A long-term health check
At the headwaters of the Urumqi River, scientists at the Tianshan Glaciological Station have maintained one of the world's longest and most detailed health charts for a glacier. The subject is Urumqi Glacier No. 1, a valley glacier that has been under continuous observation since 1959. This extensive record makes it an reference point for the World Glacier Monitoring Service. Researchers here track the glacier's "mass balance," an annual accounting of ice accumulation from snowfall versus ice loss, known as ablation, from melting.
The data reveals a persistent and accelerating decline. Between 1959 and 2010, the glacier's mass balance showed a decreasing trend of -14.5 mm per year. The loss has intensified dramatically in recent decades. One study noted that the average mass balance was -136.4 mm per year between 1959 and 1996, but this loss jumped to -663.9 mm per year from 1997 to 2010. From 1962 to 2018, the glacier's total area shrank by 19.3%. The rate of this shrinkage after 1994 was about three times faster than in the period between 1962 and 1986. The accelerated melt is linked to rising summer temperatures. The glaciers in the wider Eastern Tian Shan region lost 22% of their area between 1990 and 2015.
A glacier divided
A dramatic event in the glacier's recent history occurred in 1993, when decades of negative mass balance and thinning ice caused it to split into two separate east and west branches. This separation exposed more of the glacier's front to warmer temperatures, which further quickened the melting process.
The Bogda Shan range, where the glacier is located, saw an average decrease in glacier surface elevation of 11.6 meters between 2000 and 2017, corresponding to a rate of 0.68 meters per year. The entire Urumqi River Basin lost a total of 1.76 cubic kilometers of ice volume between 1964 and 2021. The meltwater from these glaciers is a primary water source for the region, feeding major rivers like the Urumqi and Tarim. The ongoing loss of ice from these "water towers" of Central Asia poses challenges to the long-term water security for the arid and semi-arid regions downstream. Projections estimate that under current climate scenarios, the glacier could completely disappear within the next 50 to 90 years.