Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ). 1 − ), the + 39 m from 0.3 % yr ± − 30.8 m 4 − , and W. F. Manley total glacierized area in Nepal (Tamor 3 2 3950 3949 88 km ), with enhanced thinning rates in the upper part 1 ± − 2 0.9 % from 2000 to 2006) compared to the previous , M. Williams ± 1 1,2 − 0.9 m yr 0.16 % from 1962 to 2000). Retreat rates of clean glaciers ± ± from the 1960’s to the 2010’s, with a higher rate of retreat in 1 1 − − 0.8 m 0.43 % yr to be located in Sikkim. Supraglacial debris covered 11 % of the total − − , Y. Arnaud , almost double than those of debris-covered glaciers ( 2 1 1 − 0.20 % yr 0.08 % yr 34 km − ± ± 0.7 % yr 2 − 2000; (2) changes in glacier area (1962–2006) and their dependence on topo- 0.24 % This discussion paper is/has beenPlease under refer review to for the the corresponding journal final The paper Cryosphere in (TC). TC if available. Laboratoire de Glaciologie et Géophysique de l’Environnement, 54, rueLaboratoire Molière, d’étude Domaine des Transferts en Hydrologie et Environnement, BP 53Department 38401, of Saint Geography and Institute of Arctic and AlpineInstitute Research, of University Arctic of and Alpine Research, University of Colorado, Boulder, CO, 80309, USA − the last decade ( decades ( were Debris-covered tongues experienced1960’s to an 2000’s average ( of lowering the of debris covered area, and overall thickening at the glacier termini. Landsat/ASTER yielded 1463 km basin) and Sikkim (Zemu569 km basin), parts ofglacierized Bhutan area, and and China,area. supraglacial of which lakes Based we covered on estimated about analysis 5.8 % of of high-resolution the imagery, debris-covered we estimated an area loss of Advanced Spaceborne Thermal EmissionWorldView-2 Radiometer (WV2) (ASTER), QuickBird sensors. (QB)ters We and based present: on∼ a (1) new spatial “reference” patternsgraphic geospatial variables of Landsat/ASTER (elevation, glacier glacier slope,variables inventory aspect, parame- (solar percent from radiation debrisand and cover) (3) as precipitation), changes well extractedship in as on to glacier climate surface a elevations temperature for glacier-by-glacier extracted debris-covered from basis ASTER tongues data. and Glacier their mapping relation- from 2000 This study presentsmonsoon-influenced spatial part patterns ofspatial in the scales. glacier Himalaya We arearemote-sensing combined (eastern and data Corona Nepal from elevation KH4 Landsat and changes 7 and in Sikkim) Enhanced topographic the at Thematic data Mapper multiple with Plus more (ETM recent Abstract The Cryosphere Discuss., 8, 3949–3998,www.the-cryosphere-discuss.net/8/3949/2014/ 2014 doi:10.5194/tcd-8-3949-2014 © Author(s) 2014. CC Attribution 3.0 License. 1 Universitaire, BP 962 38402, Saint Martin d’Hères cedex, France Martin d’Hères cedex,3 France Colorado, Boulder, CO4 80309, USA Received: 2 April 2014 – Accepted: 15Correspondence April to: 2014 A. – Racoviteanu Published: ([email protected]) 18 JulyPublished 2014 by Copernicus Publications on behalf of the European Geosciences Union. Spatial patterns in glacier areaelevation and changes from 1962 tothe 2006 monsoon-influenced in eastern Himalaya A. Racoviteanu 5 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ), the Advanced + erential ablation on ff er et al., 2014) provides ff 3952 3951 coupled with ASTER imagery, and extracted glacier parame- + While some theoretical understanding of the climate–glacier relationship at to ASTER-derived surface temperature andpixel debris basis. cover In characteristics previous on studies,illustrated a Sakai the pixel-by- et importance al. of (1998,tures supraglacial 2002) (ice surface and walls, temperature Fujita ablation as cones, andthe supraglacial well Sakai surface lakes) (2014) as for of surface inducing the fea- remote di debris-covered sensing techniques tongues. to Hereas investigate we a the step complement spatial towards these variability inferring its of studies thermal supraglacial with characteristics. debris, tion changes over almost five decades basedKH4 on and high-resolution 2006 datasets QB/WV (1962 data), Corona andlar investigated them emphasis using was statistical placed analysis. on AFor particu- the a behavior of subset clean of glaciers(1960s the vs. to debris-covered debris-covered 2000) glaciers. on tongues, the we basis computed of glacier topographic maps elevation and changes recent DEMs and related them advance our understanding ofthat the govern climatic, glacier topographic fluctuations andtial across glaciological patterns the parameters in Himalaya. glacierfrom In area Corona KH4, this and Landsat elevation study, 7 we changesSpaceborne Enhanced Thematic using Thermal evaluate Mapper Emission spa- multi-temporal Plus Radiometer satellite (ETM (ASTER),2 data QuickBird (WV2) (QB) sensors. and We constructed WorldView- aon new 2000 “reference” geospatial Landsat glacier ETM inventoryters based on a glacier-by-glacier basis. We evaluated spatial trends in glacier area and eleva- develop baseline glacier datasets,Nepal Himalaya such (Bolch as et al., in 2008a) the and parts Tien of Shana Sikkim (Narama mountain-range Himalaya (Raj scale et et is al., al., startingGardelle 2013). to et 2007), emerge al., 2013), (Scherler updated, et accurate al., glacier 2011; inventories are Bolch continuously et needed al., to 2012; classified Corona imagery from the 1960’s and 1970’s has increasingly been used to available, but their accuracy is not known with certainty. Given these limitations, de- glacier mapping in thisdue area to is unsuitable gain limited settingssatellite by image and frequent acquisition. the Furthermore, cloud persistence this cover area ofdata has and seasonal very needed snow, limited sensor for which baseline saturation comparison topographic hampers withBhambri recent and satellite-based Bolch data, (2009a). assurveys discussed The conducted in earliest by detail Indian expeditions in these glacier are in maps limited the to date a mid-nineteenthon from few century glaciers. topographic Survey The (Mason, Geologic of 1954), Survey IndiaFor of but eastern India maps (GSI) Nepal, (Sangewar inventory 1970’s based and topographic maps Shukla, from 2009) Survey is of India not 1 in : 63 the 000 scale public are domain. of the Himalaya (Bhambri etin al., the 2011; eastern Kamp Himalaya et (Bahuguna,2011; al., 2001; 2011; Basnett Krishna, Frey et et 2005; al., al.,eastern Bajracharya 2012), extremity 2013). and of and Nepal, Shrestha, Parts a Sikkim few and ofglacier Bhutan) the still data lack monsoon-influenced comprehensive, multi-temporal needed eastern for Himalaya accurate (the change detection. The use of remote sensing for jracharya et al., 2007;et Bolch, al., 2011), 2007; glacier lake Bolch changeset et (Wessels et al., al., al., 2002; 2008b; 2008a; Bajracharya Gardelle et Bhambriet al., et et al., 2007; Bolch al., al., 2007; 2010; 2011) Bolchcant Kamp and gaps et do region-wide al., remain. The glacier 2011; newa mass Kääb global global Randolph et balance inventory dataset al., (Berthier (Pfe ofthe 2012; glacier quality Gardelle varies outlines et and intended the al.,glacier for outlines parameters. 2013), large-scale Among may but recent not studies; glacier be signifi- in inventories, suitable we some for cite detailed regions those regional in the analysis western of part Himalayan glaciers have aroused a lotrespect of to concern glacier in area the and lastwater elevation few cycle years, changes (Immerzeel particularly and et with al., their 2010, consequencesRemote 2012; for Kaser sensing the et regional techniques al., 2010; helped Racoviteanu et improve al., estimates 2013). of glacier area changes (Ba- 1 Introduction 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and N to + 00 52 0 04 ◦ separation angle), ◦ cult due to the heavy C, with an average of ◦ ffi C and 19.8 ◦ E longitude), located on either side 00 50 0 55 ◦ 3954 3953 E to 88 00 57 0 00 ◦ N latitude and 88 00 26 0 C based on the same observation record (IMD, 1980). ◦ 08 ◦ We defined a non-metric camera model in ERDAS Leica Photogrammetric Suite (1) Corona KH4 scenes (year 1962) were obtained from the US Geological Survey declassified documentation of the KH4 missionblock (Dashora adjustment et procedure al., 2007). was The used LPS to bundle estimate the orientation of all the CORONA significant geometric distortions due cross-pathFrame panoramic Ephemeris scanning. Furthermore, Camera the and(roll, Orbital pitch, Data yaw, (FECOD) speed, camera/spacecraft altitude,missions, azimuth, parameters needed sun to angle construct and a filmavailable. camera scanning Orthorectification model rate) and of for to Corona Corona correctdistortions, scenes these so is distortions here notoriously are we not di describe in detail the methodology(LPS), used. with parameters (focal length, air photo scale, flight altitude) extracted from the of the Himalaya), suitableat for 7 glaciologic microns purposes. by Sixported USGS Corona for from stripes the the KH4 were original mission scanned actual film is pixel 7.62 strips. m size The (Dashora of et nominal approximatelyolution. al., ground 2 2007); Raw, resolution m unprocessed however, we re- using Corona calculated the images an scale obtained of from the USGS photos are known and to the contain scan res- Remote sensing datasets used in(1) this baseline study remote are sensing summarizedagery data in (year for Table 1, 1962); the and (2) 1960’s included: ASTER “reference” decade and datasets from (3) for Corona 2006/09 2000 high-resolution declassified imagery decade im- from from QB Landsat and ETM WV, allEROS described Data below. Center (USGS-EROS 1996).two The panoramic Corona cameras KH4 (forward-looking system andand was equipped rear-looking acquired with with imagery 30 fromWe February chose 1962 images to from December the 1963 end (Dashora of et the ablation al., season 2007). (October/November in this part 3.1 Data sources 3.1.1 Satellite imagery 3 Methodology This climatic particularity causesaccumulation and a ablation occurring “summer-accumulation” simultaneously in glacier1984). the regime In summer (Ageta Sikkim, type, and rainfall Higuchi, with amounts rangeerages from of 500 3580 to mm 5000 recorded mmand at per 164 Gangtok year, with rainy station annual days (1812 av- m) pertemperatures (1951 year at to (Nandy this 1980) et station (IMD, al., 1980), 15.5 were 2006). reported Mean as minimum and 11.3 maximum daily Asian summer monsoon circulation system (Bhattinflow and of Nakamura, moist 2005) air caused from by the(Yanai the et Bay of al., Bengal 1992; to Benn theacts Indian and subcontinent as Owen, during 1998). a the The summer barriersouth Himalaya slopes to and of Tibetan the the plateau monsoon Himalaya (HTP) during winds, the bringing summer about months (May 77 to % September) of (Fig. precipitation 2). on the glaciers cover about 68 %the of remaining the are glacierized cirquearea area, glaciers mountain is and aprons glaciers typically (Mool cover coveredslopes et 28 by %, (Mool al., heavy and et 2002). debris-cover al., The originatingtermini 2002), glacier from reaching (Kayastha ablation rockfall up et on to al.,province the a 2000). of thickness steep India, The of mapped several easternShukla, in meters 2009). part 1970 at The of by the western part Survey glacier thismor is of area and located India in Arun constitutes (Shanker, eastern basins. 