Bu11etinofGlaciologicalResearch20（2003）7−14

7⑥JapaneseSocietyofSnowandIce

Positive degree‑day factors for ice ablation on four glaciers in the Nepalese Himalayas andQinghai・Tibetan PJateau

RijanBhaktaKAYASTHAl，YutakaAGETAl，MasayoshiNAKAWO2，KojiFUJITAl，AkikoSAK

Yoshihiro MATSUDAllGraduateSchoolofEnvironmentalStudies，NagoyaUniversity，Nagoya464−8601Japan

2ResearchInstituteforHumanityandNature，Kyoto6020878Japan（ReceivedAugust9，2002；Revisedmanuscriptreceived November26，2002）

Abstract

PositivedegreeTdayfactorsforiceablationonYalaGlacier，CentralNepal，Xiao Dongkemadi
Glacier andJulylst Glacierin the Qinghai−Tibetan Plateau，WeSt China，are Calculated during a
Summer SeaSOn Of1996，1993and2002，reSpeCtively，and comparedwith the degree−day factors
CalculatedonGlacierAXOlO，eaStNepalduringasummerseasonof1978．Thedegree−dayfactorsfor
Summericeablationattwoaltitudes5120mand5270ma．s．l．onYalaGlacierrangefrom8．OtolO．5
mmd￣lOC」．InthecaseofXiaoDongkemadiGlacier，thefactorsrangefrom13．3（at5425m）to14．2
mmd▲loC￣1（at5475m）andonJulylstGlacier，thefactorsataltitudesfrom4305mto4619ma．s．1．
rangefrom5．5to8．8mmd￣10C．1．Largerdegree−dayfactorsarefoundonglacierssituatedathigher
altitude・Theresultsoftheindividualglaciersalsoindicatethatthedegree・dayfactorforiceathigher

altitudeislargerthanattheloweraltitude，Whichismainlydueto ablationattributedto absorbed

globalradiationatthehighaltitudewherethepositivedegree・daysumislowduetolowsummerairtemperature．

1．lntroduction

The most important energy source for glacierablationintheHimalayasisradiation．Manystudies
haveshownthatnetradiationisthedominantenergy
source for ablation．The net radiation contributes

morethan80％ofthetotalenergysupplyforablation

intheNepaleseHimalayas（OhataandHiguchi，1980；
Kayastha et al 1999；Kayastha，2001）．

Air temperatureis animportant meteorologicalelementforexplainingvariationsinablationandmass

radiation，theincominglongwaveradiationisimpor・

tantcomponentofincomingheat sourcefor melt at

Surface，Which transferinformation of air tempera−
tureto surface（Ohmura，2001）．Hefoundthat under
Clearsky，about60％ofthe atmosphericemissionis

derivedfromwithinthefirstlOOmand90％fromthe

firstlkmoftheatmosphere．Whentheskyisover−

CaStWiththecloudbottomwithinthefirstlkm，mOre
than90％originates within thislayer between thesurface and the bottom of the cloud．

Thedegree−dayconceptwasappliedinglaciology

balanceofaglacier．Inparticular，themeltingofsnow forthefirsttimebyFinsterwalderandSchunk（1887）

Oriceduringanyparticularperiodisassumedtobe
proportionalto the sum ofdaily mean temperatures
above the melting point during that period and theintheAlpsandhasbeenusedsincebymanyauthors．

factorlinkingablationtothistemperaturesumistheing over the whole Greenlandice sheet，and usedin

invoIves a simplification of complex processes thatare properly described bythe energy balance ofthe
glaciersurfaceandoverlaylngatmOSphericboundary
layer．Thisisbecausethefactorsdeterminingthemelt
process are correlatedwith temperature orin other
WOrds，the airtemperaturecontainstheinformation

Severalmodelsandempiricalrelationshavebeen
proposedtocalculateglacierablationintheNepalese

