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InternationalJournalofWaterResourcesDevelopment,2015 http://dx.doi.org/10.1080/07900627.2015.1005731 The glaciers of the Hindu Kush Himalayas: current status and observed changes from the 1980s to 2010 Samjwal Ratna Bajracharyaa*, SudanBikash Maharjana,Finu Shresthaa, Wanqin Guob, Shiyin Liub,WalterImmerzeelc andBasanta Shresthaa aInternationalCentreforIntegratedMountainDevelopment,Kathmandu,Nepal;bColdandArid RegionsEnvironmentalandEngineeringResearchInstitute,ChineseAcademyofSciences,Lanzhou, China;cDepartmentofPhysicalGeography,UtrechtUniversity,theNetherlands (Received25August2014;accepted6January2015) ThefateoftheHinduKushHimalayanglaciershasbeenatopicofheateddebatedueto 5 their rapid melting and retreat. The underlying reason for the debate is the lack of 1 0 systematiclarge-scaleobservationsoftheextentofglaciersintheregionowingtothe 2 h high altitude, remoteness of the terrain, and extreme climatic conditions. Here we rc present a remote sensing–based comprehensive assessment of the current status and a M observedchangesintheglacierextentoftheHinduKushHimalayas.Itrevealshighly 5 heterogeneous,yetundeniableimpactsofclimatechange. 0 01 Keywords:Landsat;remotesensing;glacierareachanges;decadal 1: 2 at 7] Introduction 2 8.1 TheHinduKushHimalayan(HKH)regionisthefreshwatertowerofSouthAsia.Ithasthe 2 highest concentration of snow and glaciers outside the polar region, and thus has been 2 6. calledtheThirdPole(Dyhrenfurth,1955).Thesnowandglaciermeltwaterplaysapivotal 9 1 1. roleinthewatersupplyforthoseriverbasinsthatareariddownstream,inparticularwhere [7 there are large irrigation systems that depend on upstream water resources. Mountain y b ranges are particularlysensitivetoclimatechange, andthe HKH region is noexception. d e Changesintheglaciersmayhaveasignificantimpactonthequantityandtimingofwater d a availability(Rabateletal.,2013).Acomprehensiveunderstandingoftheextentandnature o nl ofchangesinglacierswillsupportdownstreamhydrologicalplanningandwaterresource w o management (Rankl, Kienholz, & Braun, 2014). We focus on the development of the D glacierareaoverdecades,tounderstandfuturechangeandofferapossibleevaluationof future water quantity and availability. Thereisalargevariationinglacierresponseintheregionowingtothediverseterrain andclimates.Therearetransitionsfromcoldertodrierandawetter(monsoondominated) towarmerclimatefromwesttoeastandfromnorthtosouth.Overall,theglaciersinthe regionareretreatingorshrinkingandthinningduetoclimatechange(Fujita&Nuimura, 2011; Kargel, Cogley, Leonard, Haritashya, & Byers, 2011; Kaser, Cogley, Dyurgerov, Meier, & Ohmura, 2006; Scherler, Bookhagen, & Strecker, 2011; Zemp, Hoelzle, & Haeberli, 2009). Some studies report a different behaviour of glaciers in the Karakoram (Hewitt,2005,2011;Scherleretal.,2011),whichmaybeexplainedbyapositivetrendin winterprecipitationandlimitedwarmingduringthemeltseason(Archer&Fowler,2004; Tahir,Chevallier,Arnaud,&Ahmad,2011).Climatechangealsoleadstotheexpansion *Correspondingauthor.Email:[email protected] q2015TheAuthor(s).PublishedbyTaylor&Francis. ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttribution-NonCommercial-NoDerivs License (http://creativecommons.org/Licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproductioninanymedium,providedtheoriginalworkisproperlycited,andisnotaltered,transformed,orbuiltuponinanyway. 