Rapid decrease of observed mass balance in the Urumqi Glacier No. 1, Tianshan Mountains, central Asia

The mass balance of Urumqi Glacier No. 1 located in Tianshan Mountains of central Asia has been monitored since 1959. Based on the long-term climate and glacier mass balance observation data for the period 1959–2010, analyses show that the glacier mass balance has decreased rapidly, the equilibrium line altitude (ELA) has ascended significantly and the glacier terminus has retreated continuously in response to climate change. The cumulative mass balance was −14,883 mm w.e., equivalent to glacier thinning of 16.5 m, with a mean value of 0.32 m/y. The ELA showed a significant ascending trend, ascending about 90 m. The averaged ELA was 4067 m a.s.l., and analysis shows the steady-state ELA (ELA0) was 4018 m a.s.l., with the mass-balance gradient α = 5.9 mm/m. The glacier terminus retreated by 199.3 m at the east branch and 241.3 m at the west branch. Linear regression analysis results suggest that 1 C° summer temperature increases leads to 440.6 mm mass balance decrease. Mass balance increases by 120 mm when annual precipitation increases by 100 mm. Mass balance decrease was controlled mainly by summer temperature. If such increased warming continues in the future, the glacier mass balance will form a strongly negative balance, the glacier will shrink, and the glacier terminus will continue to retreat.