2001; the Nepal, Climatically, this and Sangewar Sikkim area encompasses and of the the Ta- Himalaya is dominated by the South The study area28 encompasses glaciersof the border in between Nepal the andRelief India in in eastern the Ganges this Himalaya and area Brahmaputra (27 basins (Fig. ranges 1). from 300 m to 8598 m (Mt. Kanchenjunga). Long valley 2 Study area 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , and scene 2 + ects of topographic ) of the bundle block ff y 10 m. The GCPs were obtained in the field ± 3956 3955 scene from December 2000, obtained from the + 60 m. This is consistent with accuracies obtained on ∼ image (15 m spatial resolution). GCPs and were identified on the Landsat cients (RPCs) provided by Digital Globe, using an SRTM DEM, and mo- ffi + of the Corona images of y (3) Two QB scenes from January 2006 were obtained from Digital Globe as ortho- (2) The orthorectified Landsat ETM scale Indian topographic mapsborder at (Srikantia, this 2000; scale Survey_of_India, are 2005). restricted within 100 km of the Indian in several studies (Berthiervertical et accuracy al., 2006; in Fujitarespect our to et study 25 al., field-based area, 2008; GCPson calculated was Gardelle 31m non-glacierized et as terrain al., root 2012).a including mean Trimble Its roads Geoexplorer square XE and (RMSEz) series.compiled bare with (2) from land Survey The of Swiss outside IndiaFoundation topographic the maps for map Alpine from glaciers (1 Research the : using was 150 1960sThe 000 used to exact scale), to date 1970s, extract of published 1960’s each by glacier quadrant the is elevation Swiss not contours. known with certainty because the original large- 3.1.2 Elevation datasets Two elevation datasets wereSRTM used DEM in (90 this mparameters study: spatial for resolution) (1) the 2000 (CGIAR-CSI the decade. The 2004) hydrologically-sound SRTM CGIAR was accuracy and used biases have to been extract quantified glacier scenes in ERDAS Imagine Leicamial Photogrammetry Coe Suite (LPS) usingsaicked Rational them Polyno- in ERDAS Imagine.the The orthorectification scenes process were using resampled the toand cubic 3 m-pixel convolution processing method size to during time. reduce50 One disk cm space spatial WorldView-2 resolution from (WV2) 2of December panchromatic, 2010 Zemu was ortho-ready also glacier, obtained which scene toto cover was the at UTM missing terminus projection from zone the 45N, with QB elevations extent. referenced All to datasets WGS84 datum. were registered surface temperature trends over debris covered tongues. ready standard imagery (radiometricallyform calibrated distortions) and (Digital_Globe, corrected 2007). for Thesewere sensor scenes well-contrasted and cover and an plat- area mostly of snow-free 1107 km outside glaciers. We orthorectified these Williams, 2012) and another ASTER scene from October 2002 was used to investigate tained at no cost through(Raup the et Global al., Land 2007). Ice(15 m Monitoring The spatial from ASTER resolution), Space scenes 3 (GLIMS)mal have channels project channels at 3 in 90 the m, channels a short-wave inselected swath infrared width at the of at the 60 visible end 30 km m, of and wavelengths andThe the a revisit ablation four ASTER time season ther- of scenes for 16 minimal were days. snow,in Images used and were challenging had to little areas complement or where the noaddition, shadows clouds. Landsat-based the or glacier surface clouds kinetic delineation obstructed temperatureNovember product the 2001 (AST08) view from was of an used the ASTER in glaciers. scene In from a debris cover delineation algorithm (Racoviteanu and USGS Eros Data Centerhas was seven used spectral as channels “reference” at dataset.a 30 The m panchromatic spatial Landsat channel resolution, ETM a(185 at km). thermal 15 channel In m, at addition, a 60 m six revisit and orthorectified time ASTER of scenes 16 from days 2000 and to a 2005 large were swath ob- width (SRTM) DEM v.4 (CGIAR-CSIterrain 2004) displacements. and The were Corona used stripesthe to were final mosaicked correct orthorectified in e image. ERDAS The LPSadjustment horizontal to process was produce accuracy 10.5 (RMSEx, m. Ancheck independent analysis points of chosen location independently accuracy using ofSEx, 30 the initial GCPs yieldedCorona an images actual in “ground” Mexico, using RM- ader, fitting personal software communication, and 2011). the FECOD parameters (H. Sny- ground control points (GCPs) extractedsat from the ETM panchromatic band ofimage the on 2000 Land- non-glacierized terraineas. including Tie moraines, points river (TPs) crossings, were andLandsat digitized image. outwash from Elevations ar- one were Corona extracted strip from to the another Shuttle as Radar well Topography as Mission on the stripes simultaneously, and model parameters were calculated on the basis of 117 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | includes ). There is 1 − erences in pre- ff 1.07), and a majority > 5), the NDSI glacier map Spatial domain 1 / snow/ice) based on visual = versus 805 mm yr 1 200 − 4 and 3 5 km. Given the well-known biases > / ∼ , or ) (Table 3). ◦ 1 − 3958 3957 5 median filter was used to partially remove remaining noise, as is a subset of spatial domain 1, and comprises 50 glaciers from × snow/ice). The NDSI algorithm relies on the high reflectivity of snow = erence Snow Index (NDSI) (Hall et al., 1995), with a threshold of 0.7 ff 7 to remove noise. Debris-covered tongues for this dataset were delineated × 0.7 > 5 median filter was used here as well to remove remaining noise, and a few ar- × 4, then isodata clustering with a threshold of 1.07 (snow/ice For the 2006/09 QB/WV2 images, ice masses were delineated using band ratios For the 2000’s Landsat/ASTER inventory, glaciers were delineated using the Nor- Spatial domain 2 This spatial domain was split into four sub-regions on the basis of east-west and / manually on the basis of supraglacial features (lakes and ice walls) visible on the high part of the image.manually Some removed from transient the snow glacier persisting outlinesDebris-covered on in glacier the the basis tongues of deep were the shadowed delineated 1960’ssurface valleys topographic using kinetic map. was multispectral temperature data and (bandcombined ratios, texture) with from and topographic the variablesand 27 in Williams November a (2012). 2001 decision tree, ASTER described scene in Racoviteanu 3 filter of 7 2003). Compared to otherwas band cleaner ratios and (Landsat less 3 A noisy 5 and was thereforeeas preferred were (Racoviteanu adjusted et manuallymisclassified on al., as the 2008b). basis snow/ice, of and the some ASTER glaciers images, underneath notably low frozen clouds lakes in the southern were applied subsequently on thedigitizing basis of in the areas Swiss of topographic poor mapof contrast using glaciers. or on-screen transient snow/clouds, which obstructed the view malized Di (NDSI and ice in thetheir visible low to reflectivity in near the infrared shortwave (VNIR) infrared (SWIR, wavelengths 1.4–2.5 (0.4–1.2 µm) µm), (Dozier, compared 1989; to Rees, For the 1960’s decade, glacierimagery outlines by were extracted thresholding frominterpretation. the the A panchromatic digital Corona 5 numbersshown (DN in other studies (Paul, 2007; Racoviteanu et al., 2008a). Manual corrections 3.3 Glacier delineation and analysis a more pronounced north-southprecipitation on gradient the China in side precipitation, (146 mm with yr theNepal lowest (Tamor amount basin) of andThese Sikkim glaciers (Zemu were basin), used cleanchanges for and as a their well dependence more on as climatic thoroughand and and analysis multiple topographic debris-covered. variables regression of using analysis correlations glacier for twoCorona area time imagery), and steps: and elevation the 2010’s 1960’s decade decade (represented (represented by by QB and WV2). tion, but only with characterizing thevalues. sub-regions TRMM in data our study integrated areacipitation over using patterns relative 10 years rainfall among (1998 the to(Table four 3). 2007) regions, and show The justifies di easternamounts our side choice than of of the spatial the western domains study side (Nepal) area (977 (Sikkim) mm yr receives higher precipitation north-south climate/topographic/political barriers,ages as from shown the Tropical in Rainfalland Measuring Fig. Nakamura, Mission 3. 