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

The meltwater released by the glaciers in the Central Tien Shan feeds in particular the Tarim River which is the main artery for the oases at the northern margin of the Taklamakan desert. The correct assessment of the contribution of the glaciers' meltwater to the total runoff is hampered by the lack of long-term measurements of glacier mass budgets. Digital terrain models (DTMs) for the different regions in the Central Tien Shan were generated based on ~. 1975 KH-9 Hexagon imagery and compared to the SRTM3 DTM acquired in February 2000. Moreover, glacier area changes for the period ~. 1975-2008 have been measured by means of multi-temporal optical satellite imagery. The geodetic mass budget estimates for a glacierized area of 5000km² 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±0.36mw.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±0.44mw.e.a^-1) and Tomur area (0.33±0.30mw.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±0.34mw.e.a^-1 is, however, within the global average whilst the glacier area shrinkage is comparatively low. On average, the investigated glacierized area of ~6600km² 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.