Changes of High Altitude Glaciers in the Trans-Himalaya of Ladakh over the Past Five Decades ( 1969 – 2016 )

Climatic differences between monsoonal and cold-arid parts of the South Asian mountain arc account for the uncertainty regarding regional variations in glacier retreat. In this context, the upper Indus Basin of Ladakh, sandwiched between the Himalayan and Karakoram ranges, is of particular interest. The aims of the present study are threefold: to map the glaciers of central and eastern Ladakh, to describe their regional distribution and characteristics in relation to size and topography, and to analyze glacier changes in the selected ranges over the past five decades. The study is based on multi-temporal remote sensing data (Corona and Landsat), supported and validated by several field campaigns carried out between 2007 and 2016. A glacier inventory was carried out for the complete study area, which was subdivided into nine sub-regions for comparison. In general, the glaciers of Ladakh are characterized by their high altitude, as 91% terminate above 5200 m, and by their relatively small size, as 79% of them are smaller than 0.75 km2 and only 4% are larger than 2 km2. The glaciated area of central Ladakh totaled 997 km2 with more than 1800 glaciers in 2002.


Introduction
The 2007 IPCC (Intergovernmental Panel on Climate Change) report predicted that by 2035 the Himalayan region would be ice-free [1].This erroneous forecast initiated a huge interest in regional glacier studies [2][3][4].In contrast to often simplified assumptions of general and mostly rapid glacier retreat, recent studies show a more complex and spatially differentiated pattern of retreat, stability, and advance.Climatic differences between monsoonal and cold-arid regions account for another uncertainty in general trends of glacier change at the Himalayan scale [5][6][7][8][9].Whereas the majority of glaciers in the monsoonal portions of the central and eastern Himalaya, between Himachal Pradesh in the west and Bhutan in the east, are receding at different rates [10], changes are less pronounced in the western Himalaya [11][12][13][14] and in the adjoining Karakoram [15].Some Karakoram glaciers have advanced since the 1990s [16][17][18][19] or have been in balance since the 1970s [20].This suggests that the Trans-Himalayan region of Ladakh is likely to be located at the interface between decreasing and increasing glaciers.
Due to the semi-arid condition of Ladakh, glaciers are relatively small (<0.75 km 2 ) and are typically restricted to high altitudes.Despite their small size, the water stored in these glaciers determines the potential for irrigated crop cultivation, which forms the basis for regional food security and socio-economic development [21][22][23][24].Even small climatic shifts influence water storage and runoff [25,26] and in years with low summer precipitation, snow and ice melt becomes the only water source [5].Thus, the question is not merely whether or not the glaciers retreat, but also how quickly retreat is occurring and what consequences this has for melt water availability [27,28].The perception of the local inhabitants appears to be that glaciers in Ladakh have shrunk drastically over recent decades [29].Despite the importance of melt water runoff, a glacier inventory is still missing and only few studies have documented recent changes in selected regions of Ladakh [14,15,30,31].
The study area is located in the upper Indus Basin [32], sandwiched between the Karakoram and Himalayan Ranges.It includes the Ladakh Range and the Pangong Range to the north of the upper Indus Valley and the ranges of Stok, Rong, Kang Yatze, Korzog, and Zangskar (between Kaltser and Tso Moriri) to the south of the Indus River (Figure 1).It covers an area of about 28,500 km 2 ranging in elevation from about 2800 m in the lowermost sections of the Indus and Shyok Valleys to the highest peaks of about 6700 m a.s.l.(above sea level; all elevations are in m a.s.l.) in the Korzog and Pangong Ranges.
Geosciences 2017, 7, 27 2 of 15 quickly retreat is occurring and what consequences this has for melt water availability [27,28].The perception of the local inhabitants appears to be that glaciers in Ladakh have shrunk drastically over recent decades [29].Despite the importance of melt water runoff, a glacier inventory is still missing and only few studies have documented recent changes in selected regions of Ladakh [14,15,30,31].
The study area is located in the upper Indus Basin [32], sandwiched between the Karakoram and Himalayan Ranges.It includes the Ladakh Range and the Pangong Range to the north of the upper Indus Valley and the ranges of Stok, Rong, Kang Yatze, Korzog, and Zangskar (between Kaltser and Tso Moriri) to the south of the Indus River (Figure 1).It covers an area of about 28,500 km 2 ranging in elevation from about 2800 m in the lowermost sections of the Indus and Shyok Valleys to the highest peaks of about 6700 m a.s.l.(above sea level; all elevations are in m a.s.l.) in the Korzog and Pangong Ranges.The semi-arid climate of Ladakh is caused by the rain shadow effect of the Karakoram and Himalaya.Mean annual precipitation of the upper Indus basin decreases from west to east and south to north [33].In the main administrative center of Leh (3506 m), located in the Indus Valley, mean annual precipitation amounts to approximately 100 mm [34].Roughly one third of the total annual precipitation is associated with westerly disturbances occurring between December and February [31].As in the adjacent Karakoram, slope wind circulation may result in significant underestimation of precipitation [35].The denser cover of grasses and dwarf shrubs at higher altitudes also suggests a vertical gradient in precipitation [36,37].The dominant input of snow into the glacial system occurs in winter, but precipitation may fall as snow at higher altitudes throughout the year.Our own observations, remote sensing data, as well as observations by other research groups [36] confirm regular summer snowfall at altitudes above 5000 m, resulting in increased surface albedo and reduced ablation of snow and ice.Mean monthly temperatures in Leh range from −7.2 °C in January to 17.9 °C in July.Mean annual temperature was 5.6 °C during the period from 1951-1980 [34], which is unusually high for these elevations [38].Due to low mean annual air temperatures and low annual The semi-arid climate of Ladakh is caused by the rain shadow effect of the Karakoram and Himalaya.Mean annual precipitation of the upper Indus basin decreases from west to east and south to north [33].In the main administrative center of Leh (3506 m), located in the Indus Valley, mean annual precipitation amounts to approximately 100 mm [34].Roughly one third of the total annual precipitation is associated with westerly disturbances occurring between December and February [31].As in the adjacent Karakoram, slope wind circulation may result in significant underestimation of precipitation [35].The denser cover of grasses and dwarf shrubs at higher altitudes also suggests a vertical gradient in precipitation [36,37].The dominant input of snow into the glacial system occurs in winter, but precipitation may fall as snow at higher altitudes throughout the year.Our own observations, remote sensing data, as well as observations by other research groups [36] confirm regular summer snowfall at altitudes above 5000 m, resulting in increased surface albedo and reduced ablation of snow and ice.Mean monthly temperatures in Leh range from −7.2 • C in January to 17.9 • C in July.Mean annual temperature was 5.6 • C during the period from 1951-1980 [34], which is unusually high for these elevations [38].Due to low mean annual air temperatures and low annual precipitation, the glaciers in Ladakh are of a continental type [39].The existence of lakes on and beside these glaciers, causing several glacier lake outburst floods [40,41], indicate their polythermal character.
The aim of the present study is to inventory the glaciers of central and eastern Ladakh and to describe their regional distribution and characteristics in relation to size and topography by using Landsat imagery of the new millennium.A historical analysis of the detected glacier changes is then performed based on a select number of mountain ranges over five decades using multi-temporal remote sensing data (Corona and Landsat), further validated by several field campaigns carried out between 2007 and 2016.