BraithwaiteandOlesen（1985；1989），andBraithwaite（1995a）usedthedegree−dayconceptunderGreenland
Sumiscalledthepositivedegree・daysum（PDD）．The COnditions，mOdifiedbyReeh（1991）tocalculatemeltT
positive degree−day factor．The degree−day factor

ice−dynamics modelling by Huybrechts et al．（1991）
andLetreguillyet al．（1991）．Similarly，Laumannand
Reeh（1993）andJohannesson et al．（1995）used thedegree，daymethodforestimatingmeltratesondiffer−entglaciersinIceland，NorwayandGreenland．

Of a major energy source．For example，inthe net Himalayas，forexample，empiricalrelationstocalcu−

βBulletinofGlaciologicalResearch

1ate glacier ablation by Ageta and Higuchi（1984），

ablationareaonicesurfaceratherthansnowsurface．

simplified models for estimating glacier ablation

Andthedegree−dayfactorforiceablationisalso an

for glacier mass balance on Glacier AXOlO by

main purpose of the present paper is to find out

The ablation area of many glaciers in the
Himalayasiscoveredwithdebris．Debrishasastrong
influenceonthesurfaceenergybalanceandmeltingof

areobtainedandcomparedwithGlacierAXOlO，eaStunderdebrislayerby NakawoandTakahashi（1982） importantparametertoestimateicemeltingundera
debrislayer（Kayastha et al．，2000b）．Therefore，theandRana et al．（1997），andenergybalancemodelling
Kayasthaetal．（1999）．

applicable degree−day factors forice on debris−freeglaciers．ThefactorsonYalaGlacier，CentralNepal，ⅩiaoDongkemadiandJulylstGlaciers，WeSt China，

theunderlyingice．Thethermalconductivity（orther−

Nepal（Kayastha et alリ2000a）to study the spatial
Variationofdegree−dayfactoranditscauses．

conductiontotheice−debrisinterface．Kayasthaetal．
（2000b）studiedthepracticalpredictionoficemelting

2．Studied glaciersanddata

Glacier，Nepal，uSingadegree−dayfactor．Degree−day

Fig．1．

were found and a practical relationship between

2．J．i匂ゎCんzcブβれCe乃わⅥJJⅥ少αJ

malresistance）and albedo are the main physicalcharacteristics of a debrislayer that controlheat
beneathvariousthicknessofdebrislayeronKhumbu
factors for ablation under various debris thickness

debris properties and degree−day factor was estab−

1ished for estimating ablation under a debrislayer．
The data required to predict ice ablation under adebrislayeraredegree・dayfactorforiceablation，air

temperature andrelationbetweendegree−day factor
andthermalpropertiesofdebrislayer．
There are useful correlations between ablation

Locations of studied four glaciers are shown in

Yala Glacierin Langtang Valleyis one of themostinvestigatedglaciersintheNepaleseHimalayas．
Thehighestandlowestaltitudesare5749mand5094

ma．s．1．，reSpeCtively，andtheareaoftheglacieris2．5
k1112．

Datacollectedduringtheglaciologicalandmete・

OrOlogicalobservationsonYalaGlacierfromJunetoand air temperature，Which are very convenient toapply on glaciers in remote areas where detailed

present study．The observed mean air temperature

daymethodisusedtoestimatebasindischargefrom
two glacierized basins in the Langtang Valley

above period．Among eight stakesinstalled andObservationsarescarce．Inthisregard，Simpledegree−

Septemberin1996（Fujita etal．，1998）areusedinthe
WaSl．60Cat5350ma．s．1．andtotalprecipitationwas
753mmattheglaciercamp（5110ma．s．1．）duringthe

maintained at different altitudes to obtain the mass
（Kayastha et alリ2003）and the results arein goodbalance oftheglacier duringthe monsoon seasoninagreement with observedvalues．To use the degree−
daymethod，thedegree−dayfactorisakeyparameter． 1996，Onlydataattwostakesatthelowerpartofthe
Generally，thefactorsforsnowandiceablationsare
glacier（5120mand5270ma．s．1．）areusedtoanalyse
icemeltinthisstudy．However，thesmallamountof
different；thefactorforiceablationislargerthanfor
snow ablation due to thelowerice albedo（Braith−
SnOWfa11broughtbysummermonsoonisalsoincluded
waite，1995a）．Glacier ablation mainly occursin the in theicemelt amount（Tablel）．Verylowicemeユt

