BulletinofGlaciologicalResearch22（2005）3137◎JapaneseSocietyofSnowandIce

3J

Slopelapseratesoftemperaturein DinGad（DokrianiGIacier）catchment，GarhwaL Himalaya，lndia

RenojJ．THAYYEN，）．T．GERGANand D．P．DOBHAL

WadiaInstituteofHimalayanGeology，33−GMSRoad，Dehradun，248001，India
email：renOj＠rediffmail．com（ReceivedAugust20，2004；RevisedmanuscriptreceivedNovember22，2004）

Abstract
Temperaturelapse rate studies of Din Gad catchmentin GarhwalHimalaya were carried out

duringtheablationperiod（May−October）in1998，1999and2000．Temperaturedataforthisstudywas
CO11ectedfromthemeteorologicalstationsestablishedatthreealtitudes（2540，3483and3763ma．s．1．）in

the Din Gad catchment．This data has been analysed to determine suitablelapse rate of slope
temperature fortemperatureindex modeling ofsnow／glacier runoff and mass balance of Dokriani

glacier．Station pair within the alpine zone（3483and3763m a．s．1．）ofthe catchmentshows distinct
Variationsinlapse rate as compared to the va11ey scale（2540and3763m a．s．1．）1apse rate．Yearly

Variationsinthelapseratewithinthealpinezoneofthecatchmentwerehigherthanthevariationsof

Valleyscalelapserate，Whichshow40−50％reductioninthelapseratein1999and2000ascompared
to1998．Itisalsoobservedthatinthevalleyscale，lapseratevalueswerelowerduringthemonsoon
months，COmparedtotherestoftheablationmonths．Howeverthistrendisabsentbetweenthestation
palrlocatedwithinthealpinezone．Duetonon−1inearityoflapserateofDinGadva11eyasobservedin

thisstudy，itissuggestedthatthelapserateofthealpinezoneismostrepresentativeoftheglacier

CatChment，Suitable forsnow／glacier melt runoffand mass balance models．Itis suggested that thelapserateofalpinezoneofthecatchmenthavetobemonitoredformodelinghydrologicalprocesses
OfHimalayanglaciers，ratherthanadoptingthelapseratesofmountainareasofothergeographicallocationsorextrapolatinglapseratevaluesoflowerelevationsoftheHimalayas，aSbeingpracticed
today．

Keywords：GarhwalHimalaya，Dokrianiglacier，Lapserate，Monsoon，Mountain meteorology．

1．lntroduction
Slopelapserateoftemperatureisoneofthemost
important variables for modeling meltwater runoff
from a glacier catchment using temperature index

elingof hydrologlCalprocessesoftheHimalayanglaT
Ciers．Studies on slopelapse rate of temperature are
SparSe from the Himalayan region．A study of de

Scally（1997）from Punjab Himalaya，Pakistan sug−gests that thelapse ratein this reglOnis generally
higher than the values reported from other studies

method．Itisalsoanimportantvariablefordetermin− ranging from O．48to O．780clOOlm1．Researchers
ingtheformofprecipitationanditsdistributionchar−
have used wide−ranginglapse rate of slope air tem−
peratures ranging from O．65to O．98℃1001mlfor
acteristics during summer ablation months over therunoffmodelingstudies（Bagchi，1982；Deyetal．，1989；
glaciers under the monsoonalregime（Higuchietal．，1982；Thayyen，1997；Thayyen etalリin press）．Tem− Upadhyay，1995）．Manyothersnowmeltrunoffmodels

peraturelapseratevaluesarealsocriticalinthestudy
Of accumulation characteristics of the glaciers underfromvariousreglOnSuSedrangeofvaluesclosetothe

Cingthetemperaturelapserateinthemountaincatch−

paperinvestigatethevalidityoftheseslopelapseratetheinfluence of monsoon（Ageta and Higuchi，1984）．
Barry（1992）discussedthecomplexprocessesinfluen−environmentallapse raterangingfromO．55toO．650c
lOO1m1（Martinec，1975；Ageta etal．，1980；Rango，1983；Ikebuchietalり1986；Kayasthaetal．，1999）．This

ments andits variations∴HencereglOn SpeCificinfor−

ValuesformodelingglaciaユhydrologユCalprocessesof

mation of temperaturelapse rate andits variations
areessentialrequirementfortemperatureindexmod−