Materials and Methods
A remote sensing approach based on Landsat imagery was applied to map the spatial distribution of glaciers.Landsat images from 2002 were used to delineate glacier boundaries using a standardized semi-automatic approach based on the red/shortwave Infrared band ratio [42].Although this method is robust and time-efficient in delineating clean ice, additional manual correction of glacier boundaries is almost always necessary, especially for shadowed areas, debris-covered ice, lakes, and other misclassified pixels [43].The required threshold for image segmentation varied from one region to the other and had to be estimated separately for each individual area of interest [44].The classified ice and snow covered areas were separated into entities on the basis of generated watersheds, extracted from the Global Advanced Spaceborne Thermal Emission and Reflection Radiometer Digital Elevation Model (GDEM) by using the Hydrology Tool in ArcGIS 10.3.1, which were then manually corrected.For further analysis, the separated ice and snow covered areas, labeled by the corresponding watershed number, were transformed to vector data.Polygons larger than 0.02 km 2 were categorized as glaciers and perennial snow cover, conducted by visual image interpretation.
Topographic parameters (elevation, aspect, minimum elevation, and median) were derived by using the GDEM.In order to evaluate the influence of topography on glacier distribution, the hypsographic curve for nine mountain ranges (Figure 1), defined as subregions, as well as the complete study area was plotted against its elevational distribution [45].In order to consider the different range sizes, the percentage of glaciated area was calculated for each mountain range.The topographic parameters of the glaciers (median, aspect, minimum elevation) were compared region wise.
In order to detect glacier changes, multi-temporal and multi-scale remote sensing data were analyzed.Landsat data allow for glacier monitoring from the 1980s and declassified CORONA images from the early US-military reconnaissance survey extend the period to the 1960s [46].The temporal resolution of satellite images for glacier analyses is generally limited by the availability of archived datasets [47].To minimize the effect of seasonal snow cover, images from the period between the end of the ablation season and the first snow fall event were considered optimal for the purpose of the study [48].Although the Trans-Himalaya falls within the rain shadow of the monsoonal air masses, most summer images of the study area are cloud-or snow-covered.Thus, the number of suitable images for the current study decreased significantly (Table 1).
All Landsat images were available in Level 1T showing a shift of less than one Landsat pixel (projected in Universal Transverse Mercator, World Geodetic System (UTM, WGS 84).In order to orthorectify the Corona images, the required Ground Control Points were selected on the Landsat 2002 images (Landsat 2003 for the Lungser Range) and corresponding height-values were derived from the GDEM.The complete process of orthorectification was conducted using the software package ENVI 5.3 (for further details see [31]).
The glaciers were mapped semi-automatically on Landsat images for the selected years.On panchromatic CORONA images, glaciers were digitized on screen in a Geographical Information System (ArcGIS 10.3.1) based on a detailed visual image interpretation, partly confirmed by photographical field records and ground truth data, including Global Positioning System (GPS) measurements.Only categorized glaciers in selected mountain ranges and tributaries were considered for change detection analyses between 1969 and 2016 (Table 1).In order to analyze patterns of front variations, the lengths of selected valley and cirque glaciers were measured.For maximum glacier length, central flowlines were derived from the GDEM using the Hydrology Tool and corrected manually [49].Finally, terminus variations were calculated as the difference between glacier lengths over time periods.This approach allowed for an elimination of subpixel-shifts between the co-registered images.

