Glacier retreat and debris cover evolution in the Afghan Hindu Kush Himalaya between 2000 and 2020

Glaciers play a crucial role in the hydrological cycle, providing water in summer when it is most needed for irrigation. Global warming is leading to glacier retreat and enhanced summer runoff in the short-term, which should occur until glaciers become small enough that there is an end to this glacial subsidy and a reduction of summer runoff. However, debris accumulation, as it may alter the surface energy balance, will modify the rate at which this happens and may represent an important negative feedback. For this reason, quantifying and explaining glacier change in the Hindu Kush Himalaya (HKH) region, notably its relation to changing debris cover, is of paramount importance, especially for a country like Afghanistan with water resources highly dependent on glacial meltwater. This study assessed changes in glaciers of Afghanistan using data for 2000, 2007, 2017 and 2020 based upon the analysis of country-wide Landsat data and innovative indices for mapping both ice and debris-covered glacier extent.

Results showed 2862.5±47.8 km² of total glacier area in the year 2000, decreasing by 45.9 km²to 2007 (i.e. 6.55 km² per year), by a further 112.0 km² by 2017 (i.e. 11.2 km² per year), and by a further 73 km² (i.e. 24.3 km² per year) by 2020; that is there is a progressive increase in retreat rates. Of the 231.2 km² (8.07 %) loss of glacier surface area between 2000 and 2020, almost 81% related to glaciers with a size ≤ 2.01 km², which accounted for 50% of the total glacier area in the year 2000. Decreases were more dominant in center and northern regions of the country, whilst the northeastern region, the most glaciated part of the country, showed lesser changes. Increases in total debris cover area were found in the northeastern region of the country where there were lower decreases in total glacier area, whilst there were noticeable decreases in total debris cover area observed in southern and southeastern regionss and higher decreases in total glacier area. This suggested that the ability of the glaciers to produce debris cover has regional significance in explaining whether glacier loss occurs.

Ice elevation significantly changed over the time; changes in minimum ice elevations were up to +53 m, higher in the north, south, and southeastern regions. Maximum ice elevations decreased by -88 m, suggesting loss of accumulation zones. However, the northeastern part had a positive increase in maximum accumulation zone heights +23 m, this indicates possibility of increases in accumulation area.  

These results revealed differences in the regional response of Afghan glaciers to climate change. In the next stage of this work, we will link the spatial distributions of glacier response to downstream populations to identify those regions most exposed to the effects of these climate changes.