Fig．1．Locationmapofstudyarea．Thenumbersl，2，3and4represent
GlacierAXOlO，YalaGlacier，ⅩiaoI）ongkemadiGlacierandJulylst
Glacier，reSpeCtively．

Kayastha et al．

OCCurredatstakesathigheraltitude．

9

SumOfablationestimatedfromicesurfacelowering

glaciercamplSaSSumedthesameatthetwostakesof
presentstudy．Itisassumedthat allsnowfallduring
theperiodwasmeltedoutattheend．Airtemperature

amount ofsolidprecipitationiscalculatedusingthe
relationbetweenprobabilityofsolidprecipitationand

rateof5．50Ckm▼1（Fujitaetal 1997）isusedtoderive

The totalamount of ablationis calculated as aand the melting of solid precipitation（snow）．The

air temperature obtained by Ageta et al．（1980）onGlacier AXOlO．The precipitation observed at the

WaSreCOrdedinadataloggerataltitude5350ma．s．1．，

anditsdailymeanvaluesareusedforPDD．Thelapse

thetemperatureatlowerelevations．

Tablel．Calculatedmonthlydegree−dayfactors（k）foriceandrelatedparametersona）Yala
Glacier，b）ⅩiaoDongkemadiGlacierandc）JulylstGlacier．Valuesinparenthesesshow
theiceandsnowablations，reSpeCtively，OnYalaandJulylstGlaciers．Seasonalvalues
OfablationandPDDarecumulativetotals；theseasonaldegree−dayfactorsarecalculated
from these totals．
a）YalaGlacieri）Stakeat5120ma．s．1．
Ablation
Months（mmw．e．）

June
July
AugustSeptember
Seasona1

768（731＋37）

897（844＋53）

711（557＋154）
493（435＋58）

2869（2567十302）ii）Stake at5270m a．s．1．

June
July
August＊September
Seasonal

518（468＋50）
901（816＋85）298（94＋204）◆

462（400＋62）

1881（1684＋197）

PDD

k

76．5
104．7
117．4
61．3
359．9

（mmdJIQC−1）
10．0
8．6
6．1
8．0
8．0

57．4
80．3

9．0
11．2

（OCd）

93．0♯

42．2
179．9

・0mittedinFig．2andincalculationforseasonalvalues．

3．2■

10．9
10．5

b）XiaoDongkemadiGlacieri）Stakeat5425ma．s．1．
MonthsJuly

AugustSeasonal

Ablation（mmw．e．）
661
657
1318

ii）Stakeat5475ma．s．1．
July
AugustSeasonal

535
611
l146

PDD

k

47．8
51．0
98．8

（mmd￣10C▼1）
13．8
12．9
13．3

38．7
42．2
80．9

13．8
14．5
14．2

（OCd）

C）JuIylstGlacieri）Stakeat4305ma．s．1．
MonthsJuly
AugustSeasonal＋＋

Ablation（mmw．e．）919（873十46）662（630＋32）
1945（1809＋136）ii）Stake at4483m a．s．1．
lOO5（918十87）
July
August552（495＋57）
Seasonal＝1849（1620＋229）iii）Stakeat4619ma．s．1．

PDD
（OCd）

151．8
134．0
353．8

107、0

92．7
255．7

k

（mmdLlOC￣l）
6．1
4．9
5．5

9．4
6．0
7．2

683（531十152）
73．7
July
9．3
August589（522＋67）
63．1
9．3
Seasonal＝1473（1152＋321）
167．2
8．8
＊＊theseseasonalvaluesarecumulativetotalsfrom150r16Juneto4Sept．2002．