GarhwalHimalaya，Where theinfluence of monsoonduring summer ablation periodis very prominent．

Bulletin ofGlaciologlCalResearch

J27851■Fig．1．Location map of Din Gad catchment showing Tela，Gujjar Hut and Base campmeteorologlCalobservatories．Figure also show snowline positionsin the Din Gad
CatChmentinthefirstweekofMayduringdifferentobservationyears．

Tablel．Characteristics ofclimate stationsin the Din Gad catchment．

Station Elevation

Site description Surface type Possibility ofKatabaticeffect（ma．s．1．）

Tela2540

NESparseGujjarHut3483

Meadow close to the GrassPlain
ground forestBaseCamp3763

PlainMeadow above theground treeline

Openinglnthe
COniferforest

Thisstudy focusesonthe monthly and yearly varia−
tionsin thelapse rate of slope air temperature be−
tween three station pairs during1998，1999and2000
ablation months．

2．Studyarea
DinGadva11eyispartofheadwatercatchmentof
GangariverintheGarhwalHimalaya．Thiscatchment

has NW aspect andlies betweenlatitude30048′to30053′Nandlongitude78039′to78051′E．Forestedarea

Ofthecatchmentcover54％andAlpinemeadowsand

graSS

No
Moderate

SparsegraSS

Yesto2300−2500min winter．Duringthe yearsofnormal
wintersnowfa11snowlinerecedesto3800ma．s．1．inthe

beginningofthemonthofMay．

3．Methods
ThreemeteorologlCalstationswereestablishedin
the Din Gad catchmentin1998to monitor the mete−
OrOlogicalvariables．Air temperature data at these
Stations were collected during the summer ablation

months（May to October）．These stations were estab−

1ished along the 23km trekking route to Dokriani
glacierscover31％and15％respectively（Fig．1）．Total glacierfromtheroadheadatBhukkivillage．Thefirstcatchmentareais77．8km2．DinGadjoinswithBhagi−

StationatTelaislocatedata heightof2540ma．s．1．，inSeptember．July and August account for nearly40−
50％of rainfallduring the ablation months．Din Gad

SeCOnd station at Gujjar Hut（3483m a、S．l．）has beenrathiRiver near Bhukkivillage．Monsoon hits Din
Gad catchment afterJune15 and prevailtillmid

CatChmentis one of the glaciated catchmentsin theGarhwalHimalaya，Whichfirst encounters monsoon
WindsasitmovesuptothehigherreachesofBhagira−thicatchment．Hence Din Gad catchmentexperience

goodmonsoonrainfa11（1100to1600mm，duringMay−October）．DinGadcatchmentextendedfrorn1800mto

6600mandseasonalsnow covergenerally reachesup

a large open space surrounded by the Oak and Pine
forest on the va11ey slope having NE aspect．The

established on alpine meadows close to the conifer
forest．Thisstationisontheplaingroundwe11above

the valley bottom．The thirdstation at Dokrianigla−
CierBasecamp（3763ma．s．1．）isonthealpinemeadowsabovethetreeline．Detailedtopographicdescriptions

OfmeteorologicalstationsaregiveninTable−1．These

Stationsweremcmitoredfrom3Mayto23November
in1998，8Mayto15Novemberin1999and15Mayto23

Thayyenetal．

、？， ∫Table2．Average monthly Lapse rateOC（100m）■lfordifferentstationpairs

duringthreeyearsofobservation．

Octoberin2000．Air temperature measurementsin
these three stations were carried out from 0530 hrs to2030hrs with three−hourinterval．Theinstruments