Results
The hypsographic curve of the study area shows that 68% of the land surface is located between 4400 and 5600 m, with a relative maximum of 13% in the altitudinal class of 4600-4800 m and 4800-5000 m.The relative maximum of the altitudinal zone varies between the mountain ranges from 4400-4600 m in the Stok Range to 5400-5600 m in the Eastern Ladakh Range (Figure 2).
Separate analyses of the mountain ranges illustrate variations along the hypsographic curve, with increasing elevations towards the east.In the Eastern Zangskar, Korzog, and Pangong Ranges, elevation classes below 3800 m do not exist and more than 40% of the mountain ranges are higher than 5200 m; whilst at the other end of the hypsographic distribution, the mountain ranges of Stok and Central Zangskar show only 8% and 18% of area above 5200 m, respectively.

Glacier Distribution
More than 1800 glaciers covered an area of 997 km 2 (1052 km 2 including about 850 perennial snow patches) in central Ladakh in 2002.The glaciers are characterized by their relatively small size: Seventy-nine percent of them are smaller than 0.75 km 2 and only 4% are larger than 2 km 2 .Fifty-seven percent of the glaciers larger than 2 km 2 are located in the Korzog and Central Ladakh Ranges (Figure 3), where the largest glacier with an area of about 6.5 km 2 is located.In comparison to the main Himalayan Range, almost all glaciers are free of debris-cover, illustrative of the importance of snowfall as the main input as opposed to the influence of snow redistribution by avalanches.As the majority of glaciers are located in the Central and Eastern Ladakh Range, the largest ice cover occurs here with more than 300 km 2 in the Central Ladakh Range and about 208 km 2 in the Eastern Ladakh Range.In the west, the smallest glacier cover can be found in the ranges of Stok (13 km 2 ) and Rong (8 km 2 ) (Figure 3).Only in the Pangong Range, with its relatively high overall altitude, does the percentage of glaciated area amount to almost 10%.Due to the large area extent below 4900 m, in the Central Ladakh Range it is reduced to only 6%.Referring only to the regions above 4900 m, where most glaciers are found, the highest percentage are detected in the Central Ladakh Range and the Pangong Range with 15% and 16%, respectively, followed by the Kang Yatze Massif with 11%.The lowest percentage of glaciated area, less than 2%, can be detected in the Rong and Eastern Zangskar Ranges (Figure 4).
Overall, the glaciers of Ladakh are characterized by their high altitudinal termini, with 91% of them situated above 5200 m.In comparison, the minimum altitude of the debris-covered Siachen Glacier, located in the upper Shyok Valley of the eastern Karakoram, reaches approximately 3570 m.However, in the Central Zangskar and Central Ladakh Ranges, about 20% and 24%, respectively, of the glacier tongues stretch down to elevations below 5200 m, whereas in the adjacent Stok Range, about 8% reach this elevation.In all other regions, the glaciers end above 5200 m and even in the Korzog and Rong Ranges above about 5390 m.In all mountain ranges the percentage of glaciated area increases with altitude; the Central Ladakh Range and the Pangong Range showing their maximum above 5800 m with 47% and 43%, respectively (Figure 4).