JO

BulletinofGlaciologicalResearch

2．2．見抜卜仇明が捌那成1識狛如∵附加C血玩焔

ⅩiaoDongkemadiGlacierliesirlthemiddユeofthe
Tanggula Mountains（330N，92OE），CentralQinghai−
TibetanPlateau，WeStChina．Thehighestandlowest

elevationsoftheglacierin1993were5926mand5380

assumedtobe900kgm−3andthatofsnowexistedatthebegirmingofobservation，basedonmeasurements，
is450kgm￣3．Thethresholddailymeanairtempera−

turebetweensnowfallandrainfallisassumedtobe3．7

OCbasedontheresultsobtainedatthemeteorological

StationonYangLong HeGlacier，QilianMountains，
ma．s．1．，reSpeCtively，thelengthwas2．8km，andthe
China（DingandKang，1985）．Altitudinaldependence
areawasl．77km2．Theglaciersurfacefacessouthto

southwestwithagentleslope．
Measuredairtemperatureandsimulatediceabla−

Ofprecipitationisneglectedduetolackofdata．

dayfactorsforicearecalculatedataltitudesof5425

Nepalese HimalayasinShorong Himal．Thehighest
andlowestelevationsontheglacierin1978were5360

tionbyamassbalancemodel（FujitaandAgeta，2000）
inJulyandAugust1993areusedinthisstudy．Degree・
m and5475m a．s．1．，Where surface composition was

dominantlyiceduringthestudyperiod．Theobserved

2．4．G由仁gβγA見りJq eがJ〃勿αJ
Glacier AXOlO lies at the southern front of theand4950m a．s．1．，reSpeCtively，thelength along theCentrelinewasl．7km，andtheareawasO．57km2．Themeanairtemperaturewas−0．lOCat5600ma．s．1．andglacierendsatapond．Thealtitudeofthemeteorolog−
totalprecipitationwas339．5mmattheglaciercamp
icalobservationsitenearthebasecampwas4958m（5500m a．s．1．）during the period．The mass balancea．s．1．，Wheremeteorologicaldatawererecorded．The
modelby Fujita and Ageta（2000）calculates glacierablationusinganenergybalanceattheglaciersurface
incorporating the process of water refreezing．The

results of the model verification showed that themodelwasindeedrepresentativeofthesurfacecondi−

tions，heat balance，heat conductionin the glacier，mass balance and refreezing process at different
glacieraltitudes．
∵．．●∴ノ／小ト／lJ山・ノー／、／い／（ソ高J・J

Observedmean air temperaturewas2．7OC and total
precipitation1236mmatthemeteorologicalobserva−
tionsiteonGlacierAXOlOfromJunetoAugust1978．
Measuredairtemperatureandiceablationsimulated

by a glacier mass balance model（Kayastha et al．，
1999）areusedinthisstudy．
3．Degree・dayfactors

By definition，degree−dayfactor，kis calculated
JulylstGlacierisanorth・facingglacier，locatedonQilianMountainsinthe Qinghai−Tibetan Plateau， asaratiooftotalablationduringacertainperiodto
thePDDinthesameperiod（k＝tOtalablation／PDD）．
west China（39015 N，97045 E）．Meteorological，In general，the effectiveness of degree−day factor
hydrologicalandglaciologicalobservationswerecar−

ried out by a joint research team of Japanese andChinese scientists on this glacier from mid June toearly Septemberin 2002．The highest andlowest
elevationsontheglaciermeasuredbyGPS are5088

dependsonthedegreeofconsistencyofablationand

airtemperature．Therefore，Cumulativemonthlyabla−
tionversusPDDonYala，ⅩiaoDongkemadiandJuly
lst Glaciers are plottedin Fig．2．The datainJuneand4295m a．s．1．，reSpeCtively．Thelength along COntainsonly150r16daysandthedataof4daysin
thecentrelinein1985was3．8km，and thearea was2．98
km2（Liuetal．，1985）．Thealtitudeofthemeteorologi−
calobservationsitewas4291ma．s．1．，Wheremeteoro−

