The Karakoram-Himalaya mountain ranges, spread across Pakistan, India, China, Bhutan, and Nepal, are a home for thousands of glaciers. Glaciers are the natural reservoirs of freshwater which receive mass (snowfall) during cold periods and lose mass by releasing meltwater in summer months.
The snow and glacier ice melt from the Karakoram-Himalaya are a valuable source of water for various infrastructural necessities (ex. drinking water, irrigation, hydropower etc.) for a large Asian population. Therefore, the state and fate of these glaciers are needed to be studied.
Credit: Saurabh Vijay
Glacier area change (or frontal change) and mass (or volume) change are the two principal glaciological variables to assess glacier health. However, the scientific community has made a consensus that glacier mass change is a better estimate to study the state of glacier health and its links with regional and global climate change.
Several scientific groups have been monitoring the glaciers of this region using field-based methods for the last few decades. However, the numbers of investigated glaciers in the region are limited because of harsh climatic conditions, inaccessible areas, and international border conflicts. In the last few decades, satellite-based remote sensing has emerged and evolved as a powerful alternative to overcome the limitations of a field-based approach. The remote-sensing approach makes use of optical sensor-based photogrammetry and radar sensor-based interferometry techniques in order to map the topography of the Earth’s surface. Two such measurements at different times result in the surface elevation change.
Glacier ice melt reduces glacier elevation, whereas ice mass gain leads to positive glacier elevation change. Ice density (900 kg/m3) and elevation change measurements are used to estimate glacier mass change. A fraction or entire glacierized catchments of the Karakoram-Himalaya is often cloud covered because of well known rapidly changing weather conditions of the high mountains. Therefore, optical remote sensing cannot map those cloud covered regions.
Two recent studies (1,2) make use of two global radar digital elevation models (DEM) to provide glacier elevation and mass changes of 3700 glaciers of the Karakoram-Himalaya during 2000-2012. The first elevation model is a result of NASA’s (National Aeronautics and Space Administration) Shuttle Radar Topography Mission (SRTM) carried out during February 11-22, 2000. The SRTM DEM is an open-source, near-global dataset.
The second elevation model was generated by Saurabh Vijay and his team at the Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany. They used radar images of the year 2012 of the TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) and processed them using standard bistatic radar interferometry. The TanDEM-X is an ongoing space-borne radar mission launched by German Aerospace Center (DLR) in 2010.
The studies (1,2) found that the Himalayan glaciers lost more mass compared to the glaciers in the Karakoram during 2000-2012. The sub-region, called Lahaul-Spiti of the Himalayas, lost most ice mass amongst three regions investigated in the studies (Figure 1). The potential reason behind this variability is that the Himalayan glaciers receive precipitation by Indian summer monsoon during summer months, whereas Karakoram glaciers are more influenced by mid-latitude westerlies in the winters. Consequently, the Karakoram glaciers are more stable than the glaciers of Himalaya.
Figure 1: Map of mountain ranges of high-mountain Asia showing the major rivers (light blue polylines). Three rectangles indicate the three regions, called Lahaul-Spiti and JK West of the Himalaya and JK East of the Karakoram. The values are mean surface elevation change (m/yr) estimated over the 2000-2012 period. Adapted from the Remote Sensing article: https://doi.org/10.3390/rs8121038
Apart from these external factors of regional glaciers changes, these studies (1,2) investigated the role of debris cover, supraglacial lakes, and ice cliffs on glacier elevation changes. Mountain glaciers are often debris-covered due to eroding slopes, avalanches, and the emergence of englacial debris. The debris, if thick enough, can protect the ice beneath from incoming shortwave (solar) and long-wave radiations. On the contrary, thin debris cover, supraglacial lakes, and ice cliffs can absorb more radiation and foster ice melt, leading to high negative glacier elevation change. The studies (1,2) investigated 113 large glaciers and found out the significant role of debris insulation in case of 32 glaciers. The role of supraglacial lakes and ice cliffs appeared to be prominent in the case of 16 other glaciers.
The Karakoram region is well known for surge-type glaciers. Glacier surge is a short-lived event (few days to months) where a glacier flows significantly and advances substantially. During surge events, the glacier ice from upper catchments transports to the down-glacier areas. In the past, such events have caused natural disasters like glacial lake outburst floods and influenced the course of rivers flowing from the glaciers. This threatens the living community. The glacier-wide surface elevation change from remote sensing shows the kinematic wave (negative-positive elevation) like structure on the glacier surface, which can help to detect the surge event. The high spatial details of the measurements by (2) helped to map 29 surge-type glaciers, which 16 of them never reported before due to limitations of data and techniques.
In short, these studies have made use of modern satellite technology to measure early 21st-century glacier elevation and mass changes with very high details and to better understand the links of their changes with system inherent and external factors.
These findings are described in the article entitled Elevation change rates of glaciers in the Lahaul-Spiti (western Himalaya, India) during 2000-2012 and 2012-2013, recently published in the journal Remote Sensing, and the article entitled Early 21st century spatially detailed elevation changes of Jammu and Kashmir glaciers (Karakoram-Himalaya), recently published in the journal Global and Planetary Change. This work was conducted by Saurabh Vijay from the Friedrich-Alexander-Universität Erlangen-Nürnberg and the Technical University of Denmark, and Matthias Braun from the Friedrich-Alexander-Universität Erlangen-Nürnberg.
References:
- Vijay S. and Braun, M. Elevation change rates of glaciers in the Lahaul-Spiti (western Himalaya, India) during 2000-2012 and 2012-2013, Remote Sensing, 8, 1038, doi: 10.3390/rs8121038
- Vijay, S. and Braun, M. Early 21st century spatially detailed elevation changes of Jammu and Kashmir glaciers (Karakoram-Himalaya), Global and Planetary Change, 165, 137-146, doi: 10.1016/j.gloplacha.2018.03.014.