Were placedinside the Stevenson screen atl．6m

above the ground．In1999，thermographs werein−stalledatTelastationbetween25Juneand16Novem−

berandatBasecampfrom7Julyto13Novemberfor

DinGadcatchment．Highestmeanmonthlylapserate
Value recorded among the station pairs was O．81CC
lOOlm1in May1998between Tela and Gujjar hut
Stations．Monthly variationsinlapse rates between
GujjarHutandBasecampstationwashighest，Within
therangeofO．710clOO1m1inJuneandJulyof1998

to o．2lOclOO 1mlin October1999 with certain
COntinuousrecordingoftemperature．Meandailytem− periodsin October and Novemberexperiencing tem−
peratureinversioncharacteristics（Table2）．Thesesta−
peraturefortheseperiodswerecalculatedfromhour−

1y temperature record from the thermograph andCOmparedwiththemeandailytemperaturecalculated
from dry bulb temperatures．On an average mean
dailytemperaturederivedfromdrybulbtemperature
isl．00c higher than the mean daily values derived
from hourly temperature at Base Camp and O．50c atTela．Inthispaperlapseratehasbeencalculatedfrom
the mean daily temperature derived from dry bulb
temperaturebyaveraglngthetemperaturesmeasured

tionpairinthealpinezoneoftheDinGadcatchment
Show distinctlylowerlapse ratein1999and2000as
COmparedtothe1998values．LapserateinpeakablaT
tionmonthsofJune，JulyandAugustin1999and2000

WaS40−50％1esscomparedtothevaluescalculatedfor

thesamemonthsin1998．Largevariationsinthelapse
ratebetweenBaseCamp−GujjarHutpairispossibly

duetothevariationsinthedistributionofsnowcoverintheseyears．Figure−1showsthesnowlinepositions
at O530，0830，1130，1430，1730and2030hrs．at three
ObservedinthemonthofMayduringtheobservation
years．Theyear1998experienced heavysnowfalldur−
Stations．This data has been collected consistently

during May −November period from allthe threeStationsforthreeconsecutiveyears．
4．Results and discussion

ingDecembertoMarchascomparedto1999and2000．

Infact，theyear1999experiencedlowestsnowfall（144mmw．e．）attheBasecampsincethestudiesstartedon
the Dokrianiglacierin1992．Whereasin2000，Winter
SnOWpreClpitationattheBasecampwas210mm w．e．

イ．J．．1Jr川JJ申（川（り・（−（汀什！・（け山J高JJ∫わJ∫／（埴（−J（ゆゴ（リ￣（〟ぐin which most of the wintersnowfalloccurredin theglVenin Table2．During this period monthly varia−

ust monthsin1999and2000were close to thelapse

Figure 2shows the dailylapse rate variations
between the selected station palrS from which themonthly mean values were calculated，Summary ofmonthlylapse ratesin three observation years aretionsoflapserateinsummermonthshavebeenmini−

lastquarterofthewinterseasonandmeltedawayfast
from thelowerreaches of theGujjarHut catchment
duetothehighertemperaturesinApril．

Mean monthlylapse rateofJune，July and Aug−rate reported by Legates and Willmott（1990），0．30Oc
mumbetweentheTela−BaseCampstationpalrS，rang− lOO1m1forJulyatanaltitudeof3010minHimalaya．
ing between O．71LO．50OclOO1m1，With an average It could be possible that the sparse snow cover re−lapserateofO．590clOOlm1．Lapseratebetweenthese Sultedin more homogenous warmingin the higher
altitude，reSultinglnlowertemperaturevariationsbe−
two stations represents the valley scalelapse rate ofBulletin ofGlaciologicalResearch

．てイ

1盲○邑
U
㌔l巴邑
dJ〇．

5 0〇．

2 51・∽︵∈菩2l︶ 5UO
ひ ∞1空
邑 0030

Fig．2．Daily variationsin thelapse ratevalues in summer months within the Alpine
ZOneandin thevalleyscaleduringthe
three yearsofobservation．

tween the meteorologlCalstations．Temperature at

meteorologicalstationslocated at thelower altitudedepth ofsnowinfluences thelapse rate between theStationsinthealpinecatchment．