Glacier Distribution
More than 1800 glaciers covered an area of 997 km 2 (1052 km 2 including about 850 perennial snow patches) in central Ladakh in 2002.The glaciers are characterized by their relatively small size: Seventy-nine percent of them are smaller than 0.75 km 2 and only 4% are larger than 2 km 2 .Fifty-seven percent of the glaciers larger than 2 km 2 are located in the Korzog and Central Ladakh Ranges (Figure 3), where the largest glacier with an area of about 6.5 km 2 is located.In comparison to the main Himalayan Range, almost all glaciers are free of debris-cover, illustrative of the importance of snowfall as the main input as opposed to the influence of snow redistribution by avalanches.As the majority of glaciers are located in the Central and Eastern Ladakh Range, the largest ice cover occurs here with more than 300 km 2 in the Central Ladakh Range and about 208 km 2 in the Eastern Ladakh Range.In the west, the smallest glacier cover can be found in the ranges of Stok (13 km 2 ) and Rong (8 km 2 ) (Figure 3).Only in the Pangong Range, with its relatively high overall altitude, does the percentage of glaciated area amount to almost 10%.Due to the large area extent below 4900 m, in the Central Ladakh Range it is reduced to only 6%.Referring only to the regions above 4900 m, where most glaciers are found, the highest percentage are detected in the Central Ladakh Range and the Pangong Range with 15% and 16%, respectively, followed by the Kang Yatze Massif with 11%.The lowest percentage of glaciated area, less than 2%, can be detected in the Rong and Eastern Zangskar Ranges (Figure 4).
Overall, the glaciers of Ladakh are characterized by their high altitudinal termini, with 91% of them situated above 5200 m.In comparison, the minimum altitude of the debris-covered Siachen Glacier, located in the upper Shyok Valley of the eastern Karakoram, reaches approximately 3570 m.However, in the Central Zangskar and Central Ladakh Ranges, about 20% and 24%, respectively, of the glacier tongues stretch down to elevations below 5200 m, whereas in the adjacent Stok Range, about 8% reach this elevation.In all other regions, the glaciers end above 5200 m and even in the Korzog and Rong Ranges above about 5390 m.In all mountain ranges the percentage of glaciated area increases with altitude; the Central Ladakh Range and the Pangong Range showing their maximum above 5800 m with 47% and 43%, respectively (Figure 4).Another important topographic parameter is the median elevation, which is widely used to estimate the long-term mean equilibrium line altitude (ELA) [50].The ELA is located at approximately 5690 m and it increases from west to northeast.The Central Ladakh and Central Zangskar Range have a mean ELA of about 5500 m, whereas in the Pangong and Korzog Range the averaged ELA is located at an altitude of about 5970 and 5950 m, respectively.About 73% of the glaciated area is located on NW-to NE-facing slopes, whereas south-facing slopes only have an ice cover of 10%.However, due to the steepness of slopes in the upper catchments, including the highest elevations, non-glaciated regions exist, which are prominently located on south facing slopes.The tendency of glacier occurrence in northern aspects confirms the   Another important topographic parameter is the median elevation, which is widely used to estimate the long-term mean equilibrium line altitude (ELA) [50].The ELA is located at approximately 5690 m and it increases from west to northeast.The Central Ladakh and Central Zangskar Range have a mean ELA of about 5500 m, whereas in the Pangong and Korzog Range the averaged ELA is located at an altitude of about 5970 and 5950 m, respectively.About 73% of the glaciated area is located on NW-to NE-facing slopes, whereas south-facing slopes only have an ice cover of 10%.However, due to the steepness of slopes in the upper catchments, including the highest elevations, non-glaciated regions exist, which are prominently located on south facing slopes.The tendency of glacier occurrence in northern aspects confirms the Another important topographic parameter is the median elevation, which is widely used to estimate the long-term mean equilibrium line altitude (ELA) [50].The ELA is located at approximately 5690 m and it increases from west to northeast.The Central Ladakh and Central Zangskar Range have a mean ELA of about 5500 m, whereas in the Pangong and Korzog Range the averaged ELA is located at an altitude of about 5970 and 5950 m, respectively.About 73% of the glaciated area is located on NW-to NE-facing slopes, whereas south-facing slopes only have an ice cover of 10%.However, due to the steepness of slopes in the upper catchments, including the highest elevations, non-glaciated regions exist, which are prominently located on south facing slopes.The tendency of glacier occurrence in northern aspects confirms the importance of shadowing effects and radiation incidence in affecting glacier mass balance.Additionally, a slight east-west asymmetry of glaciated areas can be observed, with more ice-covered areas in the east.This can be explained by more effective melting on western slopes in the afternoon when the combination of potential incident solar radiation and air temperature is at a maximum [51,52].This asymmetric distribution is more accentuated if the snow cover distribution is also considered (Figure 5).importance of shadowing effects and radiation incidence in affecting glacier mass balance.Additionally, a slight east-west asymmetry of glaciated areas can be observed, with more ice-covered areas in the east.This can be explained by more effective melting on western slopes in the afternoon when the combination of potential incident solar radiation and air temperature is at a maximum [51,52].This asymmetric distribution is more accentuated if the snow cover distribution is also considered (Figure 5).

Central Ladakh Range
The glacier changes are shown for two watersheds of the Central Ladakh Range.The first example is the catchment of Leh, located in a northern tributary of the Indus in the Central Ladakh Range, with elevations from 3280 to 5750 m.In the upper catchment, two glaciers and some small perennial snow patches exist.The Phutse Glacier in close proximity to the Khardong La (Figure 6) is located at the western side of the catchment on the NE to E-facing slopes above 5365 m.Its area decreased from 0.74 km 2 in 1969 to 0.64 km 2 in 2002 (13%, 0.4% yr −1 ) and lost another 0.04 km 2 by 2016 (6%, 0.4% yr −1 ).In the same observation period, the glacier front retreated by about 248 m (5.3 m yr −1 ).The glacier retreat was accelerated by a proglacial lake which caused two small glacier lake outburst floods in 1998 and 2006 (pers.comm.Tashi Morup and [53,54]).

Central Ladakh Range
The glacier changes are shown for two watersheds of the Central Ladakh Range.The first example is the catchment of Leh, located in a northern tributary of the Indus in the Central Ladakh Range, with elevations from 3280 to 5750 m.In the upper catchment, two glaciers and some small perennial snow patches exist.The Phutse Glacier in close proximity to the Khardong La (Figure 6) is located at the western side of the catchment on the NE to E-facing slopes above 5365 m.Its area decreased from 0.74 km 2 in 1969 to 0.64 km 2 in 2002 (13%, 0.4% yr −1 ) and lost another 0.04 km 2 by 2016 (6%, 0.4% yr −1 ).In the same observation period, the glacier front retreated by about 248 m (5.3 m yr −1 ).The glacier retreat was accelerated by a proglacial lake which caused two small glacier lake outburst floods in 1998 and 2006 (pers.comm.Tashi Morup and [53,54]).
Geosciences 2017, 7, 27 7 of 15 importance of shadowing effects and radiation incidence in affecting glacier mass balance.Additionally, a slight east-west asymmetry of glaciated areas can be observed, with more ice-covered areas in the east.This can be explained by more effective melting on western slopes in the afternoon when the combination of potential incident solar radiation and air temperature is at a maximum [51,52].This asymmetric distribution is more accentuated if the snow cover distribution is also considered (Figure 5).