2 S.R. Bajracharya et al. and formation of glacial lakes, which could lead to an increase in glacial lake outburst floods.Anumberofsuchfloodshavealreadybeenreportedintheregion(Bajracharya& Mool, 2010;Bajracharya, Mool, &Shrestha, 2007; Richardson &Reynolds,2000). Despite the importance of the HKH region, there is a lack of consistent and homogeneous glacier data. Most studies focus on small areas and present a regional overview.Severalinterlinkedglobalglacierinventoryinitiativesexist,suchastheWorld Glacier MonitoringService (Haeberli, Bo¨sch, Sherler, Østrem,& Walle`n, 1989), Global Land and Ice Measurements from Space (GLIMS) (Raup et al., 2007), the GlobGlacier project (Paul et al., 2010), and the Randolph Glacier Inventory (Pfeffer et al., 2014). However, none of these initiatives has resulted in a consistent and complete glacier inventoryfortheHKHregion.Sucharegionalglacierdatabase,basedonastandardized method, is therefore urgently needed as a benchmark against which changes can be assessed.Recently,aninventoryofglaciers,including debris-covered (DC)glaciers,has been developed for the entire HKH region using remote-sensing data (Bajracharya & Shrestha, 2011; Bolch et al., 2012). The glacier outlines were compiled using a semi- 5 1 automatedremote-sensingmethodwithtopographicinformationobtainedfromthevoid- 0 h 2 filled version of the Shuttle Radar Topography Mission digital elevation model (SRTM rc DEM). The comprehensive assessment of glaciers is based on the status as of 2005^3 a M years,whereastheextentofglacierchangeisbasedonatemporalseriesofLandsatimages 05 since the 1980s. 1 0 1: 2 at Study area 7] The HKH region extends from 15.958 to 39.318 N latitude and 60.858 to 105.048 E 12 longitude,encompassinganareaofabout4.2millionkm2andextendingacrossallorpart 8. 2 oftheeightcountriesofAfghanistan,Bangladesh,Bhutan,China,India,Myanmar,Nepal 2 6. andPakistan(Bajracharya&Shrestha,2011).Therearehighconcentrationsofsnowand 9 1 glaciers in the mountains of the region. Meltwater from snow and glaciers feeds the 10 1. 7 largest river systems in Asia: the Amu Darya, Indus, Ganges, Brahmaputra, Irrawaddy, [ y Salween,Mekong,Yangtze,YellowandTarim(Immerzeel,VanBeek,&Bierkens,2010; b d Kaser, Großhauser, &Marzeion, 2010). e ad Four representative basins were selected for decadal glacier change analysis: the o nl WakhanCorridorinAfghanistan,theShyokBasininPakistan,theImjaValleyinNepal, w o and the Lunana regionin Bhutan (Figure 2). D Data and methods Data This study used more than 200 orthorectified Landsat 7 ETMþL1G scenes from the Global Land Cover Facility (http://www.landcover.org) from 2005^3 years. Images with a minimum of cloud and snow cover were selected. The Landsat 7 ETMþimages sufferfromascan-linecorrectorfailure,causingawedged-shapedscan-to-scangap.Prior to analysis, the scan-line gaps were filled using a specifically developed software extensionintheENVIimage-processingpackage.Weuseda90mresolutionSRTMDEM toderive the attributedata for each glacier. For the decadal glacier change analysis, Landsat 5 MSS, Landsat 7, and Landsat 7 ETMþimages were used. To delineate the glacier outline, the images should have low snow and be cloud-free; however, the freely downloadable images rarely meet the ideal requirements, hence images must be selected from a range of years rather than a single International JournalofWaterResources Development 3 year.Landsat5MSSimagesfrom1976to1979wereusedtoapproximate1980(hereafter referred to as ,1980); Landsat 7 TM images from 1988 to 1992, for 1990; Landsat 7 ETMþfrom1999to2001,for2000;andLandsat7ETMþfrom2009to2011,for2010. Ineach case, the images with the least snow cover andno cloud cover wereselected. Glacier outline