2005; (TRMM) Bookhagen Rainfallsub-regions data climatically. and 2B31 The aver- dataset product Burbank, contains (Bhatt 2006) rainfallcontrol estimates are calibrated stations with used derived ground- tobank, from characterize 2006) local the with and ain global spatial the gauge resolution TRMM of stations data 0.4 et (Bookhagen (Bookhagen al., and and 2013), Burbank, here Bur- we 2006; are Andermann not et concerned al., with the 2011; absolute Palazzi values of gridded precipita- We defined two spatial domainsthe for Sikkim our province study of area India,of (Fig. eastern Bhutan 1). Nepal and (Tamor China and (Table 2). Arun basins), as well as parts 3.2 Analysis extents 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and 2 31 m) and ± in 2000 (14 % of the 3 %, respectively. Un- 2 ± 5 km ± 2 6 and ± 25 m). Sources of uncertainty are ± , with an average size of 3 km 2 3 %, ± erences in the north and south directions. ff 3960 3959 (Table 4a). Of the total glacierized area in spatial was covered by supraglacial debris (11 % of the 2 2 ), using the accuracies of the SRTM DEM ( erences and surface temperature was evaluated along 88 km z ff 10 km ± ± 2 2 (Table 4b). These values for glacier area appear small, but are 2 erences (1960–2000) over the debris covered tongues on a pixel- ff In 2000, glacier size ranged from 0.05–105 km Uncertainties of glacier outlines derived using the semi-automated methods for Glacier area changes (1962 to 2000) and their dependency on topographic and cli- For all inventories in spatial domain 1, ice masses were separated into glaciers on a median size of 0.9 km The northern side ofshadow, the with gentler divide slope is andsouthern part lower of slopes rates of the of erosion Tibetan thePrecambrian because plateau, Himalaya of crystalline situated the are rocks in dry steep, (Mool aand climate. comprise et The monsoon rock al., of fall 2002). soft due Theseexplain sedimentary the to slopes high rocks large are amount and prone of amounts debrisThe to of on behavior erosion moisture the glacier of brought surface debris onpatterns by the is the covered south explored monsoon, side vs. in of more which clean the detail may divide. glaciers in Sect. in 4.3 relation below. to topographic/climatic four regions in spatial domainIn 1 Sikkim, displays supraglacial di debrisglacierized covered area), an in area contrast of with 78kmglacierized the area). northern The side of prevalencecan the of be Himalaya debris explained (China, cover 2 in % on part of the by the the south geology side and of topographic the patterns Himalaya in the two regions. 4.1 The Landsat/ASTER 2000 glacier patternsThe (Spatial domain 2000 1) glacierwhich inventory 162 based were oncovering situated Landsat an area in and of Nepal, 1463 ASTER km domain 186 yielded 1, in 487 a total Sikkim, glaciers ofglacierized 30 (of 160km area). in Of Bhutan thesome and percent 487 of 109 debris glaciers in cover in on China), their this tongues. The spatial debris domain, cover distribution 68 among the glaciers (13 %) had the error in the digitizationdiscussed of in the detail topographic in map Sect. ( 5.4. 4 Results root mean square error (RMSE certainties in elevation changes of the debris covered tongues were calculated as the DEM. Elevation contours werelated digitized using from the the TopoGrid topographicputed algorithm map elevation in di and ArcGIS, were usingby-pixel interpo- a basis and 90 examined m their pixel spatial patterns.from size. ASTER-based the We surface 2002 temperatures then ASTER com- imagelationship were between extracted elevation for di each debris-coverlongitudinal tongue, transects and on the a re- pixel-by-pixel basis for the selected glaciers. Corona, Landsat/ASTER and Quickbird were Khalsa, 2007; Racoviteanu et al., 2009). matic variables were calculated ontial a domain glacier-by-glacier 2. basis Elevation for changes theglacier (1960 50 tongues to glaciers from 2000) in 1960 were spa- to calculated 2000 for on 21 the debris-covered basis of the topographic map and the SRTM extracted on aness glacier-by-glacier were basis calculated using from massFarinotti zonal turnover (2011), functions. principles based and Average on ice the glacieroutlines flow approach and mechanics thick- of the Huss SRTM Farinotti and DEM (2009).flow to Their law derive method and thickness a uses estimates shape glacier iteratively factor basedanalysis, (Paterson, on 1994). we Glenn’s For assumed simplicity and no consistencycluded shift for all change in nunataks and the snow-freeBodies ice steep of divides rock ice over walls the from above the period the glacier bergschrund of area analysis, were calculations. and considered ex- part of the glacier (Raup and with texture analysis. the basis of theManley SRTM (2008), DEM, described in using Racoviteanu hydrologic et al.maximum functions (2009). elevation, in Glacier median area, an terminus elevation, algorithm elevation, average developed slope by angle and average aspect were resolution images. We also mapped supraglacial lakes based on band ratios validated 5 5 20 25 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ◦ < , or 2 400 m + 5 km ± from 1989/90 1 88.9 − − ) compared to the 1 700 m and . The prevalence of − + 2 , with a positive skew ◦ 100 km 0.9 % yr ± > 1 − erences among the four regions ff ). Our rates of change are within the 1 − 0.17 %) for the last 38 years. In a recent 8.4), showing that glaciers with area ± = 0.43%yr 1 − − 3962 3961 0.16%yr ± ) from 1962 to 2006 for the 50 glaciers (Table 5), erences in rock outcrops specific to each dataset, 1 ff − 0.36%yr − 0.20 − 0.08 % yr erences seem to be consistent with general air circulation pat- ± ff 5 km in 30 years for this glacier. Glacier thickness ranged from 1 − ∼ (Racoviteanu et al., 2008a). The frequency histogram of glacier area 2 50 m) compared to the eastern side (Sikkim). This may be explained + 0.38) (Fig. 4b) and no significant di 0.24%yr 1 km = − ∼ are predominant, and glacier size decreases non-linearly. The long right-tail 2 (SW), whereas glaciers of Sikkim for example had an average orientation of 131 0.05) (Table 4b). Glacier length ranged from 0.08 km to 23 km (Zemu glacier), with ◦ The average slope of glaciers in spatial domain 1 was 23 Glacier termini elevations in spatial domain 1 ranged from 3990 m to 5777 m, with 10.3 % ( 13.5 % of the glacierized area ( p > study, Basnett et al. (2013) reportedto a 2010 glacier area based change on of 0.16 analysis % yr of a few selected glaciers in Sikkim, which is about 20 % To minimize uncertainties due towe di used the same− rock outcrops forwith each double dataset. the rates Weprevious from obtained period 2000 1962 an to to area 2000 2006range ( change ( of of those reported inestimates. other For studies, example, if for we Sikkim, consider our− the study uncertainties yielded in an the area change loss of 4.2 Glacier area changes 1962–2006 (spatialOut domain of 2) the 487 glaciersin in Nepal spatial and domain 1,changes Zemu from a basin 1962 sample (Corona in of imagery) 50 Sikkim to glaciers 2000 (spatial (Landsat/ASTER) from and Tamor domain 2006 basin (Quickbird). 2) were used for deriving area quency distribution of both lengthindicating and thickness the were prevalence positively skewed ofaspect with shows short, long two tails, predominant shallow orientations valley-typeNW) of the and glaciers, glacier east-northeast respectively. tongues: Glacier west-northwest (E-NE)237 (W- (Fig. 5). Glaciers in(SE). Nepal In a had previous an inventory,of average Mool glaciers aspect et al. of (south, (2002) southwest,western attributed southeast slopes, the and which predominant prevent east) orientation glacier to growth the compared to higher the temperatures colder on eastern the slopes. an average of 2 kmin (Fig. 4c). 1970’s, Mool and (2002) the28 reported km Geologic a for Survey length the of ofcrease 26 same India km in for glacier (Sangewar length Zemu and based glacier of 3 Shukla, m on to 2009) 1970 144 m, reported topographic with the maps. highest frequency This for thickness suggests less a than 30 de- m (Fig. 4d). The fre- ( (skewness west, with glacier terminidivide and median (China) elevations compared muchrespectively). to higher These on the di northern southern sideterns side of in the the (Nepal/Sikkim) area, where ( thetion on Asian the summer southern monsoon slopes brings of largeIn the amounts contrast, Himalaya, of favoring the precipita- glacier upper growthmate at reaches lower due of elevations. to the valleys the2008), and monsoon causing the being glaciers Tibetan to blocked plateau be by have found the at a topographic higher drier barrier elevations. cli- (Clift and Plumb, to drier climate inglacier the elevations, former. with In higher our glacier studyside minimum area, (Nepal) and we ( median note elevations aby on slight the the east-west western location gradient of in the monsoon. glaciers The on north–south the gradient in western glacier side elevations is of stronger the than the topographic east– divide, away from as we noted in2008a). the Cordillera Blanca of Peru in aan previous study average of (Racoviteanu et 4908 m;a al., median mean glacier of elevation 5702proximation m ranged of (Table from glacier 4b). 4515 equilibrium m Considering lineBenn to glacier altitude and (ELA), 6388 median m, Owen our elevation (2005), with results asHimalaya who are (6000–6200 documented in a m) agreement higher compared coarse with ELA’s to ap- on ELA’s the the southern northern slopes slopes (4600–5600 m), of due the size was (Fig. 4a) is skewed10 km to the rightextremes (skewness represent onlysmall a glaciers few is glaciers a with pattern an faily area common in inventories which include small glaciers, about three times larger than tropical glaciers for example, where the average glacier 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ), steep (aver- in the last four in the Khumbu 2 1 1 erences in area − − ff test for variances) 1 km F ) from 1962 to 2006 C yr 1 erence in mean rates ◦ < − ff was reported by Kulka- 1 0.25 % yr 0.17% in the last four de- − − ± 1 − 0.56 % yr − 0.7 % yr − 0.1) (Table 6). The strongest (negative) 0.36%yr − 6 % of glacier area on average), and have 0.05), i.e. glaciers with larger parts of their p < < 3964 3963 0.05). p < < erent climatic area, the Cordillera Blanca of Peru ff value p test ( erences between the debris-covered and clean glaciers sam- ect of debris cover on glaciers above a certain “critical” debris F ff ff ), have little debris cover ( ◦ 64 % of their area, with a mean of 25 % ( − erences in area changes. Statistical analysis (two sample ff 50 % area loss) for several glaciers in the northern and southern parts of the study Topographic parameters of debris-covered vs. clean glaciers may explain some of Correlation analysis suggests a greater glacier area loss for south-facing slope Correlations between topographic/climatic parameters and area change for the 50 0.7 % to > ples in terms of glacier area, area change, minimum elevation, altitudinal