The responds of the Western Pamirs alpine lakes to climate change (Lake Lower Varshedzkul case study, Gorno-Badakhshan Autonomous Region, Tajikistan)

Glacial degradation of Pamir, growth of alpine lakes area, of stream discharges, frequency and risk of natural disasters are all results of increasing summer temperatures. The influence of climate change on the growth of the potential risk of outburst floods and debris flows in the Western Pamirs has been proved, using the example of a typical glacial basin of the Varshedzdara River (the Gunt River tributary). Detailed field studies of the basin, including bathymetric and aerial surveys, revealed the instability of the unconsolidated moraine impounding Lake Lower Varshedzkul, the presence of an ice core in it, and the presence of active rock stream, a large amount of material potentially involved in debris flow, in the river valley. Estimated volume of water contained in lakes Lower Varshezkul and Higher Varshezkul are 1.94 million m³ and 3.57 million m³ respectively. The area of glacial lakes in the Varshedzdara river basin has increased 3 times over the past 40 years (from 51.7 tsd m² to 173 tsd m²), and the area of the Varshedz glacier has decreased by 11% (from 7 mln m²  to 6.2 mln m²). The maximum volume of a debris flow in the valley was estimated at 5.73 mln m³, the debris flow discharge was 1000 m³/s. If both lakes are to breach simultaneously, an estimated discharge would reach 3.725 mln m³. That includes half of the volume of Higher Varshezkul and the entire volume of Lower Varshezkul lakes. According to the results of mathematical modeling, it was found that the lag time for the stream reaching the settlements is only 0.1 h, the buildings and the highway located on the debris cone will be inundated up to 3–4 meters with flow velocity of 3 m/sec. and destroyed. The results can be interpolated to other glacial basins of the western Pamirs, in which growing glacial lakes are located, and the potential hazard will increase.

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