for 2005 Most glaciers are clearly visible as a clean-ice (CI) surface, but some have debris cover (DC) at their tongues. The spectral uniqueness of CI glaciers in the visible and near- infrared bands of the electromagnetic spectrum allows the use of simple algorithms. However, the delineation of DC glaciers poses challenges because of the non-unique spectralsignatures andillumination errors due toeffectsfrom surrounding materials. Theimageswerefirstsegmentedusingobject-basedimageclassificationineCognition software(Figure1)withdifferentparametersettings(typeofvariableandthresholdvalue) for CI and DC glaciers (Bajracharya, Maharjan, & Shrestha, 2014). The Normalized 5 1 0 2 h rc LANDSAT and SRTM a M 5 1 0 Object-based image classification 0 1: 2 at ] 7 2 NDSI Slope angle 1 8. Classify image objects 2 2 oaded by [71.196. CI Glaciers LanSdl o&Np eWD VaanItegrl eMask g the misclassifiedmage objects Land &N NWDDaVStIeIr Mask DC Glaciers wnl erini Do Elevation Filt Elevation Area ≥ 0.02 sq.km Manual correction Attribute generation Glacier Map/Database Figure 1. Flow chart of methodology for delineation of clean-ice (CI) and debris-covered (DC) glaciers. Note. NDSI¼Normalized Difference Snow Index. NDVI¼Normalized Difference VegetationIndex. 4 S.R. Bajracharya et al. Difference Snow Index (NDSI) (Hall, Riggs, & Salomonson, 1995; Racoviteanu, Williams,&Barry,2008)wasusedtomakeaninitialselectionofsegmentsforCIglaciers. Inthenextfilteringstep,differentvariablessuchastheNormalizedDifferenceVegetation Index (NDVI) (for vegetation), Land and Water Mask (for open water), mean slope and mean altitude were determined to identify misclassified image objects, which were excluded.TheDCglacierswerecapturedfromthesegmentedimageobjectsusingaslope threshold value of less than 258, which captures the entire DC glacier area including vegetation, water, snow and surroundings. As DC glaciers only occur below 6000 masl, image objects outside the elevation range of 3000–6000 masl were excluded. Further threshold values of NDVI (.0.3), LWM (50–115.8) and NDSI ($0.005) were used to excludevegetation,snow,andlandandwaterbodies,respectively.Thefilteringstepswere notnecessarily done inthisorder. TheseprocessessatisfactorilydelineatedtheoutlinesofCIandDCglaciers,whichwere thenmergedtoasinglefile.Imageobjectswithasurfaceareaoflessthan0.02km2werethen omittedandtheedgesofthepolygonssmoothed.Theglacierimageobjectsweretransferred 5 1 toaGIS-compatibleformatandfinalizedbymanualeditingatascaleof1:20,000bydraping 0 h 2 overrespectiveimagesandverifyingwithhigh-resolutionimagesfromGoogleEarthina rc GIS environment. Special attention was given to defining the outline and snout of the a M glaciers. CI glaciers require minor manual corrections; DC glaciers need careful manual 05 correctionsbecausetheycloselyresemblemorainesandbarerockoutcrops. 1 Forthetime-seriesanalysis,glacierpolygonsweregeneratedfor2010fortheWakhan, 0 1: Shyok,ImjaandLunanaareasusingthemethoddescribedabove.Theglacieroutlinesfor 2 at the other decades were then generated by manual editing on the recent glacier outline, 7] overlaying the Landsatimages from 2000,1990,and ,1980. 2 1 8. 2 2 Glacier attributes 6. 9 1 Attributedataareassignedtoeachglacierpolygonfollowinginternationalconventionsset 1. 