Central Ladakh Range
The glacier changes are shown for two watersheds of the Central Ladakh Range.The first example is the catchment of Leh, located in a northern tributary of the Indus in the Central Ladakh Range, with elevations from 3280 to 5750 m.In the upper catchment, two glaciers and some small perennial snow patches exist.The Phutse Glacier in close proximity to the Khardong La (Figure 6) is located at the western side of the catchment on the NE to E-facing slopes above 5365 m.Its area decreased from 0.74 km 2 in 1969 to 0.64 km 2 in 2002 (13%, 0.4% yr −1 ) and lost another 0.04 km 2 by 2016 (6%, 0.4% yr −1 ).In the same observation period, the glacier front retreated by about 248 m (5.3 m yr −1 ).The glacier retreat was accelerated by a proglacial lake which caused two small glacier lake outburst floods in 1998 and 2006 (pers.comm.Tashi Morup and [53,54]).Nangtse Glacier is the second glacier in the catchment, located above 5305 m on the N to NW-facing slopes and retreating at a slightly lower rate.Its area decreased from 0.45 km 2 in 1969 to 0.42 km 2 in 2002 (7%, 0.2% yr −1 ) to 0.39 km 2 in 2016 (7%, 0.5% yr −1 ).
The second example, the Hemis Shukpachan catchment, is located approximately 50 km to the west of Leh.The elevation of the north-south oriented valley ranges from 3000 to 5670 m.At an altitude of approximately 4900 m, this valley is subdivided into an eastern and a western branch (Figure 7).In the eastern tributary, one cirque glacier reaches down to 5130 m and one hanging glacier to 5240 m; while in the western tributary, three cirque glaciers are located above 5090 m.In front of all cirque glaciers, large ice filled moraines including tills, terminal moraines, and two proglacial lakes are present.The uppermost lake, located at an elevation of 5310 m, is frozen almost year-round.The glaciated area is largely located on NW-to N-facing slopes, and it is only at its uppermost reaches that it is dominantly exposed to the west.The total glaciated area, including the area covered by perennial snow, decreased from 4.1 to 2.5 km 2 between 1969 and (38%, 0.8% yr −1 ).Three cirque glaciers show a decrease of about 30% (0.7% yr −1 ).The steep north-facing glacier (Figure 7A) shows a drastic decrease of about 53% (1.1% yr −1 ).Contrary to the decrease of the glaciated area, the annual front retreat is comparably low, with a mean rate of about 3.9 m yr −1 .
Nangtse Glacier is the second glacier in the catchment, located above 5305 m on the N to NWfacing slopes and retreating at a slightly lower rate.Its area decreased from 0.45 km 2 in 1969 to 0.42 km 2 in 2002 (7%, 0.2% yr −1 ) to 0.39 km 2 in 2016 (7%, 0.5% yr −1 ).
The second example, the Hemis Shukpachan catchment, is located approximately 50 km to the west of Leh.The elevation of the north-south oriented valley ranges from 3000 to 5670 m.At an altitude of approximately 4900 m, this valley is subdivided into an eastern and a western branch (Figure 7).In the eastern tributary, one cirque glacier reaches down to 5130 m and one hanging glacier to 5240 m; while in the western tributary, three cirque glaciers are located above 5090 m.In front of all cirque glaciers, large ice filled moraines including tills, terminal moraines, and two proglacial lakes are present.The uppermost lake, located at an elevation of 5310 m, is frozen almost year-round.The glaciated area is largely located on NW-to N-facing slopes, and it is only at its uppermost reaches that it is dominantly exposed to the west.The total glaciated area, including the area covered by perennial snow, decreased from 4.1 to 2.5 km 2 between 1969 and 2016 (38%, 0.8% yr −1 ).Three cirque glaciers show a decrease of about 30% (0.7% yr −1 ).The steep north-facing cirque glacier (Figure 7A) shows a drastic decrease of about 53% (1.1% yr −1 ).Contrary to the decrease of the glaciated area, the annual front retreat is comparably low, with a mean rate of about 3.9 m yr −1 .

Stok Range
The Stok Range is located on the southern bank of the Indus River, opposite to Leh.The elevation of the SSW-NNE oriented Stok Valley ranges from 3890 m up to the highest peak of Stok Kangri (6140 m) (Figure 8).The minimum elevation of the six NW-NE-facing glaciers ranges between 5240 and 5420 m.In front of the valley and cirque glaciers, large terminal moraines mark the front position during the Little Ice Age (Figure 9).