range and spread and a highercovered glaciers. percentage Between 1962 of and areawith 2006, loss clean a glaciers mean of lost of clean 3.4area, 32.6 to with glaciers %, 64 a % compared while mean of of debris-covered to theirof 14.3 glaciers % area debris- area on lost change a between only glacier-by-glacier clean basis.based 0.7 % The and on di debris two-sample to covered 61 % glaciers was of statistically their significant these di showed significant di significant at 95 % confidencearea interval covered ( by debrispotential experienced insulating less e area loss.thickness This (Mihalcea et is al., tochanges 2008; be between Zhang expected clean et given and al., the debris 2011). covered There glaciers. were Figure 7a di and b shows a larger age slope of 25 termini elevations of 4423 to 5500 m. aspects. Furthermore, smallera glaciers smaller altitudinal situated range exhibited at largersistent rates with lower of area observations maximum change. from These(Racoviteanu elevations, results a et are with al., di con- 2008a), indicating consistenttionship patterns between in the debris glacier behavior. cover The percent rela- of glacier area and area loss was statistically weakly correlated to area change− (Table 6). On a glacier-by-glacier(Fig. basis, 6). glaciers lost Spatial patterns( of these areaarea. changes A closer (Fig. look 6) at these show glaciers largest showed that area they changes are small ( diation and minimum elevations were not statistically significant, and they were only indicating larger area changes foraltitudinal glaciers situated range. on In lower contrast, summits, and glacier with location a (latitude small and longitude), slope, solar ra- decreasing trend in precipitation. However,the given glacier the termini, location these of data the are station not well conclusive. below glaciers in spatial domain 2median indicate elevation, that glacier glacier maximumcorrelated area, elevation, with percent altitudinal range, the debrissignificant percent cover, at aspect area the change 90 and %correlation from precipitation confidence interval, with 1962 were area to change 2006 was (correlation found for statistically maximum elevation and altitudinal range, sensitive to climatic changes givenmay their provide location enough in precipitation aet monsoon-influenced to al. area, high (2013) which altitudes examined annual tofound climate that maintain records mean accumulation. from annual Basnett temperatures the increaseddecades, Gangtok at station with a (1812 most rate m), warming of and 0.04 observed during the winter, and a slight, non-significant 5.1 Topographic factors controlling glacier areaThe change area change resultscaades) presented point above ( tothe rates Himalaya. of For example, retreatrni an that et area al. are change (2007)such half as of for Alps the the (Kääb et ones western(Racoviteanu al., et Himalaya reported 2002), al., the and 2008a). in Tien in We Shan other speculate (Bolch, other that 2007) parts glacierized eastern and the Himalaya mountain of glaciers Peruvian ranges Andes may be less elsewhere in the eastern Himalaya byregion Bolch of et al. Nepal (2008a) from ( 1962 to 2001), using similar methodology and data5 sources. Discussion lower than our estimate. The Basnett et al. rates are also lower than the ones reported 5 5 25 20 10 15 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 2 ± − 12 km 30.8 − ∼ 0.13 yr ± 0.5 − 10 times smaller (2 km ∼ ), they have higher termini elevations 2 ), which are similar to annual rates re- 1 − 3966 3965 ) for the period 2000–2011. Our rates are 1 − 0.9 m yr ± 150 m, which are observed towards the rock walls in 0.13 yr > 0.8m ± erence in thinning/thickening patterns, we extracted sur- ff − 0.81 − erences from 1960 to 2000 on a pixel-by-pixel basis (Fig. 10). ff 650 m to 1.3 km respectively from 1962 to 2006, with visible growth ) (Gardelle et al., 2013). We obtained higher thinning rates for glaciers ∼ 1 − 0.05) (Table 7). Clean glaciers in this area are 0.16 yr p < erences in the mid-upper zone of the ablation area of debris-covered tongues, ± ff 1.5 km from 1962 to 2006), and a glacier outlet is now clearly visible. The terminus 100 m in 44 years), in spite of increase in the area of supraglacial lakes. 535 m), and an elevation range about 3 times smaller than debris-covered glaciers We found that debris-covered tongues experienced an average lowering of In Figs. 8 and 9 we illustrate a few of these changes in more detail, using high 0.33 ∼ ∼ + a general trends, weupwards, note indicating higher a surface thicker temperatures debris from which insulates the the terminus ice to underneath, then temper- topographic map in these areas. 5.3 Supraglacial surface temperature patterns To explain some of theseface di temperature along longitudinalHere transect we for are atemperature presenting few patterns glaciers, one as derived of shown fromdisplay the in a 2002 glaciers, Fig. large ASTER Zemu 10. variability, imagery glacier particularly for (“B” for Zemu the in glacier 10 Fig. km (Fig. 10). towards 11) the Surface glacier terminus. As bris in the mid-lower partto of a the debris-covered thickening area, wave whichor that we mass speculate is balance might reaching measurements be the due inthat glacier this high terminus. area, rates we Due of cannot tothe assert thinning the upper, this. steep of lack Here parts of we of velocity consider the debris-covered area, are most likely due to errors in the lower than surface lowering− in the ablation zonesin of contact glacier with further a(“A” west growing in (Karakoram, pro-glacial Fig. lake, 10). such Otherthe elevation as glaciers changes, with S. such less as Lonak distinct Zemu spatialtion glacier patterns. (“B” di discussed In on Fig. above 10 Fig. we 10)and note larger display generally eleva- heterogeneity thickening in towardsKanchenjunga the glacier (“D”). terminus, The for latter example shows Yalung an glacier interesting (“C”) pattern and of “bulging” of de- evaluate elevation di 39 m from 1960’s toported 2000 in ( Gardelle etand al. Hengdun (2013) Shan, in the same climatic zone (Bhutan, glacierized area on a glacier by glacier basis). We chose these 21 glacier tongues to main 2, 21 glaciers had debris cover in their ablation zones (an average of 21 % of the 5.2 Glacier elevation changes for debris-coveredGiven tongues that 1960–2000 some oftion the remains whether glaciers some investigated ofning/thickening), here these and glaciers show are little what experiencing area may elevationsupra changes change, govern glacial (thin- the these lakes). ques- In changesthe this (for debris-covered area, example, tongues supraglacial in debris lakes 2006/09,the cover covered as only delineated or glaciers, from 5.8 for % QB/WV2 example of imagery.covered Some Zemu, the by of the area supraglacial of largest debris glacier in 2000. in Out this of area, the had 50 27 glaciers % analyzed of in its spatial area do- of the glacier inactive. 2006 In is contrast, uncertain, other since debris-coveredin glaciers some such the part as upper of the right the near-by part( Jongsang glacier of glacier terminus the may image be does in- not show significant rates of terminus retreat resolution Corona and QBsupra-glacier imagery. lake Figure on 8 S.Glaciers a Lonak on and glacier the b in upper showssome Sikkim, northern of the also part the rapid noted of ice growth in the underneathmore of Basnett image has uncertain, the are et collapsed, as most al. but pointed likelyadjacent the (2013). above. rock area glaciers A glaciers, changes (N. closer where are Lonak look lessminus and at retreated visible, S. and a Lonak) subset whichof area underwent (Fig. a mass 9) wasting. supraglacial shows Their( lake. two ter- Another branch of N. Lonak glacier has wasted significantly length ( on average) than debris-covered glaciers( (23 km (Table 7), which may all contribute to their higher rates of retreat. 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 5 % for re- < ects, resampling, image ff erences (thinning). There is 3 m for QB outlines), we ob- ff ± 60 m, with the largest errors were ∼ of 14 m globally (Digital_Globe, 2007). y , x ect our calculations of area change, since ff 3968 3967 0.05). An ordinary least-squared regression us- 6 m for Corona and 10 m. Geolocation errors on the ground were esti- p > ± ± erences in area. The geolocation accuracy of the stan- ff 1-pixel variability (Congalton, 1991). Recent glacier anal- 0.01). Standard residuals are close to normally distributed, ∼ = s, which in general accelerate ablation (Sakai, 2002; Fujita and 2 ff R erent paper (Racoviteanu and Williams, 2012), we found similar ff 30 m for Landsat/ASTER, ± scene, yielded an errormated of using a trendreference analysis Landsat on scene, the andconcentrated horizontal towards resulted the shifts in edges betweenconsider of Corona that the these and images, errors the minimally mostlythey a do outside not the impact glaciers. thedard We di QB scenes is estimated as RMSE The accuracy of“Perkal remote epsilon sensing band” glacier aroundet outlines al., glacier 2010), is outlines using often a (Racoviteanu estimated et al., using 2009; the Bolch mote sensing glacier outlines comparedwe to could high not resolution perform imagery.used In a as this validation study, source using( high-resolution imagery imagery, for since area thistained change. was a Instead, total using estimateHighest the of uncertainties 1-pixel image were variability classification associated errors with of the 3–6 larger % pixel for size our (Landsat). datasets. The The orthorectification process of the 1962 Corona, using GCPs from a Landsat ysis comparison experiments estimatedlines using the manually-derived accuracy outlines at of multipleet times automated al., and 2007; glacier various analysts Paul out- et (Raup al., 2013), and obtained a range of uncertainty of 2. 