7 outbytheWorldGlacierMonitoringService,theGlobGlacierinitiative,andtheGLIMS [ y community (Mu¨ller, Caflisch, & Mu¨ller, 1977; Paul et al., 2010; Raup et al., 2007). For b d each glacier, a GLIMS ID, location, area, elevation range, aspect, average slope, mean e d glacierthickness,andestimatedicereserveswerestoredinthedatabase.Furtherdetailsof a o nl the method are given by Bajracharya and Shrestha (2011). w o D Uncertainty The uncertainty of the glacier area depends on image resolution and snow cover. To minimize the uncertainty, images with the least snow cover were used, and the automatically derived glacier polygons were refined manually by draping over high- resolutionGoogleEarthimages.Themaximum offsetoftheboundarycannotbegreater thanhalfoftheimageresolution(i.e.^15mforTMandETMþand^30mforMSS). The steps todefine the uncertaintyof the glacierpolygonwereas follows: . Buffering of mapped glacier polygons with half of the image pixels . Calculationofthetotalnumberofpixelsboundedbyeachbufferedglacierpolygon . Calculation of buffered area by multiplying total pixel count and the area of one pixel . Uncertaintyofthemappedglaciertakenasthevarianceinglacierarea – thatis,the difference between actual glacier area (mapped glacier polygon) and buffered glacier polygon area International JournalofWaterResources Development 5 The uncertainty of the glacier areas in the present study was 7% for ,1980 and 6% for 1990, 2000 and2010. Results Glaciers inthe HKH region In total, 54,252 glaciers were identified within the HKH region, with a total area of 60,054km2andestimatedicereservesof6127km3(Figure2,Table1).Thisrevealsthat only1.4%oftheHKHregionisglaciated;thetotalicereservesareroughlyequaltothree times the annual precipitation (Bookhagen & Burbank, 2006; Immerzeel et al., 2010). Thereisalargevariationbetweenriverbasins;thelargesttotalglacierareasarefoundin the Indus,Brahmaputra andGanges basins,respectively (Figure3). Over60%ofthetotalglacierareaoftheHKHislocatedintheelevationrange5000– 6000masl (Figure4).Theglaciersbelow 5700masl areparticularly sensitive toclimate change unless they are covered by thick debris (Bajracharya et al., 2014). The Indus, 5 1 Ganges and Brahmaputra basins have 79%, 60% and 77% of their total glacier area, 0 h 2 respectively,belowthiscriticalelevation.CIglaciersatlowaltitudeandsmallglaciersare rc the most sensitive glaciers to climatechange inthe HKH region. a M Athickdebrislayerhasastronginsulatingeffect;sub-debrismeltratescanbeafactor 05 of5to10lowerthanforCIglaciers(Hagg,Mayer,Lambrecht,&Helm,2008;Mihalcea 1 etal.,2006).Atotalof32,000km2oftheglacierareawascategorizedaseitherDCorCI 0 1: (glacierswithinChinawerenotdifferentiated).Ofthis,9.7%overallwasclassifiedasDC, 2 at and 9.3%, 11.1% and 12.6% of the differentiated area in the Indus, Brahmaputra and 7] Ganges basins, respectively. DC glaciers are mostly found at the frontal part of valley 2 1 glaciersandhaveanaverageslopeof128 – muchlesssteepthanCIglaciers,whichhave 8. 2 anaverage slopeof 258(Bajracharya & Shrestha, 2011;Bolch et al., 2012). 2 6. 9 1 1. 7 [ y b d e d a o nl w o D Figure2. TheHinduKushHimalayas(brownpolygons),majorriverbasins(blackpolygons)and glacier outlines (blue shaded polygons); red letters indicate the representative glaciers for which decadalchangesareshown.Note.A¼WakhanCorridor,Afghanistan.B¼ShyokBasin,Pakistan. C¼ImjaValley,Nepal.D¼Lunanaarea,Bhutan. 