Elevation change of Fedchenko Glacier, Pamir Mountains, from GNSS field measurements and TanDEM-X elevation models, with a focus on the upper glacier

Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3-4 m in the high accumulation regions. The seasonal elevation changes reach up to +/- 5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928-2000, resulting in peak values of 1.5 m a(-1). Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between -0.2 and -0.4 m a(-1) from 2009 to 2016. The estimated glacier-wide mass-balance rates are -0.27 +/- 0.05 m w.e. a(-1) for 2000 to 2011 and -0.51 +/- 0.04 m w.e. a(-1) between 2011 and 2016.