Stok Range
The Stok Range is located on the southern bank of the Indus River, opposite to Leh.The elevation of the SSW-NNE oriented Stok Valley ranges from 3890 m up to the highest peak of Stok Kangri (6140 m) (Figure 8).The minimum elevation of the six NW-NE-facing glaciers ranges between 5240 and 5420 m.In front of the valley and cirque glaciers, large terminal moraines mark the front position during the Little Ice Age (Figure 9).The glaciated area decreased from 4.42 km 2 in 1969 to 4.02 km 2 in 2000 (0.3% yr −1 ) and to 3.43 km 2 in 2016 (0.9% yr −1 ).The main reason for the drastic decrease of the glaciated area is the disappearance of snow and ice on the NE-E facing slopes.As a consequence, the small cirque glacier with a snow covered backward slope shows a relative decrease of 49%.The glacier at the E-facing slope of the neighboring Golep Kangri (5900 m, Figure 8) broke into two parts, thus the relative decrease amounts to 22%.Contrary to the decreasing rates of the glaciated area, the glacier tongue retreat is relatively low with an average retreat of about 1.7 m yr −1 between 1969 and 2016.The tongues of three glaciers retreated by more than 100 m (117, 123, and 135 m), whereas two glaciers are characterized by stable tongues, with a retreat of less than 20 m.However, an increase of the glacier retreat to 3.1 m yr −1 can be observed between 2000 and 2016, while the glacier retreat again decreased to 0.1 m yr −1 between 2009 and 2016.These variations might be caused by annual differences in seasonal snow cover and related image interpretations (Figure 10).The glaciated area decreased from 4.42 km 2 in 1969 to 4.02 km 2 in 2000 (0.3% yr −1 ) and to 3.43 km 2 in 2016 (0.9% yr −1 ).The main reason for the drastic decrease of the glaciated area is the disappearance of snow and ice on the NE-E facing slopes.As a consequence, the small cirque glacier with a snow covered backward slope shows a relative decrease of 49%.The glacier at the E-facing slope of the neighboring Golep Kangri (5900 m, Figure 8) broke into two parts, thus the relative decrease amounts to 22%.Contrary to the decreasing rates of the glaciated area, the glacier tongue retreat is relatively low with an average retreat of about 1.7 m yr −1 between 1969 and 2016.The tongues of three glaciers retreated by more than 100 m (117, 123, and 135 m), whereas two glaciers are characterized by stable tongues, with a retreat of less than 20 m.However, an increase of the glacier retreat to 3.1 m yr −1 can be observed between 2000 and 2016, while the glacier retreat again decreased to 0.1 m yr −1 between 2009 and 2016.These variations might be caused by annual differences in seasonal snow cover and related image interpretations (Figure 10).The glaciated area decreased from 4.42 km 2 in 1969 to 4.02 km 2 in 2000 (0.3% yr −1 ) and to 3.43 km 2 in 2016 (0.9% yr −1 ).The main reason for the drastic decrease of the glaciated area is the disappearance of snow and ice on the NE-E facing slopes.As a consequence, the small cirque glacier with a snow covered backward slope shows a relative decrease of 49%.The glacier at the E-facing slope of the neighboring Golep Kangri (5900 m, Figure 8) broke into two parts, thus the relative decrease amounts to 22%.Contrary to the decreasing rates of the glaciated area, the glacier tongue retreat is relatively low with an average retreat of about 1.7 m yr −1 between 1969 and 2016.The tongues of three glaciers retreated by more than 100 m (117, 123, and 135 m), whereas two glaciers are characterized by stable tongues, with a retreat of less than 20 m.However, an increase of the glacier retreat to 3.1 m yr −1 can be observed between 2000 and 2016, while the glacier retreat again decreased to 0.1 m yr −1 between 2009 and 2016.These variations might be caused by annual differences in seasonal snow cover and related image interpretations (Figure 10).

Kang Yatze Range
The Kang Yatze (or Nimaling) Range is located within the upper catchment of the Markha Valley, south of the Upper Indus Valley.It covers an area of about 1000 km 2 .The NW-SE-oriented ridge increases in altitude from south to north from 3800 m up to 6400 m.Small glaciers are most common, though larger valley glaciers with a maximum of 5.2 km 2 are found in the northern part of the massif.As in other regions of Ladakh, the glaciers are located on the N-facing slopes.The glaciated area of the Kang Yatze Massif (Figure 11) from 96.42 km 2 in 1969 to 82.6 km 2 in 2010, resulting in a relative ice cover loss of 14.3% (0.3% yr −1 ) [31] and between 1969 and 2014

Kang Yatze Range
The Kang Yatze (or Nimaling) Range is located within the upper catchment of the Markha Valley, south of the Upper Indus Valley.It covers an area of about 1000 km 2 .The NW-SE-oriented ridge increases in altitude from south to north from 3800 m up to 6400 m.Small glaciers are most common, though larger valley glaciers with a maximum of 5.2 km 2 are found in the northern part of the massif.As in other regions of Ladakh, the glaciers are located on the N-facing slopes.The glaciated area of the Kang Yatze Massif (Figure 11) decreased from 96.42 km 2 in 1969 to 82.6 km 2 in 2010, resulting in a relative ice cover loss of 14.3% (0.3% yr −1 ) [31] and between 1969 and 2014

Kang Yatze Range
The Kang Yatze (or Nimaling) Range is located within the upper catchment of the Markha Valley, south of the Upper Indus Valley.It covers an area of about 1000 km 2 .The NW-SE-oriented ridge increases in altitude from south to north from 3800 m up to 6400 m.Small glaciers are most common, though larger valley glaciers with a maximum of 5.2 km 2 are found in the northern part of the massif.As in other regions of Ladakh, the glaciers are located on the N-facing slopes.The glaciated area of the Kang Yatze Massif (Figure 11) decreased from 96.42 km 2 in 1969 to 82.6 km 2 in 2010, resulting in a relative ice cover loss of 14.3% (0.3% yr −1 ) [31] and between 1969 and 2014 (excluding the cloud covered glacier in the northeast) the ice cover decreased by about 21.4% (0.5% yr −1 ).The decreasing rate of ice coverage varied over the past four decades: by 0.3% yr −1 from 1969 to 1991, by 0.6% yr −1 from 1991 to 2002, and by 0.2% yr −1 from 2002 to 2010 [31], whereas the decrease amounted to 0.8% yr −1 between 2002 and 2014.The glacier retreat derived for 67 valley and cirque glaciers is 144 m (3.2 m yr −1 ) on average between 1969 and 2014.The maximum retreat was 472 m (10.5 m yr −1 ) caused by a proglacial lake.