1. main types of errors, withwhich we an consider emphasis key on for classification glacier errors area and change estimates. conceptual errors, the definition of aclouds, glacier, and including internal mapping of rockvation ice all errors divides, described due mixed in pixels tohere, detail of inherent include in snow DEM errors Racoviteanu and uncertainty. et dueco-registration, Other spectral al. to mixing types (2009); atmospheric or of (4) raster and to ele- errors, topographic vector not conversion. e Instead, discussed we focus on the due to the algorithms used for glacier mapping); (3) conceptual errors associated with olocation errors, sensor limitations and ambiguityof in the the topographic satellite maps), signal, and/or (2) accuracy image classification errors (positional errors and/or errors Glacier outlines derived fromsemi-automated remote methods, sensing are data, known evenas to when discussed be using in subject well-established recent tocomes various studies an degrees (Racoviteanu important of et issue uncertainty, al.,sources in accumulate 2009; glacier at Paul change each et processing analysis,ing al., step. where data In 2013). errors this at This from study, various we be- variousand combined spatial data remote DEMs and sens- to temporal derive resolutionsmain glacier with sources parameters data of and uncertainty from here estimate topographic arise maps of from: area/elevation (1) changes. errors The inherent in the source data (ge- surface temperature ( with larger residuals inwalls), the discussed above. upper part of the debris5.4 covered tongues (close Uncertainty to estimates steep presence of thicker supraglacialtion debris. changes On and surface Fig.mentioned temperature 11, above, is where the we more relationship alsoless clear between note in variability larger eleva- the of elevation middle-upper di surfacethin debris temperature supra-glacial area debris than in theas this lower explanatory area. part, variable Regression probably forchanges analysis associated Zemu on using surface showed with surface temperature a temperature ( ing non-significant all 21 dependency debris-covered of tongues showed elevation a weak dependency of elevation changes on clean ice (middle of theferences ablation display a zone), high indicating variability, a withglacial thinner lakes spikes debris and of ice cover. large cli Elevation changes dif- Sakai, in 2014). areas In around supra- apatterns di of surface temperature increasing towards the glacier terminus, indicating the atures start decreasing from about 12 km from the glacier terminus to the limit with 5 5 10 15 25 20 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . , z 2 20km erences erences ff ff ± (1.4 %) of 2 2 4 of the contour / er only by 8.2 km ff erences in the rates of change in ff based on the same source imagery 2 3970 3969 of glacierized area for Sikkim in 2000 period erence in glacier numbers (186 glaciers in our ff 2 erences in glacier datasets due to rock inconsisten- 0.9 % from 2000 to 2006) compared to the previous ff 70 km ± 1 ± − 2 0.16% from 1962 to 2000). We speculate that some of this erent analysts, and were previously noted in other areas of ± . For simplicity, here we neglected the area change that might ff 2 % glacier area, inducing di 7 % from the inventory published by the Geological Survey of 1 1 − − ∼ ∼ in the glacier vertical changes were calculated using the RMSE 0.43%yr , or − 2 in 1960s based on the Swiss topographic map, which is 13 % higher 39 m. The errors associated with digitizing of the topographic map are ) (Table 8). These two area estimates di 2 ± 0.20%yr + 0.05 % yr − ± erence in spatial resolution of the imagery. Due to the short time period for approximately the same time period. We consider both the GSI and the ff 2 Elevation errors assuming an error ofinterval) and 25 m the for calculated error theof for 30.5m 1960’s SRTM topographic of 31 map m,considered (1 yielding smaller than an errors elevation change associated with the original map (Paul, 2003). (2000–2006), area uncertainties forchange. this time step might be larger than the area here we comply tofrom these guidelines. all For the consistency, we areathe removed calculations; glaciers; internal we we rocks included manuallyof “inactive” removed bodies a perennial of glacier. snowfields ice Uncertaintiesuncertainties from above in the embedded area bergschrund in change asamounted each part were to dataset, computed 3–6 % from asin of classification the internal the RMSE errors rocks glacierized of above, in area.puted each the and Uncertainties dataset with were related internal derived tofrom by rocks di each comparing specific datasets. area to The changescies di com- each amounted to dataset, vs.area “merged” of internal rocks be due to exposurearea of changes new computed from internal 1962 rocklast to due decade 2006 suggest to ( a glacier higherperiod ice rate ( of thinning. retreat The in glacier apparent the “accelerated” rate ofthe glacier di retreat in the last decade might be due to method is known toMcDonnel slightly (1998), so over-estimate we the consider our errorsconservative, overlal area described and accuracy in estimates accommodate to Burrough becertainty other and rather of errors debris-covered tongues, not GISglacier considered operations outlines, etc.). including here For some manually-adjusted (higher ofrors the by un- using debris-covered screen tongues, digitizing we in minimized streaming er- mode,Conceptual with errors a are high density relevanthow of here vertices. the in the glaciers contextconsensus were of on defined. how area these The change rules and glaciologic should relate community be to applied has (Racoviteanu come et al., to 2009), some and ers by 48.3 km 4. 3. ff of 706 km Swiss topographic map to overestimate the glacier area, potentially due to classifying Corona 1962 imagery for SikkimIn yielded 178 a glaciers with recent an publicationarea area of (Racoviteanu of 658km 742 et km al.,than 2014), our new we estimates reported basedestimates on 158 Corona more imagery glaciers from reliable with 1962.baseline than We an for consider the comparison the Corona with topographic moredi map, recent imagery. and Our we 1962 CoronaIndia use glacier (GSI) this inventory (Sangewar dataset and as Shukla, 2009), the which reported 449 glaciers with an area our estimated area. Thestudy significant compared di to 285which ice glaciers masses in were ICIMOD splitand and study) inconsistencies how are glaciers in most wereanalysis glacier counted. likely performed Methodology estimates due by di are to di the quite the world way common in (Racoviteanu in et multi-temporal al., image 2009). Similarly, for the 1962 decade, our analysis of 5.5 Comparison with other areas Comparison of our results tosistencies other and studies inaccuracies in in the this classificationour area methods of study used. Himalaya For estimated is example, in subjectbased 569km Sikkim, on to Landsat/ASTER incon- data (Sect. 4.1).reported For the 285 same time glaciers period, Mool(Landsat with et ETM al. an (2002) area of 577 km 5 5 25 20 10 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) in the 1 − ) followed 1 0.1 % from − for Sikkim in ± 1 2 39 m) on aver- 0.3 yr − − ) on a glacier-by- ± 1 0.06 % from 1962 − ± 1 − from the 1960’s to the 30.8m 0.43%yr − 1 − − 0.7 % yr 14.3 % or − − 0.2%yr − 0.08 % yr ± 34.6 %, or − erences may be due to omissions of some 0.24% ff 3972 3971 − This research was funded by a NASA Earth System Sciences (ESS) fel- a glacier’s headwater elevation, glaciertion; area, debris cover, aspect and precipita- Higher rates of retreat for cleanglacier glaciers basis, ( compared tolast debris-covered decades, glaciers as noted ( also inBasnett other et studies al., elsewhere (Racoviteanu 2013); et al., 2008a; General trends of thinningage of over debris-covered the tongues lastglaciers, ( four and rapid decades), growth with of thickening pro-glacier lakes towards for the others. terminus for some to 2000); Greater glacier area changesrange for and small, less debris steep cover; glaciers the with amount a of glacier smaller retreat altitudinal is partly influenced by Larger percent ofmalaya debris (14 % cover of onsupraglacial the lakes glaciers glacierized constituting on about area) 6 the compared % of to southern theGlacier northern debris slopes area covered slopes area; of change (2 %),2006’s, amounts the with with to a Hi- higher rate2000 of to retreat 2006) in compared the to last the decade previous ( period ( – – – – – erenced and checked carefully.temperature We for also investigating showed supraglacial features the andThere potential as is a of proxy ASTER a for glacier day generaltongues, thickness. surface as tendency suggested of by surface thickerevation temperature changes supra-glacier trends, and but debris surface the temperature link forinvestigation. is between The most not surface geospatial yet el- debris-covered conclusive datasets and andthis requires the study additional topographic/climatic can links bespatial developed further in patterns of to glacier understand melt, and the the behavior contribution of of glaciers Himalayan to glaciers, water such resources. as Further work would beelevation needed changes. on In order this toagery study, use we to Corona investigate did glacier stereo not elevationof imagery use changes availability a to due of to DEM investigate a the high-resolution constructedproved DEM time from to from constraints Corona the be and 2000’s. im- an the By lack important contrast, data topographic maps source for computing elevation changes when georef- In this study we showed thatof in the spite of Corona intensive, imagery time-consuming1960’s pre-processing for has steps high an important altitude potential ruggedthe for terrain, Himalaya, glacier declassified as change imagery pointed detection in from in data-sparse the other areas studies of (Narama et al., 2007; Bolch et al., 2008a). glacier inventory for thechanges eastern in Himalaya, the and last tories quantify four for decades. glacier this area We part have andimagery, respectively. constructed of elevation Spatial two the trends updated Himalaya, ofdecades based glacier glacier include: invento- on area 1962 and Corona elevation changes and in 2000 the Landsat/ASTER last glacier surges that mightarea induce estimate is an smaller apparent thanet “glacier the al. growth”. 