近52a天山乌鲁木齐河源1号冰川平衡线高度及其与气候变化关系研究

论文以天山乌鲁木齐河源1号冰川1958/1959—2009/2010年平衡线高度观测资料为基础,研究了平衡线高度及其与气候变化的关系。结果表明,在研究时段内,平衡线高度变化分为正常波动、缓慢下降、迅速上升三个阶段,变化范围介于3 948~4 484 m,多年平均为4 067 m,总体呈普遍上升趋势,总计上升了90 m,且在2009/2010年超过了冰川的上界,意味着该年度冰川全部处于消融状态。积累区比率作为平衡线高度变化的一个重要指标,在这一时期内也呈现明显的下降趋势,下降了约17%。物质平衡与平衡线高度具有显著的负相关性,物质平衡减小100 mm,平衡线高度将上升17 m。冰川处于稳定状态时的平衡线高度,即零平衡高度ELA0为4 018 m。平衡线高度随纯消融量的增加而升高,纯消融量增加10×104m3,平衡线高度上升14 m。平衡线高度对气候变化的敏感性研究表明,如果夏季平均气温升高1℃,则平衡线高度将上升约82 m,如果年降水量增加100 mm,则平衡线高度将下降约41 m,且夏季气温是影响冰川平衡线高度变化的主导气候因素。

Study on Equilibrium Line Altitude and Its Relationship with Climate Change of Urumqi Glacier No.1 in Tianshan Mountains in Recent 52 Years

Urumqi Glacier No.1 is located at the headwaters of the Urumqi River in eastern Tianshan, it is one of the ten reference glaciers around the world in World Glacier Monitoring Service (WGMS). It is considered as a key element of the system because of its special geographical position in arid Central Asia. As a reference glacier in the WGMS glacier monitoring network, it provides the longest glaciological and climatological monitoring record in China. Equilibrium line altitude (ELA) is defined as the altitude where the annual mass balance is zero. Glacier behaviors such as advancing or retreating are controlled by ELA variations, and fluctuations of ELA provide an important indicator of glacier response to climate change. In practice, the ELA is a narrow zonal area, and not very easy to be identified on the glacier surface, therefore, the determination of ELA is mainly done based on the contour map of the annual mass balance of the whole glacier. This paper, based on ELA data of Urumqi Glacier No.1 during 1959-2010, studies the changing process and characteristics of ELA. The results show that ELA experienced three phases during the whole observation period. ELA presented a slow ascending trend in a normal fluctuation range before 1986, with a mean of 4051 m a.s.l; it descended slowly from 1986 to 1996, with a mean of 4035 m, however, it ascended promptly since 1997, with a mean of 4125 m. In 2010, the highest ELA was observed which surpassed the glacier summit, implying that the whole glacier was ablating in this year. During the study period, ELA range was between 3948 m and 4484 m, with a mean of 4067 m, and the general tendency was ascending continually, ascended about 90 m. Accumulation area ratio (AAR) as an important indicators of the ELA change showed obvious decreasing trend, descended by 17%. Analysis shows mass balance and ELA has significant negative correlation. When mass balance decreased by 100 mm, ELA would ascend 17 m and glacier ELA was in a steady state, namely zero ELA (ELA₀) would be 4018 m. As the net ablation increases, ELA shows an ascending trend. Data analysis shows when net ablation increased 10×10⁴ m³, ELA would ascend 14 m. Analytical results of the ELA sensitivity response to climate change suggest that every 1 ℃ summer temperature increase would lead to 82 m ELA ascendance, and ELA would descend 41 m when annual precipitation increased 100 mm. According to the difference of ELA sensitivity in response to summer temperature and precipitation, ELA ascendance was controlled mainly by summer temperature.