Mass-balance observations and reconstruction for Haxilegen Glacier No.51, eastern Tien Shan, from 1999 to 2015

Haxilegen Glacier No.51 (43.731 degrees N, 84.391 degrees E; CN5Y741C0051) is located in the Kuytun river basin, Erenharbirga range, eastern Tien Shan. This study presents the annual mass balance of Haxilegen Glacier No.51 for 7 hydrological years and uses a temperature-index and an accumulation model to reconstruct the annual mass balance from 1999 to 2015. The model is calibrated against annual altitudinal mass-balance measurements and then applied to the period with no measurements. We find an accumulated mass balance of -6.06 +/- 0.88 m w.e.a(-1) over the period of 16 hydrological years, with an average annual value of -0.32 +/- 0.22 m w.e.a(-1). The mean glacier-wide annual, summer and winter balances for 1999 to 2015 are -0.37, -0.54 and 0.16 +/- 0.22 m w.e.a(-1), respectively, with a high correlation coefficient (r = 0.95, p < 0.001) between annual balance and summer balance. The calculated mass-balance sensitivity of the glacier to temperature is -0.51 m w.e.a(-1) degrees C-1 and to precipitation is 0.08 m w.e.a(-1) for a 10% increase. The sensitivity of seasonal mass balance indicates that temperature during the melt season (May-August) and annual precipitation are the major contributors to mass-balance fluctuation.