Lungser Range
The Lungser Range is part of the Korzog Range which belongs to the Changthang region in eastern Ladakh and represents the southwesternmost extension of the Tibetan Plateau (Figure 12).The N-W oriented range covers an area of about 1000 km 2 and is bordered on its western side by the endorheic lake Tso Moriri, covering an area of about 145 km 2 at an altitude of 4500 m.The elevation ranges from 4100 m at the northwestern side to the highest peaks of Lungser Kangri (6670 m) and Chamser Kangri (6645 m).Caused by the gently sloped topography, a relatively large number of glaciers (21%) are larger than 1 km 2 .The minimum elevation of the glaciers is located at about 5500 m and the mean ELA amounts to 6100 m, which is significantly higher compared to the whole Korzog Range.
The glaciated area of the Lungser Range decreased from 61. (excluding the cloud covered glacier in the northeast) the ice cover decreased by about 21.4% (0.5% yr −1 ).The decreasing rate of ice coverage varied over the past four decades: by 0.3% yr −1 from 1969 to 1991, by 0.6% yr −1 from 1991 to 2002, and by 0.2% yr −1 from 2002 to 2010 [31], whereas the decrease amounted to 0.8% yr −1 between 2002 and 2014.The glacier retreat derived for 67 valley and cirque glaciers is 144 m (3.2 m yr −1 ) on average between 1969 and 2014.The maximum retreat was 472 m (10.5 m yr −1 ) caused by a proglacial lake.

Lungser Range
The Lungser Range is part of the Korzog Range which belongs to the Changthang region in eastern Ladakh and represents the southwesternmost extension of the Tibetan Plateau (Figure 12).The N-W oriented range covers an area of about 1000 km 2 and is bordered on its western side by the endorheic lake Tso Moriri, covering an area of about 145 km 2 at an altitude of 4500 m.The elevation ranges from 4100 m at the northwestern side to the highest peaks of Lungser Kangri (6670 m) and Chamser Kangri (6645 m).Caused by the gently sloped topography, a relatively large number of glaciers (21%) are larger than 1 km 2 .The minimum elevation of the glaciers is located at about 5500 m and the mean ELA amounts to 6100 m, which is significantly higher compared to the whole Korzog Range.
The glaciated area of the Lungser Range decreased from 61.

Discussion
The study presents a regional glacier inventory for the Trans-Himalaya of Ladakh with information on the distribution and recent changes of glaciers.Due to the limited availability of cloud-free remote sensing data and in order to minimize the influence of seasonal snow cover on

Discussion
The study presents a regional glacier inventory for the Trans-Himalaya of Ladakh with information on the distribution and recent changes of glaciers.Due to the limited availability of cloud-free remote sensing data and in order to minimize the influence of seasonal snow cover on glacier change detection, the selection of satellite imagery had to include data from different years for different mountain ranges.
The glaciers are generally characterized by their high altitudes located above 5200 m.As opposed to the glaciers of the Greater Himalayan Range and the Karakoram [16], most glaciers of Ladakh are free from debris cover, illustrating the primary importance of snowfall on glacier feeding in contrast to snow redistribution by avalanches.The clear tendency to northern aspects confirms the importance of shadowing effects and radiation incidence in affecting glacier mass balances.Additionally, the detectable asymmetry of the east-west-distribution can be explained by more effective glacier melting on western slopes in the afternoon when the cumulative effect of potential incident solar radiation and air temperature is at a maximum [51,55].
The initial hypohesis that Ladakh is located at the interface between decreasing and increasing glaciers can not be generalized, as the differences in glacier dynamics within the Trans-Himalayan study area do not allow for a simple interpretation.Due to the high variability of glacier change with a generally decreasing trend and a few stable glaciers, it becomes obvious that extrapolations even on a regional scale are problematic.Whereas the change detection analyses of Kang Yatse and Lungser Ranges show increasing losses in the glaciated area for the most recent observation period, the examples of the Central Ladakh Range show considerably lower decreasing rates.However, the observed decreasing rate between 1969 and 2002 is higher than in the Ravi Basin [12].The results are in contrast to the observed decline of glacier retreat between 2002 and 2010/13 in the Ravi Basin and the glacier increase in the upper Shyok Basin between 2002 and 2010 [15].These comparisons between adjoining regions clearly show that glacier dynamics in Ladakh are in the interface between stable conditions and drastic decrease.The more differentiated picture of Himalayan glacier response to climate change can be interpreted as a result of the huge interest in cryospheric changes in the aftermath of the 2007 IPCC report and controversy.

Conclusions
Although glacier decrease in Ladakh is not as pronounced as in many other Himalayan regions, the consequences of small changes are almost always crucial for the functioning of irrigated agriculture.As local village communities are entirely dependent on the meltwater supply, such glacier dynamics directly affect their livelihoods and the sustainability of land use systems.These socio-glaciological interactions need further investigation.

Figure 1 .
Figure 1.The study area: mountain ranges of central and eastern Ladakh, Northwest India.

Figure 1 .
Figure 1.The study area: mountain ranges of central and eastern Ladakh, Northwest India.

Figure 2 .
Figure 2. Hypsographic curve of the study area, differentiated for individual mountain ranges (altitude derived from the Global Digital Elevation Model (GDEM).

Figure 2 .
Figure 2. Hypsographic curve of the study area, differentiated for individual mountain ranges (altitude derived from the Global Digital Elevation Model (GDEM).

