Assessment of Glacial Area and Volume Change in Tien Shan (Central Asia) During the Last 60 years Using Geodetic, Aerial Photo, ASTER and STRM Data

The water-issue problems that occur during times of persistent drought are extremely important for central Asia. Despite the presence of large deserts and prairies with very low precipitation and extremely dry climates, central Asian mountains hold one of the greatest concentrations of perennial snow and ice in the mid-latitudes and constitute a vital source of water for more then 100,000,000 people living in this region. This research aims to evaluate glacial area and ice volume changes using aerial photographs from 1943, 1977, and Satellite Remote Sensing data from 2000/2003 over the Akshiirak ice-fields and Ala Archa glacierized basin in the central and northern Tien Shan to understand changes in the glacier water resources of central Asia during the last 60 years. These data were converted from WGS-84 to STRM and then to the Pulkovo 1942 (Russian) coordinate system using a 7-parameter Helmert transformation method. For vertical validation, the STRM DEM was compared to a DEM constructed with additional 5 m and 10 m contour lines digitized from 1:25000 topographic maps for low-relief, non-glacial areas. Glacier boundaries were digitized from an ASTER L1A image acquired on August 18, 2003 and orthorectified using Orthobase digital photogrammetric package with 9.5 m RMSE of 28 ground control points. To delineate glaciers in problem areas, resulting from debris-covered termini and shadows, thermal bands and true hardware-enabled stereo viewing with nadir 3N and backward-looking 3B bands was used. Digitizing accuracy of the 2003 glacier boundaries was verified from GPS field measurements of 7 glacier termini in 2002. For surface elevation comparison, a second DEM was generated from 10 m contour lines for all glaciers (424 km²) using 16 topographic maps of 1:25000 scale that were created using the aerial photographs of 1977. In 1943, the glaciers of the Akshiirak massif covered 424.7 km² and 42.8 km² in the Ala Archa glacierized basin. From 1943 to 1977, the glacial area shrunk to 406.8 km² (4.2%) in Akshiirak, and to 40.6 km² (5.2%) in Ala Archa Basin. From 1977 to 2003, glacial recession reached 8.6% in the Akshiirak massif and 10.5% in the Ala Archa Basin. During the last 60 years ice volume of the Akshiirak glaciers was reduced on 10 km³. However, the overall trend of glacier recession is variable: while 150 glaciers in Akshiirak were significantly reduced, 24 glaciers increased their volume by 1.8%. According to the Russian military geodetic data and aerial photographs the Akshiirak glaciers have retreated up to 3 km from 1869 to 1943, with surface elevation decreasing 50-80 m.