Glacier changes in the Big Naryn basin, Central Tian Shan

A glacier inventory referring to the year 2007 was created for the Big Naryn basin based on satellite imagery. The 507 glaciers had a total area of 471 km². Compared to the Soviet glacier inventory based on data from the mid 20th century, the total glacier area decreased by 23.4%. The shrinkage varies from 14% to 42% between individual mountain ranges. We discuss the possible causes for this considerable variation by analyzing and interpreting topographic parameters and differences between seven sub-regions.On three glaciers, ice thickness was derived by ground penetrating radar (GPR) measurements on the glacier tongues and by surface slope using a simplified ice mechanical approach on the upper parts. We estimate the total ice volume of the basin for both inventories using volume–area scaling. Our results show a current glacier volume of 26.0–33.3 km³. A total of 6.6–8.4 km³ (20%) have been lost since the mid 20th century. The water equivalent of 5.9–7.6 km³ was transformed into excess discharge and contributed to at least 7.3–9.2% of total runoff in the considered period.

► 507 glaciers with a total area of 471 km² existed in the Big Naryn basin in 2007.
► Since the middle of the 20th century, the total glacier area decreased by 23.4%.
► During the same time, the ice volume was reduced by 20% to a current total of 26.0–33.3 km³.
► The excess discharge contributed to at least 7.3–9.2% of total runoff.