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18 Aug 2020 | Cryosphere

Larger glaciers in the Hindu Kush are behaving like glaciers in the Karakorum

Sher Muhammad & Chimi Seldon

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Location and topography of the Chitral River basin superimposed by glacier cover (in blue), studied glaciers (in red), streamline, weather stations, and Chitral River flow gauge station. (Source: ICIMOD, 2020)

Findings from a recent study show that the larger glaciers in the Hindu Kush region of Pakistan are relatively stable and are behaving similar to the glaciers in the Karakoram. This is an interesting finding since glaciers in the region were previously found to be losing mass significantly.

Our colleague Sher Muhammad was a co-author of the study, which focused on six large glaciers, all greater than 20 sq. km, in the Chitral Valley, Pakistan, which is situated in the Hindu Kush region. There is a dearth of data on glaciers in the valley in comparison with that on glaciers in the rest of the Himalaya and Karakoram.

The authors used remote-sensing elevation and satellite images from 2001 to 2018. They observed a general retreat with gradual upward shifting of the equilibrium line altitude (ELA) at a rate of ~13 m.a−1 on average, which is comparatively less. The glaciers are losing mass at an average rate of 11 cm (water equivalent) per year. These glaciers are retreating, but at a lower rate. The mass loss of glaciers during the study period was potentially influenced by the local climatic condition of each glacier as well as differences in topographic features and location.

Previous studies (such as that by Ahmad et al., 2018) on seasonal data had indicated a warming trend in the area, which may explain the spatial changes in glacier parameters; however, this particular research did not observe such trends in climatic data. The overall trends may be similar to other glaciers of the Chitral River basin but need more detailed on-field and remote-sensing studies. These glaciers need continuous assessment given their regional importance as major sources of water and their associated hazards.

The authors use a set of threshold values found during the estimation of ELA and snout position using three normalized differences in glacier index, snow index, and debris index. Since the threshold values for the identification of ELA and snout position vary from region to region, this study may be further used for this region and similar data for future glaciological studies.

ELA and its role in understanding glacier melt

The ELA is the average elevation of the zone where the accumulation and ablation are equal. It is related to the local climate, particularly winter precipitation and summer temperature. Variations in the ELA can be attributed to changes of these two variables. If the annual mass balance of the glacier as a whole is negative, the ELA rises, and when the balance is positive, the ELA falls. When the state of the ELA is steady, annual net balance is zero, as the glacier mass and the geometry are in balance with climate.

Hence, the ELA is a parameter for estimating accumulation area ratio where the ratio of accumulation area and total area is calculated. Since there is a very close connection between the ELA and local climate, the ELA is an important indicator of glacier response to climate change. This is crucial for understanding glaciers, which are important indicators for global climate and serve as an important water resource but are also extremely vulnerable to climate change.

How glaciers respond to climate change in the Hindu Kush

Usually, the response time of large glaciers (length of time taken for a glacier to adjust its geometry to a new steady state after a change in glacier mass balance) is long in contrast to small glaciers, which are generally more prone to climatic changes because of their shorter response time. In addition, many previous studies have also shown that glaciers with thick debris cover have unpredictable response to temperature increase due to the insulation properties of debris, with variable rate depending on the debris thickness. So, the present-day (up to the last few decades) climate change impact may be seen only in the coming decades (15–100 years). A comparative assessment of small and large glaciers in the Hindu Kush region may help understand their response to the contemporary climate change.

Terminus retreat of all six glaciers in the study area between 2001 and 2018
Terminus retreat of all six glaciers in the study area between 2001 and 2018

 

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