SeemS tObe unaffected by thevariationsinthesnow

COVer at higher altitude．Thisis evident from thelower monthly variationsinlapse rate during thesethreeyearsbetweenTela−BasecampandTela−Gujjar
hut pairs，eXCeptin the month of May，1998．Higher

lapseratevalueinMay1998betweenTela−GujjarHut
pair was resulted due to the closeness of Gujjar hut
StationtothesnowlineinthemonthofMay，Which
Offers greater temperature variations between these
StationswithrespecttotheTelastation．Henceitcan
be suggested that the closenessofsnow to the mete−

OrOlogicalstations，lateralextent of snow cover and4．2 エ（ゆSe和才β〃αrよαfわ花王乃椚077SOO77∽0乃gゐざ
Inthevalleyscale，prOminentandconsistentvar−

iationsin theslopelapserateoftemperatureduring
themonsoon months havebeenobservedduringthe

Study period．The results showlowerlapseratedur−ing the monsoonalmonths betweenTela−Basecamp

andTela−GujjarHutstationpairs（Fig．2andTable−2）．
Howeveralpine zone（Gujjar Hutq Basecamp）ofthe

CatChment did not show such a trend．Station pairWithinthealplneZOneShowshigheryearlyvariations
butlesser monthly variations during the monsoonThayyenetal．

months．From theseobservationsitcanbesuggested
thatthelapseratebetweenthestationpalr，inwhich
atleast one of the stationsis uninfluenced by theSnOW COVer（outside the alpine zone），Show reduced

lapse ratein monsoonalmonths，eSPeCiallyinJuly

and August，Whichranged between O．59−0．50℃100l
m1．Allthethreestationsrecordedhighrelativehu−

midityvaluesinmonsoonmonthsrangingfrom69to95％，SuggeStingupwardmovementofairundersatu−

rated adiabatic conditions andlarge quantities ofla−tentheatreleaseduringcondensationandrainfall（deSca11y，1997）．Thisconditionsprobablyleadstoamore

homogenoustemperaturedistributionresultinglnre−
duced valley scalelapse ratein monsoonalmonths．
Theabsenceofsuchatrendinlapseratederivedfrom
the stationswithin thealplneZOneSuggeStS homoge−neity of thermal regime of alpine zone through theablationmonthsthatpersistedevenduringthemon−
SOOn mOnths．
4．3．SβJecJgo77q／sわ♪eJα♪seれユねノbγ∽0（プe肋ggJαC≠eγ
ゐγdγ0わggcαJ♪γOCβSSeざTheresultsofthisstudy raisesapertinentquesT
tion about the selection ofsuitable altitudinalrange
formonitoringslopelapserateforsnow／glaciermelt
runoffmodels，Whichwouldbemostrepresentativeof
the glacier catchment．Comparison of monthlylapse

ratesderivedfrom threestationpalrSShowconsideトable variationin thelapse rate values between diffeT
rent station palrS．Three year average of summer

lapseratebetweenTela−BasecampandTela−Gujjar
hut station pairs are O．59℃and O．650clOOlm1re−SpeCtively，Where as average summerlapse rate of

Gujjar Hut−Base camp pairin1998was O．620clOO1
m1andaverageof1999and2000wasO．360clOO1m1．

Henceitcanbesuggested thattheuseofvalleyscale
lapse rate to determine the point temperatures athigher altitude may be feasible but calculation oftemperaturedistributionovertheglacierbyextrapo−
1ationasrequired fordistributedglacierrunoffmodT
els using valley scalelapserate mayintroducelarge
errors．Thisstudysuggestsachangeinthelapserate
above3000−3500moftheDinGadcatchmentalongthe

main axis of the valley．Lapse rate below thiseleva−

tionshowslessmonthlyandyearlyvariationandthe
StationpalrabovethiszoneshowssubstantialmonthT
ly and yearly variations，mainly attributed to theSnOW COVer Variations and related manifestations．

Consideringthesealtitudinalvariationsinlapserate，
itis suggested that thelapse rate observedin thealpinezoneofthecatchment（Gujjarhut−BaseCamppair）isthemostrepresentativeofthelapserateofthe
glacier catchment．However extrapolation of thesevalues over the glacier is bound to generate someerrors due to the fact that both these stations are in