6 S.R. Bajracharya et al. KH 1,8135,7219838952 54 6.969 isnot H 8,993,7027.439.267.6103.54,2n/an/a60,09266,128,802,40n/an/a n/a n/a n/an/a251.11 area H Interior n/a909,82429.6939.2878.31100.547,351n/an/a7,53584563.16,6093,994n/an/a n/a n/a n/an/a241.02 oftheHK m 039 art Tari 929,026,7234.7436.7475.5686.811,091517322,310239378.66,4623,94042776462 3940 5235 1710262.12 sin).P a 8 b Yellow 1,073,16250,54033.2938.2598.61101.87189n/an/a137219.25,7104,151n/an/a n/a n/a n/an/a260.73 einterior h h 2015 ongYangtze 3222,065,763876565,10228.20335.77590.556103.891,661n/an/a1,66055121.416,27012,972n/an/a n/a n/a n/an/a271.00 2km(excludingtovered. Marc Mek 841,138,28.333.794.198.7482n/an/a2351010.76,362,89n/an/a n/a n/a n/an/a260.49 5,898bris-c 9e nloaded by [71.196.228.127] at 21:01 05 HinduKushHimalayanregion. Basin GangesBrahmaputraIrrawaddySalween 1,001,019528,079426,501363,778244,806432,480202,745211,12227.5327.4928.0628.3831.4231.0328.7732.7677.9882.0398.1791.588.797.7697.8698.717,96311,4971332,1135,6221,18635n/a8101480n/a9,01214,020351,352177204340793.51,302.61.387.78,8068,3314,2566,4713,2732,4355,6953,7863,6103,7074,256n/a8,8068,3315,695n/a 3,2733,882n/an/a 6,0095,828n/an/a 282525n/a1213n/an/a282525251.131.220.270.64 ¼22,446km;10basins’areaintheHKHregion2,7¼¼plicable(asnotevaluated).CIclean-ice.DCd Dow asinsofthe Indus 1,116,086555,45030.4537.0869.3681.6518,49515,6351,97021,1939262,696.18,5662,4092,7238,566 2,409 5,913 2511241.15 ¼Harea4,19¼n/anotap Table1.Glaciercharacteristicsintheb AmuParameterUnitsDarya 2645,726BasinareatotalKm2BasinareaintheHKHkm166,686Latitudeminimumdegree34.57Latitudemaximumdegree38.35Longitudeminimumdegree67.63Longitudemaximumdegree74.88Numberofglaciersunit3,2772CIglacierarea*km2,4062DCglacierarea*km1612Totalglacierareakm2,5662Largestglacierareakm403TotalicereservesKm162.6Highestelevationmasl7,213Lowestelevationmasl3,131CIelevationminimum*masl3,415CIelevationmasl7,213maximum*DCelevationmasl3,131minimum*DCelevationmasl5,466maximum*MeanCIglacierslope*degree25MeanDCglacierslope*degree12Meanslopedegree242Averageglacierareakm0.78 Note.BasedonUTM,WGS84projection.HKincludedineitherthe10basinsortheinterior.*ExcludingglaciersinChina. International JournalofWaterResources Development 7 9,000 8,000 7,000 sl) a m 6,000 n ( o ati 5,000 v e El 4,000 Amu Darya Indus Ganges Brahmaputra Irrawaddy Salween 3,000 5 Mekong Yangtze Yellow 1 0 Tarim Interior 2 h 2,000 c r 0 200 400 600 800 1000 1200 1400 1600 a M 5 Glacier area (km2) 0 01 Figure3. GlacierhypsographsofthemajorbasinsintheHKHregion. 1: 2 at ] 27 20,000 1 8. 18,000 2 2 16,000 6. 19 2m) 14,000 1. k 12,000 y [7 ea ( 10,000 d b Ar 8,000 de 6,000 a o 4,000 nl w 2,000 o D 0 2000 - 2500 - 3000 - 3500 - 4000 - 4500 - 5000 - 5500 - 6000 - 6500 - 7000 - 7500 - 8000 - 8500 - 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 Elevation (masl) Figure4. Glacierareadistributionin500melevationbandsintheHKHregion. Glacier change inthe selected basins ThetimeseriesanalysisshowedthattheglacierareaintheWakhanCorridorisrelatively stable(Figure5,Table2).Someglaciersshowedsmalllossesofareaoflessthan5%inthe period 1980–1990; there were more noticeable area losses of 4–36% in 1990–2000, while most areas were stable or even increased in the period 2000–2010. Over the 30 years,mostglaciersshowedaslightreductioninglacierarea,whichwasmostprominent attheglaciertongues(Figure5,panelA).Amongtheindividualglaciers,no.8increased slightlyinareaoverthe30years;nos.1and6showedsmalllossesofaround5%ofarea; 8 S.R. Bajracharya et al. 5 1 0 2 h c r a M 5 0 1 0 1: 2 at ] 7 2 Figure 5. Representative examples of glacier change in different parts of the Hindu Kush 1 8. Himalayanregion.Note.A¼WakhanCorridor,Afghanistan.B¼ShyokBasin,Pakistan.C¼Imja 22 Valley,Nepal.D¼Lunanaarea,Bhutan. 6. 