logicaldatawerecollectedfromllJuneto4Septem−

ber2002．Theobservedmeanairtemperaturewas4．4 ︵．

DCandtotalprecipitation250mmatthemeteorologi−
calobservationsiteduringtheobservationperiod．
Amongthe28stakesestablishedontheglacierto
monitor the glacier mass balance，ablation at only
threestakesataltitudesof4305m，4483mand4619m

a．s．1．are consideredin the present study．Snowmelt

was dominated above the altitude4619m a．s．1．Air

〇
．
き
且
弓
焉
l
焉
ぎ
焉
∃
∈
n
U

2
つ
一
l

5

0

5

十Y血（5120m）」卜Y血（5270m）＋XlaO（5425m）

︵
U

■
1

5

一8一Ⅹiao（5475m）

一一rJdylst（4305m）

0temperaturewasalsomeasuredatthealtitude4619m

a．s．l．，andlapserate ofairtemperaturebetweenthe
meteorologicalobservationstationandat4619ma．s．1．
was8．lOCkm￣1．Thislapserateisusedtogettheair

temperatureathigheraltitudesthanthemeteorologi−
calobservation station．Almost allsnowfallat threestakesduringtheobservationperiodwasmeltedout
attheend．Thetotalamountofablationiscalculatedsame as on Yala Glacier．The density oficeis

一○一J山ylst（44裳3m）−★J山ylst（4619m）

0

50 1（氾 150 200 250 300 350 400
CumuhtivePDD（Ocd）

Fig．2．Cumulative monthly ablation versus cumulative
monthlyPDDorlYala，XiaoDongkemadiarldJulylst
Glaciers at different altitudes．DatainJune on Xiao
DongkemadiGlacierwhensnowablationwasdominant
isincludedinthisfigure．

Kayastha et al．

ノブ

SeptemberisincludedinAugust onJulylstGlacier．
Althoughthelinesarenotperfectlystraight，thereis
ahighdegreeofconsistencybetweenablationandair

August were relatively smalland changelittle with

formonthlyandseasonalablationsareobtainedfrom
totalablationandPDDduringtheconcernedperiod．

mer monsoon activity is strong and cloud amountincreasesinJulyandAugust（monthlyaveragedclouda．s．1．）onGlacierAXOlOin1978（Fig．10inKayasthaetal．，2000a）．The degree−day factors forJuly andtemperatureontheseglaciers．Thedegree・dayfactors respecttoaltitudecomparedforJune．Sincethesum−
However，at an altitude of5270 m a．s．1．on Yala
Glacier，Onlythreemonths（June，JulyandSeptember）
totalvalues are usedfor seasonalablation as wellasamountin tenthsin daytime：June8．7，July9．7，and
August 9．6），glacier ablation was reduced due todecrease ofincomingglobalradiation．However，theユム】高山．Y由りβり〃gかJ〃〝（′′（川（ノノJ′（l一九′〔油（イ（−JT

dayfactorincreaseswith respect to altitude andits

month1yablationduetomostlysnowmeltoccurrenceinAugust．
Calculateddegree−dayfactorswithotherrelatedparameters on Yala，Xiao DongkemadiandJulylst
GlaciersareshowninTablel．Monthlyandseasonal

degree−dayfactorswerelargeinJuneduetoablation
bylarge amount of absorbed globalradiation（Kayasthaetal．，2000a）．Theseasonalaveragedegree−

