Mass balance and recession of Urumqi glacier No. 1, Tien Shan, China, over the last 45 years

Observations of Urumqi glacier No. 1 at the headwaters of the Urumqi river, Tien Shan, show remarkable changes between 1959 and 2003. The cumulative mass balance of the glacier is -10 032 mm, equivalent to 11.1 m of glacier ice, or 20% of the glacier volume, showing particular sensitivity to temperature change. The speed of glacier flow has gradually declined, especially since the 1980s. From 1980 to 2003, the flow speed of the east and west branches of the glacier decreased by about 21% and 43%, respectively. The glacier continuously retreated from 1962 to 2003. its length has decreased by about 180 m (7.5%) and its area has diminished by 0.23 km(2) (11.8%). Analyses show that summer precipitation is negatively correlated with mass balance and positively associated with runoff. These relationships are reasonable, as higher precipitation leads; to higher runoff and lower glacier melt. On the other hand, summer temperature is negatively correlated with mass balance and positively associated with runoff, as higher temperatures lead to higher glacier melt and thus higher runoff, with summer temperatures controlling mass-balance variation. Over the past 45 years the negative mass balance, caused by higher ablation than accumulation, is associated with precipitation increase and temperature warming over the study area.