Early 21st century spatially detailed elevation changes of Jammu and Kashmir glaciers (Karakoram–Himalaya)
Introduction
Glaciers in the Karakoram–Himalaya are influenced in different intensity by the Indian summer monsoon, the mid-latitude winter westerlies and the south-east Asian monsoon (Bolch et al., 2012, Wiltshire, 2014). Previous geodetic glacier mass balance studies have reported heterogeneous glacier surface elevation (and mass) changes in high-mountain Asia (HMA) including Karakoram–Himalaya (Kääb et al., 2012, Gardelle et al., 2013, Kääb et al., 2015, Brun et al., 2017, Lin et al., 2017). Such observations are quite important for observing the impact of climate perturbations and changes on glaciers in the region (Kääb et al., 2012, Gardelle et al., 2013), and as a reference for modeling of current changes and to provide future projections (Wiltshire, 2014, Kraaijenbrink et al., 2017).
Karakoram is particularly known for the occurrences of glacier surges – a rapid advance of the glacier front within a few weeks to several years (Copland et al., 2011, Bhambri et al., 2013, Rankl et al., 2014, Bhambri et al., 2017). Surge-type glaciers show unique patterns of elevation changes in their different phases (quiescent and surge) (Gardelle et al., 2012, Rankl and Braun, 2016). The glaciers thin significantly along their lower reaches while thickening occurs upstream during the quiescent phase. The glaciers relocate the ice mass from upstream to their lower reaches during the surge, resulting in thickening in the lower areas and thinning in the upper catchments (Rankl and Braun, 2016). The relocation of ice mass may change the glacier's climate sensitivity and downwasting potential.
In the recent years several promising remote-sensing tools have been deployed to determine glacier elevation and mass changes in the Karakoram–Himalaya (Bolch et al., 2011, Kääb et al., 2012, Gardelle et al., 2013, Vijay and Braun, 2016, Ragettli et al., 2016, Bolch et al., 2017, Brun et al., 2017). With the declassification of the United States' spy satellite stereo images (Corona KH-4 and Hexagon KH-9) observations dating back to the 1960s became available and quantitative photogrammetric analysis started (Holzer et al., 2015, Ragettli et al., 2016, Bolch et al., 2017). Since the beginning of the 21st century, significant advances were made due to the increasing availability of different sensors and satellite platforms (eg. the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) since 1999, the Shuttle Radar Topography Mission (SRTM) in February 2000, the Système pour l’Observation de la Terre 5 (SPOT5) since 2002, the Ice, Cloud, and land Elevation Satellite (ICESat) during 2003–2009 and the TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) since 2010). For the Karakoram–Himalaya alone, several studies have reported glacier elevation and mass changes in the early 21st century (Fig. 1 and Supplementary Table 2). Few studies have also estimated glacier area/length changes, in particular, in the Jammu and Kashmir (Kamp et al., 2011, Bhambri et al., 2013, Bhambri et al., 2017). However, little is known about glacier elevation/mass changes in the transition of the Karakoram to the Himalaya region. This region is interesting since the MLW is the major contributor of precipitation and the influence of the ISM is limited (Bolch et al., 2012). The Indian state, Jammu and Kashmir comprises two distinct glacierized regions; Jammu and Kashmir West, belonging to the Himalaya (abbreviated as JK West hereafter) and Jammu and Kashmir East located in the Karakoram (abbreviated as JK East hereafter). Kääb et al. (2012) showed the first large-scale glacier elevation change estimates for both the regions using repeat overpasses of the ICESat laser altimeter (2003–2009) and extrapolating to the SRTM elevations (2000). Due to the spacing of the ICESat overpasses their observations left a large fraction of the glacierized region, including many small glaciers, unobserved. In a recent work, Brun et al. (2017) included these regions in their region-wide geodetic glacier mass balance estimates for the period 2000–2016. They applied a linear regression over a time-series of ASTER digital elevation models (DEMs) spanning over the period 2000–2016. So far much attention has been paid to the regional analysis leaving a scope for individual glacier analysis in these regions. Few studies were based on the combination of SRTM and TanDEM-X DEMs only. Both data sets were derived by bi-static radar interferometry and demonstrated their potential to measure glacier elevation changes in HMA (Supplementary Table 2). However, this technique has not been applied to the Jammu and Kashmir region before.