2000 (2002). Besides, area We estimateddebris-covered the speculate tongues both 1987/89 that from by the these our glacier study di maps. and by Mool 6 Summary and conclusions In this study we combined remote sensing data from various sensors to construct a new another study (Kulkarni, 1992b),1987/88 reported based on a Indian glacierized IRS-1A and areathis Landsat data. would of Compared suggest 431 to km an our Corona areaby inventory, loss a subsequent of glacier 42 % growthWe since in consider the the 1960’s–1970’s 2000s the (2.1 decade % 1987/89 yr (based on estimates our to Landsat analysis). be highly unreliable, given that there are no persistent snow as glacial ice in the 1960’s–1970’s source aerial imagery. In contrast, Acknowledgements. lowship (NNX06AF66H), a National Science Foundation doctoral dissertation improvement 5 5 25 20 10 15 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 10.5194/tc- 10.5194/nhess-8- 10.1029/2011gc003513 el, M.: The state and fate of Himalayan ff 3974 3973 , 2006. , 2011. , 2008b. 10.1029/2006GL025862 Fujita, K., Scheel,glaciers, M., Science, 336, Bajracharya, 310–314, S., 2012. and Sto 5-349-2011 Canada, 1985–2005, Remote Sens. Environ., 114, 127–137, 2010. (Nepal Himalaya) derived from stereo imagery, The Cryosphere, 5, 349–358, doi: changes in the Khumbu HimalayaJ. Glaciol., since 54, 1962 592–600, using 2008a. Corona, Landsat TM and ASTERglacier data, motion and potentially dangerousspaceborne glacial imagery, lakes Nat. in the1329-2008 Hazards Mt. Earth Everest region/Nepal Syst. using Sci., 8, 1329–1340, doi: using remote sensing data, Global Planet. Change, 56, 1–12, 2007. vealed by TRMM precipitation radar, Mon. Weather Rev., 133, 149–165, 2005. Himalaya, India, from 1968 to 2006 based on remote sensing, J. Glaciol., 57, 543–556, 2011. estimates of glacierRemote mass Sens. balances Environ., 108, in 327–338, 2007. the Himachal Pradeshmalayas, Prog. (Western Phys. Himalaya, Geog., 33, India), 672–702, 2009a. Himalayas, India during543–556, the 2010. last 40 years based on remote sensing data, J. Glaciol., 54, malaya and Tibet: an assessment2005. and evaluation of results, Quatern. Int., 138–139, 55–58, implications for the monitoring ofdoi: glacier volume changes, Geophys. Res. Lett., 33, L08502, Glaciers and Glacial Lakes, ICIMOD, Kathmandu, 2007. recession of glaciers in Sikkim Himalaya, India, J. Glaciol.,westerlies 59, in 1035–1046, Himalayan 2013. glaciation: review155, and speculative 353–363, discussion, 1998. J. Geol. Soc. London, the Himalayan front, Geochem. Geophy. Geosy., 12, Q07023, doi: Region, International Centre forNepal, Integrated 127 pp., Mountain 2011. Development (ICIMOD), Kathmandu, type glacier in the Nepal Himalaya, Geogr. Ann. A, 66, 249–255, 1984. 2011. Basin (Sikkim Himalaya), SAC/RESA/MWRGGLI/SN/16, Ahmedabad, India, 2001. Andermann, C., Bonnet, S., and Gloaguen, R.: Evaluation of precipitation data sets along Ageta, Y. and Higuchi, K.: Estimation of mass balance components of a summer-accumulation to Jonathan Taylor at Universityimagery of through California-Fullerton the for NASA facilitating Appropriations access Grant to # NNA07CN68G. high-resolution References ship from CU-Boulder.tional A. d’Etudes Racoviteanu’s Spatiales post-doctoral (CNES),NSF-funded research France. Niwot Participation was of Ridge fundedCooperative M. Long-Term by Williams Agreement Ecological was Centre AID-OAA-A-11–00045. Research supportedNASA-funded Na- ASTER (LTER) by Global program the imagery Land and Ice was the Measurements obtained USAID from through Space the (GLIMS) project. We are grateful grant (NSF DDRI award BC 0728075), a CIRES research fellowship, and a graduate fellow- Bolch, T., Kulkarni, A., Kääb, A., Huggel, C., Paul, F., Cogley, J. G., Frey, H., Kargel, J. S., Bolch, T., Pieczonka, T., and Benn, D. I.: Multi-decadal mass loss of glaciers in the Everest area Bolch, T., Menounos, B., and Wheate, R.: Landsat-based inventory of glaciers in western Bolch, T., Buchroithner, M. F., Peters, J., Baessler, M., and Bajracharya, S.: Identification of Bolch, T., Buchroithner, M. F., Pieczonka, T., and Kunert, A.: Planimetric and volumetric glacier Bolch, T.: Climate change and glacier retreat in northern Tien Shan (Kazakhstan/Kyrgyzstan) Bhatt, B. C. and Nakamura, K.: Charactieristics of Monsoon rainfall around the Himalayas re- Bhambri, R., Bolch, T., Chaujar, R. K., and Kulshreshtha, S. C.: Glacier changes in the Garhwal Bhambri, R., Bolch, T., Chaujar, R. K., and Kulshreshth, S. C.: Glacier changes in the Garhwal Bhambri, R. and Bolch, T.: Glacier mapping: a review with special reference to the Indian Hi- Berthier, E., Arnaud, Y., Kumar, R., Ahmad, S., Wagnon, P., and Chevallier, P.: Remote sensing Benn, D. and Owen, L. A.: Equilibrium-line altitudes of the Last Glacial Maximum for the Hi- Berthier, E., Arnaud, Y., Vincent, C., and Remy, F.: Biases of SRTM in high-mountain areas: Benn, D. I. and Owen, L. A.: The role of the Indian summer monsoon and the mid-latitude Basnett, S., Kulkarni, A., and Bolch, T.: The influence of debris cover and glacial lakes on the Bajracharya, S. R. and Shrestha, B. (Eds.): The Status of Glaciers in the Hindu-Kush Himalauan Bajracharya, S. R., Mool, P. K., and Shresta, A.: Impact of Climate Change on Himalayan Bahuguna, I. M., Kulkarni, A. V., Arrawatia, M. L., and Shresta, D. 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K., 5 5 30 25 30 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (last ac- ect on the ff contrast contrast Some clouds on the south end of the im- age; good contrast; no GLIMS gains Minimal snow cover, good contrast clouds in the area of interest s on debris-covered ff s on the Lirung Glacier, Nepal Hi- ff 0.50 m No clouds; good 2.4 m No clouds, excellent 30 m SWIR 90 m TIR 28.5 m VIS and SWIR 90 m TIR 3979 3980 02 Dec 2010 01 Dec 2009 1 Jan 2006 6 Jan 2006 27 Nov 2000 15 m VIS 25 Oct 1962 7.5 m26 Dec 2000 15 m PAN Good contrast, no er, H. H.: ASTER measurement of supraglacial lakes in (last acces: 1 March 2014), 1996. ff ected by debris cover, Nat. 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Glacier Res., 16, 57–66, 1998. vited paper, Symp. Snow, Ice and53, Glacier, 11–15, 9–11 1999. March 1999, Geol. Surv. India Special Publ., Group, Boca Raton, FL, 2003. in the Global Land104–125, Ice 2007. Measurements from Space (GLIMS) Project, Comput. Geosci., 33, WorldView-2 102001000FBA1D00 QuickBird 1010010004BD8700 ASTER AST_05_003112720 SensorCorona KH4 DS009048070DA244 Scene IDLandsat ETM Date Spatial resolution Notes Survey_of_India: National Map Policy, Survey of India, Retrieved 24 October 2010, available Table 1. Srikantia, S. V.: Restriction on maps: a denial of valid geographic information, Curr. Sci. India, Sangewar, C. V. and Shukla, S. P. (Eds.): Inventory of Himalayan Glaciers:Scherler, A D., Contribution Bookhagen, to B., and Strecker, M. R.: Spatially variable response of Himalayan Sakai, A., Nakawo, M., and Fujita, K.: Melt rate of ice cli Sakai, A.: Distribution characteristics and energy balance of ice cli Rees, W. G.: Remote Sensing of Snow and Ice, Taylor & Francis, CRC Press, Taylor and Francis Shanker, R.: Glaciological studies in India, a contribution from Geological Survey of India, In- Zhang, Y., Fujita, K., Liu, S., Liu, Q., and Nuimura, T.: Distribution of debris thickness and its Yanai, M., Li, C., and Song, Z.: Seasonal heating of the Tibetan plateau and its e Wessels, R. L., Kargel, J. S., and Kie USGS-Eros: USGS Declassified Imagery-1, Retrieved 15 August 2011, available at: 5 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | E side (Bhutan) E side (Sikkim) W side (Nepal/China) 3982 3981 N side (China) ) 146 805 977 383 1 − Details ing from Sikkim to China,Nepal as well as parts of W Bhutan and E Number of glaciers Precipitation patterns averaged for the period 1998–2010 in the four cli- Spatial domains used for analysis and their characteristics. 12 487 50 The entire area of the Eastern Himalaya, in this study extend- Parts of Sikkim (Tista basin) and Nepal (Tamor basin) Spatial domain Mean basin elevation (m)Mean rainfall TRMM (mm yr 4931 4819 4658 4491 Table 3. matic/topographic zones in spatial domain 1, derived from TRMM 2B31 data. Table 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 18 ) 1 0.4 ± − ± 6 300 1 6 0.9 ± ± ± 0.43 Area change since 2000 (% yr − 34 106 5 14 ± ± ) 1 − 29 569 4 78 ± ± 0.160.08 – ± ± 0.20 0.24 88 488 10 64 since 1962 (% yr − − ± ± 3984 3983 ) Area change 2 1834 8 – – ± ± ± ) 161 ) 3 3 3 4 3 2 2 ) 1463 2 Topographic parameters for glaciers in spatial domain 1 and sub-regions based on Glacier area changes for the 50 glaciers in spatial domain 2, from 1962 to 2006. 2006 Quickbird 537 Data source1962 Corona2000 Landsat/ASTER Area 551 (km 599 2000 Landsat/ASTER analysis. All parameters are presented on (a) region-by-region and (b) Debris cover (% glacier area) 11 13 14 13 2 (a) Region-wide averages Number of glaciersGlacierized area (km Number of debris-covered tonguesDebris cover area (km (b) Glacier averages 68Minimum elevation (m)Median elevation (m)Maximum elevation (m)Slope 487 (degree) 30Aspect (degree)Mean glacier size (km 162 27 4908 186 7 5702 6793 4760 30 5715 6928 4 4702 109 23 177 5569 6908 4926 5652 6685 5425 236 24 5950 6530 131 23 134 27 180 21 Parameter All NepalLength (km)Thickness (m) SikkimDebris cover fraction (%) Bhutan China 23 24 2 21 23 2 23 23 32 2 31 17 3 27 2 Table 5. ∼ glacier-by-glacier basis from thearea SRTM of DEM. the Debris debris cover covered fraction tongues only. is calculated as % glacier Table 4. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ∗ ∗ ∗ ∗ ∗ 09 14 14 10 − − − − 12 − ∗ ∗ 10 10 10 10 10 × × × × × value P 0.63 5.58 0.58 3.13 0.47 0.0001 0.41 4.57 0.39 1.19 0.25 6.6 0.06 0.63 − − − − − − − 3986 3985 RegressionMaximum elevation Pearson’s r Altitudinal range Median elevation Glacier area Precipitation Minimum elevationPercent debris 0.26 0.33 LongitudeAspect 0.06 0.68 0.04 0.0004 Solar radiationSlopeLatitude 0.17 0.72 0.14 0.26 Correlation is significant at the 0.01 level (2-tailed). ∗ ) 2 23 2 Area change (%)SlopeMinimum elevation (m)Median elevation (m)Altitudinal range (m)Length (km) 5240 31 5625 777 24 4704 2 14 5645 2339 25 8 ParameterArea (km Clean glaciers Debris-covered glaciers Correlations between area change and topographic and climatic variables, arranged Comparison of glacier parameters for clean glaciers vs. debris-covered glaciers. Table 7. in order of strength of correlation. Table 6. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − 0.17 % ±