Valuerangesfrom7．7toll．6mmd▲lOC〜1．Averaged
degree−dayfactorsatsevenpointsforseasonalabla−tion on Glacier AXOlO was 9．3 mm dJJIoC．1．Thedegree−dayfactorsonYalaGlacierrangefrom6．1toCalculatedaveragedegree−dayfactorforicefromLlO
ll．2and from8．O tolO．5mm dJlOC1，reSpeCtively；
toLlOO（5145ma．s．1．）was8．7mmd￣lOC￣1，duringthe
thoseonXiao DongkemadiGlacierfrom12．9to14．5 iceablationperiodfromJunetoAugust1978（Fig．2in
andfrom13．3to14．2mmd▼loCrl，reSpeCtively．Simi−
Kayastha et al．，2000a）．
1arly，mOnthlyandseasonaldegree−dayfactorsonJuly
lstGlacierrangefrom4．9to9．4andfrom5．5to8．8
4．Comparison ofdegree・dayfactors
mmd▼loC￣1，reSpeCtively．Averagedseasonaldegree−
dayfactorsforiceatdifferentaltitudesonYala，Ⅹiao
Calculatedseasonaldegree−dayfactorsforiceon
DongkemadiandJulylstGlaciersare9．3，13．8and7．2
GlacierAXOlO，Yala，ⅩiaoDongkemadiandJulylst
mm duloC1，reSpeCtively．The monthly degree・day GlaciersareplottedinFig．4．Ingeneral，thedegree−
factors forice at different altitudes of Yala，Ⅹiao
dayfactorforiceincreasesasaltitudeincreasesand

DongkemadiandJulylst Glaciers are plottedin

Fig．3．In general，the degree−day factor at higher

altitudeislarger than atlower altitude．Ablation

thistrendholdswithinaglacieraswellasincompari−
SOnbetweentwoormoreglaciersofdifferentregions．
Duringthemainablationperiod／zonewithhighPDD

aroundOOC（withsmallPDD）ismainlyattributedtoValues on Glacier AXOlO，degree−day factors forice

the absorbed globalradiation，Which has dominant
effect onhavingalarge degree−day factor at higher

Showedrelativelysimilarvaluesatdifferentaltitudes．

altitudesthanatloweraltitudes，Called thelowtem−
peratureeffect （Braithwaite，1995a）．

︵
一
・
の
・
d
一
ヒ
︶
￠
p
3
や
召

．
∽
d
∈
︶
○
召
−
空
く

20
0
0
0
8
0

5
4

O

0
0

O〇
一

一U
U

0

5
50
4

5

4

（i

g lO

12

14

1（i

Degree−dayfhctor（mmd￣loc■1）

Fig．3．Altitudeversusmonthlydegree−dayfactorsforice1015

恥卵8−d町如or（md−10c・1）

Fig．4．Altitudeversusseasonaldegree−dayfactorsforice
OnGlacierAXOlO，Yala，XiaoDongkemadiandJulylst

Glaciers．Solidlinesrepresentregressionlines．

On Yala，Ⅹiao DongkemadiandJulylst Glaciersin
1996，1993and2002，reSpeCtively．

ユ2．G／αCグgγAズりJO

Monthly（June，July and August）and seasonal（June to August）degreeTday factors were calculated
atsevenpointsfromLlO（4956ma．s．1．）toU30（5245m

Degree−day factors for snow andice at various

locationsastabulatedinBraithwaiteandZhang（2000）
andKayasthaetal．（2000a）areshownwiththeresults

Of present studyin Table2．Althoughverylarge
degree−dayfactorsforicewerereportedinGreenland

icesheet and Spitsbergen，the degree−dayfactors on

J2

BulletinofGlaciologicalResearch
Table2．Degree−dayfactorsatvariouslocations．UnitsaremmdTlOC1
Ice

9．3

13．8
7．2
8．7
8．3
8．1

Snow Glacier／location

YalaGlacier，CentralNepal
XiaoDongkemadiGlacier，WeStChina
JulylstGlacier，WeStChina

7．9 AXOlO，eaStNepal＋■
3．7 Q．sermia，W−Greenland＊
2．9 Nordbogletscher，WTGreenland＊
NorthGreenland＊