9 1 1. thesmallestglacier,no.2,hadamarkedlossof27%ofarea;andallotherglaciersshowed [7 losses of10–12% ofarea. y b Most of the glaciers in the Shyok Basin lost area and retreated in the period 1980– d e 1990,showedlittlechangein1990–2000,andremainedstaticoradvancedin2000–2010. d a Overthe30years,mostglaciersshowedsomelossofarea,buttherewasalmostnochange o nl inthe area of the largest glacier,no. 5. w o The glaciers in the Imja Valley in Nepal and the Lunana region in Bhutan showed D similartrends,withthehighestlossesofglacierareaobservedintheperiods1980–1990 and2000–2010.TheglaciersintheHimalayaareretreatingfasterthanthoseintheHindu Kush and Karakorum, with losses over 30 years of 5–55% of area. The West Lhotse Glacier in the Imja Valleywas the fastest-retreating glacier ofall those studied. Discussion The evaluation of glacier status using remote sensing provides baseline information on extension,aspect,slope,elevation,andtypeofglaciers.Completeinventoriesfordifferent timeseriesareneededtofullyunderstandthelikelyfuturechallengesforglaciermeltwater resources and glacial hazards. The glaciers of the HKH region are situated above 3200 masl, and field-based mapping is difficult given the high altitude, remoteness, harsh climatic conditions and lack of logistical support. This limits our understanding of the spatial patterns of glacier dynamics and their sensitivity to climate variability across the Himalayasatalargescale.UntilthelaunchofLandsatTMin1982,compilationofglacier International JournalofWaterResources Development 9 0 1 0 4380950311527941846396240363522 80–2 25.227.211.210.210.24.210.3.216.29.212.26.0.22.210.29.22.229.210.227.254.230.216.217.213.25.218.229.214.221.28. 9 1 0 %) 01 0300040800563600573047302383016 nge( 00–2 0.14.1.0.22.2.0.14.21.0.10.22.0.0.0.2.0.27.1.27.232.215.29.25.23.25.27.23.23.27.25. a 0 h 2 c a are 00 Glacier 990–20 24.5236.4211.125.325.726.727.7210.07.10.00.01.322.024.123.222.01.0213.321.32.40.027.623.529.124.65.622.223.220.728.225.3 1 0 9 9 9070605001894651286639338384267 15 80–1 20.0.21.25.23.0.22.0.221.29.220.24.2.0.27.29.24.211.210.223.233.210.24.24.25.25.29.224.211.27.2. 0 9 2 1 h Marc 0 0.40.10.470.120.30.690.210.220.660.130.170.371.130.690.350.251.060.130.530.290.270.680.90.080.30.10.540.240.620.290.23 05 201 ^5^8^5^8^9^1^6^1^4^2^1^6^5^6^6^5^6^2^6^4^3^2^6^9^6^8^3^9^3^2^7 01 10.0.10.1.4.17.3.3.10. 2.7.29.16. 20.1.7. 2.10.17.1. 1.8.2.15.6. 1: n. 6.228.127] at 2 Himalayanregio 2erarea(km) 2000 ^410.50.4^110.70.09^4110.40.47^121.80.12^2750.29^6516.70.67^183.60.2^22.70.2^610.50.64^1420.13^171.90.17^367.80.35^1629.41.11^6916.50.69^3760.35^254.90.25^0520.51.06^131.30.15^527.50.52^314.30.3^313.40.3^7212.10.7^9619.40.89^0820.08^316.20.3^111.90.1^5990.56^2730.27^6213.40.61^345.60.32^287.10.27 1.19 Kush Glaci 990 ^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^1.^0.^0.^0.^1.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0.^0. 7 1 1179399382970225356241125821515 d by [ Hindu 11.11.1.5.17.3. 9. 1.7.317.6. 20.1.7.4.3.13.20.2.6.1.9.3.13.6.7. Downloade angeinthe 1980 ^11.10.8^1.10.23^11.90.82^20.22^5.50.54^17.91.31^40.37^30.4^12.40.35^2.20.07^2.40.1^8.10.16^29.30.88^17.10.48^6.70.05^5.50.19^21.20.52^1.70.03^8.50^5.50.64^5.10.57^14.71.32^211.67^2.30.13^6.90.68^1.90.23^10.20.82^4.10.46^15.20.92^6.60.63^7.30.49 h c amplesofglacier GLIMSID/Name G073222E37165NG073242E37192NG073276E37183NG073311E37179NG073296E37157NG073306E37138NG073355E37143NG073375E37154NG077760E35012NG077783E34999NG077770E34989NG077711E34982NG077724E34958NG077774E34919NG077792E34912NG077815E34923NG077865E34917NG077894E34926NG077910E34918NNuptseWestLhotseLhotseImjaEastAmadablamAmadablamDuwoBechungRaphstrengThorthormiLuggeDrukchang x e e o. 1234567812345678901123456712345 v N 11 ati ent or s d ble2.Repre sin WakhanCorri