Influence of Degree-Day Factor Variation on the Mass Balance of Glacier No. 1 at the Headwaters of Ürümqi River, China

The degree-day factor (DDF) is a key parameter in the degree-day model, and the variations in DDF have the significant effects on the accuracy of glacier mass balance modeling. In this study, Glacier No. 1 at the headwaters of Ürümqi (乌鲁木齐) River in China was selected, and the estimated DDF by stakes-observed mass balance and meteorological data from 1983-2006 was used to analyze the spatio-temporal variability of DDF and its influencing factors, such as climate condition, surface feature, and topography. Then, the ablations from the 1980s to 2000s were estimated using the degree-day model, and the ablation change from the 1980s to 2000s was divided into the changes caused by climate change and by the ice-surface feature. The following results were obtained: (1) The annual change in DDF for snow was not obvious, whereas that for ice increased, and the increasing trend on the lower glacier was more significant than that on the upper glacier because of decreased albedo caused by variations in ice-surface feature; (2) The DDF for ice clearly decreased with altitude by approximately 0.046 and 0.043 mm·℃⁻¹·d⁻¹·m⁻¹ on the east and west branches, respectively, and the DDF of the west branch was obviously larger than that of the east branch in the same altitude belt; (3) the changes in mass balance in the summers from the 1980s to 2000s were −391 and −467 mm on the east and west branches, respectively. Among the total changes, the components directly caused by climate change were −193 and −198 mm, whereas those indirectly caused by ice-surface feature change were −198 and −269 mm on the east and west branches, respectively.