5．9−9．8

18．6

EGIGCampIV，Greenland＊

20．1−22．2

GIMEXprofile，WTGreenland＊
Greisgletscher，Switzerland＊

Spitsbergen＊

13．8

8．3−9．4

Swissglaciers＊5．0−7．0

Patagonia，Argentina＊
StoreSupphellebre■
Gr．Aletschgletscher

6．9−7．1

6．3
5．4

GlaciersinNorway＊

5．5±2．3
6．3±1．0

6．0
7．7
6．4

Arctic Canada＊

3．O FranzJosefGlacier＋
5．7 Satujokull，Iceland♯
4．4 Nigardsbreen，Norway＊
3．8 GlacierdeSarennes，France＊
4．5 Alfotbreen，Norway＊
3．5 Hellstugubreen，Norway＊

6．2
6．0
5．5
＊from BraithwaiteandZhang（2000），Table4．
＊＊fromKayastha et al．（2000a），Table3．

GlacierAXOlO，Yala andXiaoDongkemadiGlaciers
are relatively larger than many other glaciers in

Table2．Braithwaite（1995a）alsomentionedthatlarge

positive degree−day factors only occur withlower

positivedegree−days（lowertemperatures）andthereis

no slgn Oflarge values at hightemperatures．The

Similaritybetweenthedegree−dayfactorsinthepres−entstudyandinsomepartsoftheGreenlandicesheet（Braithwaite，1995a）is，however，againstBraithwaite（1995b）inwhichtheauthor pointed outthatsensible
heat fluxin the Himalayas and Qinghai・Tibetan
Plateau would be nearly half（smallk）at same airtemperaturecomparedtoGreenlandicesheetdueto
thelowerdensityofairinthehighaltitudes．Thismay
COntribute tointerTregionalvariationsin degreeTday

factors．Surprisingly，nOdifferenceindegree−dayfac−
torsorthelargedegree・dayfactorinthe Himalayas
andQinghai−TibetanPlateau，maybeduetoablation

attributed to absorbedglobalradiation at highalti−tude（lower air temperature），because considerable
amountofnetshortwaveradiationwasfoundevenat

and around O OC air temperature on Glacier AXOlO（Fig．6inKayastha et al．，2000a）．

air temperature．It helps to assess the degree−day

factorindifferentclimaticregionandscenario．
Figure5is obtained by plotting the degree−day

factors for seasonalice ablations on Yala，Ⅹiao
DongkemadiandJulylstGlaciers（Tablel）andthe

factor during ice ablation period on Glacier AXOlO（Fig．2in Kayastha et al．，2000a）versus mean air
temperature．Thevariationofdegree−dayfactorswith

respecttomeanairtemperatureisverysimilaronall
four glaciers regardless of being situated at threedifferentgeographicallocations，namelytheNepalese

Himalayas，CentralQinghai−Tibetan Plateau，and

northern periphery of the QinghaiTTibetan Plateau．
Thelargedegree−dayfactorsarefoundonlyatlower
airtemperatureasstatedinBraithwaite（1995a）．

︵
一
．
U
O
−
b
︷
岩
︶
−
○
−
ぷ
﹂
官
金
払
β

3

1

5．Variation of positive degree・day factor withrespecttosumrTlermeanairtemperature

Variation of degree−day factor with respect tomeanairtemperatureisstudiedinordertoknowhow
the degree−dayfactor changeS With respect to mean

0

1

2

3

M￠孤aⅣ虎mp￠如ぐC）

4

5

Fig．5．Seasonaldegree−dayfactorforiceversusmeanair
temperatureonGlacierAXOlO，Yala，XiaoDongkemadi
andJulylstglaciers．

Kayastha et al．

6．Concludingremarks
The monthly degree−day factors forice at two

altitudes5120m and5270m a．s．1．on Yala Glacier

1.7

mous reviewers for their valuable comments．
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