Figure 4 .
Figure 4. Percentage of glaciated area in relation to altitudinal zones (altitude derived from GDEM).

Figure 4 .
Figure 4. Percentage of glaciated area in relation to altitudinal zones (altitude derived from GDEM).

Figure 4 .
Figure 4. Percentage of glaciated area in relation to altitudinal zones (altitude derived from GDEM).

Figure 5 .
Figure 5. Aspect of the glaciated area and perennial snow cover patches in the subregions of Ladakh.

Figure 5 .
Figure 5. Aspect of the glaciated area and perennial snow cover patches in the subregions of Ladakh.

Figure 5 .
Figure 5. Aspect of the glaciated area and perennial snow cover patches in the subregions of Ladakh.

Figure 7 .
Figure 7. N-facing glacier with a proglacial lake (A); glacier tongue in the eastern part of the catchment in 2007 (B) and 2014 (C); Glaciers (in blue color) in the upper catchment of Hemis Shukpachan (D).

Figure 7 .
Figure 7. N-facing glacier with a proglacial lake (A); glacier tongue in the eastern part of the catchment in 2007 (B) and 2014 (C); Glaciers (in blue color) in the upper catchment of Hemis Shukpachan (D).

Figure 8 .
Figure 8. Upper catchment of the Stok Glacier seen from the summit of Stok Kangri (6140 m) with the Golep Kangri (5900 m) in the background in 2007 and 2014 (the yellow point in Figure 10 marks the camera position).

Figure 9 .
Figure 9. Terminal moraines of the Golep Glacier (left) and an unnamed glacier (right) of the Stok Range in 2008 (the orange point in Figure 10 marks the camera position).

Figure 8 .
Figure 8. Upper catchment of the Stok Glacier seen from the summit of Stok Kangri (6140 m) with the Golep Kangri (5900 m) in the background in 2007 and 2014 (the yellow point in Figure 10 marks the camera position).

Geosciences 2017, 7 , 27 9 of 15 Figure 8 .
Figure 8. Upper catchment of the Stok Glacier seen from the summit of Stok Kangri (6140 m) with the Golep Kangri (5900 m) in the background in 2007 and 2014 (the yellow point in Figure 10 marks the camera position).

Figure 9 .
Figure 9. Terminal moraines of the Golep Glacier (left) and an unnamed glacier (right) of the Stok Range in 2008 (the orange point in Figure 10 marks the camera position).

Figure 9 .
Figure 9. Terminal moraines of the Golep Glacier (left) and an unnamed glacier (right) of the Stok Range in 2008 (the orange point in Figure 10 marks the camera position).

Figure 10 .
Figure 10.Satellite images from 1969, 2000, 2009, and 2016 showing the glaciers (in blue color in the Landsat images) in the upper catchment of the Stok Valley (the yellow and orange points indicate the camera positions in Figures 8 and 9).

Figure 10 .
Figure 10.Satellite images from 1969, 2000, 2009, and 2016 showing the glaciers (in blue color in the Landsat images) in the upper catchment of the Stok Valley (the yellow and orange points indicate the camera positions in Figures 8 and 9).
Figure 10.Satellite images from 1969, 2000, 2009, and 2016 showing the glaciers (in blue color in the Landsat images) in the upper catchment of the Stok Valley (the yellow and orange points indicate the camera positions in Figures 8 and 9).

Geosciences 2017, 7 , 27 10 of 15 Figure 10 .
Figure 10.Satellite images from 1969, 2000, 2009, and 2016 showing the glaciers (in blue color in the Landsat images) in the upper catchment of the Stok Valley (the yellow and orange points indicate the camera positions in Figures 8 and 9).
21 km 2 in 1969 to 55.44 km 2 in 2003 and to 50.37 km 2 in 2014, resulting in a relative ice cover loss of 17.7% (0.4% yr −1 ).As in the Kang Yatze Massif, the mean annual rate of decrease rose to 0.8% yr −1 between 2003 and 2014.Glacier length measurements of 39 valley and cirque glaciers indicated an averaged retreat of about 2.6 m•yr −1 between 1969 and 2014, whereas the retreat rates were almost doubled between 2003 and 2014 to 4.2 m•yr −1 .In total, 19 glaciers are characterized by a retreat of more than 100 m; with a maximum of 330 m.No proglacial lakes with direct contact to those glaciers with the highest length reduction can be detected.Geosciences 2017, 7, 27 11 of 15 21 km 2 in 1969 to 55.44 km 2 in 2003 and to 50.37 km 2 in 2014, resulting in a relative ice cover loss of 17.7% (0.4% yr −1 ).As in the Kang Yatze Massif, the mean annual rate of decrease rose to 0.8% yr −1 between 2003 and 2014.Glacier length measurements of 39 valley and cirque glaciers indicated an averaged retreat of about 2.6 m•yr −1 between 1969 and 2014, whereas the retreat rates were almost doubled between 2003 and 2014 to 4.2 m•yr −1 .In total, 19 glaciers are characterized by a retreat of more than 100 m; with a maximum of 330 m.No proglacial lakes with direct contact to those glaciers with the highest length reduction can be detected.

Figure 12 .
Figure 12.Glaciers of the Lungser Range to the east of the Tso Moriri lake.

Figure 12 .
Figure 12.Glaciers of the Lungser Range to the east of the Tso Moriri lake.

Table 1 .
Satellite data and Digital Elevation Model (DEM) used in this study (Pan = panchromatic, VIS = visible, IR = Infrared).