44 0.92 1.41 0.30 + − − 6.4 % 0.36 ± 7.3 % 35 % 11.4 % % area change Rate of loss yr + − − ) Area change since 1960s 2 20 – – 34 13.5 ± ± 449 706 n/a285 426 577 185 569 3988 3987 Indian 1 : 63topographic 000 maps images IRS-1C, topographic maps ASTER 1960 ∼ –1970s 1987/89 IRS-1C satellite 2000 Landsat TM,

Location map of the study area. The images used in this study: 2000 Landsat, six Glacier area change in Sikkim based on previous studies. The percent area change is StudyThis study Year 1962 Data source Corona KH4 # glcrs 178 Area (km 658 Geological Survey of India (1999) Kulkarni and Narain (1990) ICIMOD Mool et al. (2002) This study 2000 Landsat TM, 2000–2006 ASTER scenes, 2006(Landsat QB 432, and ASTER 321, 2009two QB WV2, spatial 432) are domains: and shownyellow Spatial greyscale polygon), as domain a (WV2), false subset 1 respectively. color of Also (solid spatial composites shown domain turquoise 1 are rectangle); encompassing the Sikkim/Nepal Spatial glaciers. domain 2 (dotted Figure 1. Table 8. given with respect to the 1962 Corona glacier inventory from this study.