SnOW／ice free zonein the summer ablation months．

Howeveritis prudent to assume that thelapse rate

ユう

between thestation palrOVertheglacierwi11belessthan thelapse rate of closest pairsinice free area，
especially when the glacier catchment experience
heavymonsoonalrainsin thesummerablationmon−ths．Hencemostaccuratelapseratevaluesforsnow／ice meltmodelonlycanbederivedfromstationpalr
establishedovertheglacieritself，buthasoperational
difhcultiesin thefield conditions of Himalayan gla−
Ciers．Henceitcan besuggested thatthefuturelapse
rate studies forglaciologlCalstudiesin the Himalaya
needs to be concentrated in the alpine zone of theCatChment．More comprehensivestudiesare required

to establish the controlof snow cover，Slope，aSpeCt，
rainfalland windetc．onslopelapserateoftempera，ture to develop predictive model for temperature
lapserate variationsinaglaciated Himalayan catch−ment．Whileconsideringtherangeofyearlyvariation
Observedin thelapse rate within the alpine zone，modelingslopelapserateisanimportantobjectiveto
beachievedforthesuccessfulmodelingofhydrologlT
CalprocessesofHimalayanglaciers．
This study suggests that the valley scale slope
lapse rate values do not necessarily represent thelapse ratesofthealplneZOne．ThermalreglmeOfthe
alpine zone is probably regulated by the seasonal
SnOWCOVereXtentanditsthickness．Thisstudyagrees
With the generalassumption madein many snowT
meltrunoffmodelsthatthelapserateoverthelarge

rangeofelevationislinear（Deyetal．，1989．，Bloschletal．，1991）．But the non−1inearityin slopelapse rate

Observedin this study between thesubzonesofthe
Va11eysuggeststhattheextrapolationofvalleyscale
lapse rate to the glacier catchment may not yielddesired result．

Results reported in this paper have many fold
implicationsin understanding and modeling hydro−
logicalprocessesofHimalayanglacierreglmeS．Figure
3 demonstrated significant difference between ex−
trapolated degree day values at various altitudinalbands of Dokrianiglacier using both standardlapse
rateofO．60clOO1m1andthecalculatedlapserateof
Alpine zone of the Din Gad catchmentin1998，1999
and2000summer ablation period．If we follow theCalculatedlapse rate for the Alpine catchment，itis
evidentthatthehigherreachesoftheDokrianiglacierexperienced higher temperature regimein1999and2000eventhoughthepositivedegreedaysofsummer
months at Base campln1998was much higher thanthat of1999 and 2000．Thisis also reflectedin thehigher melting of glacier above 4500m as observed
duringthestakemeasurementsformassbalancestud−iesofDokrianiglacierin these three years（Dobhaletal．，Unpublished）．This also enhances the monsoon

rainfallcomponentintheglacierdischarge（Thayyenetal．，inpress）andraisesseriousquestionsregarding

thesummeraccumulationcharacteristicsofthesegla−Ciers．Hence this study suggest that the use oflapse

BulletinofGlaciologlCalResearch

J6鼠疇
凸窒L謬凸ぎ≡芸d3762 4000 4300 4600 4900 5200 5500 5800 6100 6400
Altitudelm）
Fig．3．Distribution of degree days at different altitudinalzones of the glacier byextrapolation ofpositive degree days at Base camp（3763m a．s．1．）using standard
lapserateofO．60c／100mandestimatedlapserateofAlpinezone，rate close to the environmentallapse rateasdonein
manysnowmeltmodelshastobeadoptedcautiously
for Himalayan conditions，eSpeCiallyin the regionsundertheinfluenceofheavymonsoonactivity．
5．Conc（usionsl．The slopelapse rate of air temperaturein thealplne ZOne Of the Himalayan catchment show
distinctvariationwiththevalleyscaleslopelapse

On HimalayanGlacio10gy．We thank Director，Wadia

InstituteofHimalayanGeology（WIHG）forproviding
theinstitutionalfacilities．
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