ShyokBasin ImjaValley Lunanaarea Ta Ba A. B. C. D. 10 S.R. Bajracharya et al. inventorieswaschallengingandmostlybasedonexistingtopographicmaps.Overthepast severalyears,remotesensing–basedinventoriesforseveralpartsoftheHKHregionhave been entered into the GLIMS database (Raup et al., 2007). However, different methods and data sources have been used (topographic maps based on aerial photos with limited fieldinputs,satelliteimages),withacquisitiondatesthatareyearstodecadesapart.This underlinestheneedforahomogeneousmethodfromasinglesourceofdatausingrecent imagery acquired within ashort time span. The changes in glaciers can be assessed from time series of images. The selected basins cover a representative range of climates and glacier systems (Figure 2). A time seriesanalysiswasperformedusingahomogeneoussourceofimages(Figure5,Table2) toassessthe glacierchange. Aslightreductioninglacierextentwasobservedconsistentlyinallglaciertonguesin the Wakhan Corridor (Figure 5, panel A). The glaciers in the Shyok Basin in the Karakorum showed a different pattern, with glaciers advancing and tributaries merging, especiallyduringthelastdecade,consistentwithearlierreports(Archer&Fowler,2004; 5 1 Hewitt, 2005, 2011; Scherler et al., 2011; Tahir et al., 2011). Glaciers in the Himalayas 0 h 2 (Figure5,panelsCandD)showedconsistentretreatinbothNepalandBhutan.Someice- rc apron glaciers have disappeared from the mountain slopes, and glaciers are increasingly a M fragmented. These glaciers are all characterized by synchronous ablation and 05 accumulation during the monsoon season and are particularly sensitive to climate 1 perturbations(Immerzeel,VanBeek,Konz,Shrestha,&Bierkens,2012).TheImjaLake 0 1: inNepal(Figure5,panelC)isoneofthefastest-growinglakesintheHimalayas,andthe 2 at DC glacier that connects to the lake has retreated much faster than other nearby DC 7] glaciers (Bajracharya et al., 2007). The same phenomenon was observed in the DC 2 1 glaciers that connect to the Raphstreng, Thorthormi and Luggye glacial lakes in the 8. 2 Lunana region inBhutan (Figure5, panel D). 2 6. Thedistributionofindividualglaciersisimportant,assmallglaciers(Glacier2inthe 9 1 WakhanCorridor,Glacier10intheShyokBasin,WestLhotseGlacierintheImjaValley, 1. 7 and Rapthstreng Glacier in the Lunana area) are more sensitive to climate change than [ by largeglaciers(Bahr,Meier,&Peckham,1997).Alargeproportionofthetotaliceareain d theGangesandBrahmaputraBasinsiscontributedbysmallglaciers.Thedistributionof e d a thetotaliceareaoverdifferentelevationbandsisanothercrucialdeterminantforclimate o nl change sensitivity. w o WesuggestthatintheHinduKushglaciersareretreatingslowlybutsteadily,whilein D the Karakoram glaciers show a mixed response, varying from thinning of large DC tongues to advancing and surging tributaries. In the Himalayas, glaciers are retreating rapidly,withamarkedcatalyticroleplayedbyglaciallakes.However,acompleteregional understanding will require multi-temporal comprehensive glacier inventories in combination with high-resolution climate datasets. Conclusions A large step has been taken in compiling a reference cryospheric dataset for the entire HKH region which is publicly available and can be used as a benchmark against which changes can be assessed. The challenge now is to maintain this dataset and to further extenditbyincreasingthetemporalintervalasfarbackintothepastasavailableimagery allows. Largerglaciers(exceeding15km2inShyokandtheWakhanCorridorhaveshownno significantchangeinarea;however,thesmallerglaciersareretreatingfaster.Theglaciers