Therefore, the objectives of this study are
- 1.
to measure spatially detailed glacier elevation and mass changes for the JK West and the JK East regions in the early 21st century. For this we used the digital elevation models from SRTM (2000) and interferometrically processed TanDEM-X data acquired in 2012.
- 2.
to investigate the influence of glacier surface properties (supraglacial debris, supgraglacial lakes, ponds and ice cliffs) on glacier elevation changes since those properties have been assigned considerable relevance for melt (Anderson and Anderson, 2016, Kraaijenbrink et al., 2017, Sakai et al., 2002).
- 3.
to investigate the status of surge-type glaciers in Jammu and Kashmir during 2000–2012.
Section snippets
Study area
The JK West glaciers (∼1570 km2) are situated in the Zanskar region of southern Ladakh, Himalaya. The region is a high altitude semi-desert (mean elevation ∼ 3000 m) containing several massifs (e.g. Nun Massif (34.0°N, 76.0°E) ∼7135 m a.s.l). The high mountains of this region shield the area from the ISM influences and create a rain shadow zone (Shukla and Qadir, 2016). Therefore, the region receives more than 80% of its annual precipitation from the MLW during November-April, as observed at
Surface elevation and mass changes
We used the SRTM DEM and bistatic TanDEM-X data to estimate surface elevation changes during 2000–2012. The SRTM was conducted in order to acquire X- and C-band interferometric synthetic aperture radar (InSAR) data between 11-Feb-2000 and 22-Feb-2000. The prime objective of the mission was to obtain a near-global DEM (Hoffmann and Walter, 2006). The TanDEM-X satellite was launched on 21-Jun-2010 complementing its twin satellite TerraSAR-X. It is a constellation of two nearly identical X-band
Glacier surface elevation changes in the Karakoram–Himalaya
We observe clear surface lowering for most of the glacierized area in the JK West region during 2000–2012 (Fig. 2). For the entire JK West region (∼ 1570 km2) we found a mean elevation change of −0.50 ± 0.28 m yr−1 in this period (Table 1). On the other hand, the elevation change pattern in the JK East region (2261 km2) is very heterogeneous, especially due to numerous surge-type glaciers (Fig. 3). Overall, it is less negative in JK East with −0.19 ± 0.22 m yr −1 surface lowering. On average,
Surface elevation and mass changes in the Karakoram–Himalaya: a comparison with previous studies
Numerous studies, based on different datasets, have indicated a transition from less negative or positive glacier elevation changes in the Karakoram compared to considerable mass loss in the Himalaya for early 21st century (Fig. 1 and Supplementary Table 2). Fig. 1 shows the mass change rates and scaled elevation change rates (per unit area) observed by previous studies including this one. Our reported values are consistent with the published studies and agree with the transitional changes in
Conclusions
This study presents spatially detailed glacier elevation change observations for the Jammu and Kashmir region (Karakoram–Himalaya) for the period 2000–2012. The combination of the SRTM DEM and the bistatic TanDEM-X data for quantifying such observations in high-mountain Asia has been proven to be a suitable technique by previous studies. The consistency between our estimates and the previous study using time-series of ASTER DEMs strengthens the suitability of SRTM–TanDEM-X combination for such
Acknowledgments
We thank Fanny Brun for sharing elevation change data of Jammu and Kashmir, and Simone Schauwecker for sharing debris-cover thickness data of Bara Shigri Glacier. The study was funded by the HGF Alliance “Remote Sensing and Earth System Dynamics” (HA-310) and the DLR/BMWi project TanDEM-ICE (contract 50EE1414). Saurabh Vijay acknowledges funding from VILLUM FONDEN blokstipendier. The TanDEM-X data was kindly provided under DLR AO XTI_GLAC0264. Landsat data and SRTM/SIR-C data were kindly
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