Region-wide glacier mass budgets and area changes for the Central Tien Shan between ~Â 1975 and 1999 using Hexagon KH-9 imagery

The geodetic mass budget estimates for a glacierized area of 5000 km2 revealed increasing mass loss east to west and from the inner to the outer ranges. Highest mass loss accompanied by the most pronounced glacier retreat was found for the Ak-Shirak massif with a region-wide mass balance of − 0.51 ± 0.36 m w.e. a− 1 and a rate of area change of − 0.27 ± 0.15% a− 1, whilst moderate mass loss was observed for the Inylchek (0.20 ± 0.44 m w.e. a− 1) and Tomur area (0.33 ± 0.30 m w.e. a− 1) despite partly debris cover. These latter regions also revealed the lowest glacier shrinkage within the entire Central Tien Shan. The total glacier mass loss of 0.35 ± 0.34 m w.e. a− 1 is, however, within the global average whilst the glacier area shrinkage is comparatively low. On average, the investigated glacierized area of ~ 6600 km2 shrank by 0.11 ± 0.15% a− 1 only. We could also identify several surge-type glaciers. The results are consistent with in-situ mass balance measurements for Karabatkak Glacier and previously published results of the Ak-Shirak range proving the suitability of declassified imagery for glacier change investigations. The contribution to the runoff of Aksu River, the largest tributary of the Tarim River, due to glacier imbalance has been determined at ~ 20% for the 1975-2000 period.