Iwata，
thedistributionandvariation of Himalayanglaciers
Yokoyama，K．，Higuchi，H．，Nagoshi，A．andIozawa，T．
have been understoodin term oflocaldifference of（1980）：Glacierinventoryin the Dudh Kosiregion，Eastmonsoon activity and the mass balance feature of
Nepal．Proceedings of the Riederalp Workshop，1978；
Summer−aCCumulationtypeglaciers．
WorldGlacierInventory，IAHS−AISHPubl．no．126，95rlO3．
International Center for Integrated Mountain Development（2001）：Inventoryofglaciers，glaciallakesandglaciallake
Acknowledgments
Outburstfloods−Bhutan．227pp．
Kadota，T．，Naito，N．and Conway，H．（2002）：Someshrinking
We areindebtedto Dr．P，K．Mool，ICIMOD andfeaturesin the uppermost ablation area of the Khumbu
Mr．K Asahi，Hokkaido University for providing
Glacier，eaSt Nepal，19951999．Bulletin of Glaciologicaltheirdigitalinventorydata，andalsotoDr．M．Nak・
Research，19，37▼40．
Kadota，TリSeko，K．andAgeta，Y．（1993）：ShrinkageofGlacierawo，Dr．K．Fujita，Dr．A．Sakaiand Mr．F．Nakaz・
AXOlOsince1978，ShorongHimal，EastNepal．Proceedings
awa，formerInstitute for Hydrospheric−Atmospheric
Of the Kathmandu Symposium，1992；Snow and Glacier
Sciences，Nagoya Universityfor theirvaluablecom−
Hydrology，IAHSPubl．no．218，145−154．
ments，SuggeStionsandsupportsduringthisstudy．
Liu，C．and Ding，L．（1986）：The newly progress ofglacierinventoryin Tianshan Mountains．）．Glaciology andGeo−
CryOlogy，8，168−169．
References
Naito，N．，Ageta，YりNakawo，M．，Waddington，E．DリRaymond
C．F．and Conway，H．（2001）：Response sensitivities of a
Ageta，Y．（1995）：RecentglacierfluctuationsintheinlandAsia
Summer−aCCumulationtypeglacierto climate changesin−（inJapanese）．Seppyo，57，35−40．
dicated with a glacier fluctuation model．Bulletin of
Ageta，Y．and Higuchi，K．（1984）：Estimation of massbalance
GlaciologicalResearch，18，1−8．
COmpOnentSOfasummer−aCCumulationtypeglacierinthe
Naito，N．，Kadota，T．，Fujita，K．，Sakai，A．and Nakawo，
NepalHimalaya．GeografiskaAnnaler，66A，249−255．
（2002）：Surfacelowering overthe ablation area of Lirung
Ageta，Y．，lwata，S．，Yabuki，H．，Naito，N．，Sakai，A．，Narama，Glacier，NepalHimalayas．Bulletin of GlaciologicalC．andKarma（2000）：Expansionofglacierlakesinrecent
Research，19，41「46．
decadesin the Bhutan Himalayas．Proceedings of the
UNESCO／IASH（1970）：Perennialice and snow masses．A
SeattleWorkshop，2000；Debris−Covered Glaciers．IAHS，
COntribution to theInternationalHydrologicalDecade，Publ．no．264，165−175．
59pp．
Ageta，Y．and Kadota，T．（1992）：Predictions of changes of
Yamada，T．，Shiraiwa，T．，Iida，H．，Kadota，T．，Wa
glaciermassbaZanceintheNepalHimalaya and Tibetan
Rana，B．，Ageta，Y．andFushimi，H．（1992）：Fluctuationsof
Plateau：aCaSeStudyofairtemperatureincreaseforthreetheglaciersfromthe1970sto1989intheKhumbu，Shorong
glaciers．AnnalsofGlaciology，16，89−94．
and Langtangregions，NepalHimalayas．Bulletin ofGla−
Asahi，K．（1999）：Data oninventoriedglaciersanditsdistribu−
CierResearch，10，1ト19．
tionin eastern part of NepalHimalaya．CREH Data