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45

3990 3989

2 Precipitation regime over domain 1 expressed as rain rate, from the TRMM 2B31 Spatial patterns in TRMM annual precipitation rate derived from the 3B43 dataset for

Fig. 3

Fig. 2 Figure 3. spatial domain 1. Alsowatershed shown functions. are 2000 the glacierprecipitation four outlines at main are high basins shown altitudes delineatederrors in over in based black. the TRMM on We data. Kanchenjunga topography note summits and several and cells parts of of high Tibet, most likely Figure 2. data averaged for theSeptember, period with 1998–2010. The a graph peakduring shows precipitation the the winter/early in monsoon spring July, period (January–March). and from the June influence to of the northeastern monsoon

48

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47

thickness. Glaciers (d) length and (c) 30 m thickness are prevalent, with an aver- slope; < (b) 3992 3991 area; (a) ) corresponding to topographic/climatic barriers. ◦ 2 km in length and <

) and NE (60 in area, ◦ 2

Fig. 5 . ◦

Frequency distribution of glacier parameters for the 487 glaciers in spatial domain 1 Aspect frequency distribution of the 487 glaciers in spatial domain 1 based on Land-

Fig. 4 Figure 4. based on Landsat/ASTER analysis: Figure 5. sat/ASTER analysis. On average, glaciersdirections: in NW this (300 area are preferrentially oriented towards two smaller than 10 km age slope of 23 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

49

50 glacier altitudinal range (maximum– (a) 3994 3993 glacier area. Debris-covered glaciers are shown as grey solid cir-

(b)

Fig. 7 Dependency of area change 1962–2000 on Spatial patterns in glacier area change derived from 1962 Corona and 2006 QB/WV2 Figure 6. data, shown on ain glacier-by-glacier the basis. southern The and largest northerndata. area parts loss of is the observed image, most for likely a due few to glaciers uncertainties in the baseline Figure 7. minimum elevation) and cles; clean glaciers are shown assmall black glaciers, solid with triangles. Glacier a area lower changes altitudinal are range. larger for clean

Fig.6 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 52

51 2006 QB/WV2 glacier outlines (in (b) 3996 3995

Fig. 8 Close-up view of glacier area changes around the N. and S. Lonak glaciers 1962 to Area changes for some glaciers in the Zema Chhu basin Sikkim from 1962 to 2006: 1962 Corona-based glacier outlines (in blue) and Figure 9. 2000 and 2006, showingarea the for rapid Jongsang growth glacier ofthe in the image the are pro-glacial lower likely lake. right rock There glaciers, corner is showing or no little the accelerated change image. growth in Glaciers of pro-glacial the in lakes. the upper part of (a) Figure 8. orange). In this area, somepro-glacial of lakes. the debris-covered glacier tongues are retreating, creating large

Fig. 9 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

54 53 erences ff 3998 3997 Elevation changes 1960’s–2000 and day temperature trends along a longitudinal Glacier elevation changes for the selected debris-covered tongues from 1960s to

Fig.10 Figure 11. (thinning), with less variability. transect on Zemu glacieratures in are Sikkim, extracted shown from upwardsfrom ASTER starting data about at from 12 the km 29 terminus.zone), from October Surface indicating the 2002. temper- a Temperatures glacier start thinner terminus decreasing debris to cover. the In limit this with area clean we also ice note (middle larger of elevation the di ablation Figure 10. 2000, based on the topographicupper map part and of SRTM the DEM. debris-coveredglacier We area termini note (red and higher areas), for with rates some a glaciers of in general thinning the tendency in low-middle of the part thickening at of the the debris (blue areas).

Fig. 11