Variations On Equilibrium Linealtitude Of The Glacier No.1at The Headwaters Of Urumqi River, Tianshan, China

Glacier is the indicator of climate change. As global warming in the20th century,mountain glaciers become very sensitive to climate change. Glaciers all over theworld showed an accelerated melting trend glacier equilibrium line altitude(ELA)increased since the end of the Little Ice Age, The ELAis a theoretical line on a glacierat which annual mass accumulation equals annual mass loss. The glacier ELA is oneof the important parameters reflecting climate change. Glacier behaviors such asadvancing or retreating are controlled by the variations in ELA. Relative to its steadystate, a glacier advances when its ELA falls, retreats when its ELA rises, or meltsentirely when its ELA rises above its summit. In contrast to variations in glacierlength or area, variations in ELA respond almost simultaneously to climate change.Therefore, studies on ELA variations and their sensitivity to climate change areimportant for understanding correlations between glacier behavior and climate change.This study is based on the observation data of the Glacier No.1at the headwaters ofUrumqi River in the Tianshan Mountains during the period1959-2010, the variationcharacteristics of the Equilibrium Line Altitude (ELA) are analyzed. Furthermore,statistical relationship between ELA and air temperature and precipitation isestablished. The study analyzed the climatic sensitivity of the ELAabout Glacier No.1at the Headwaters of the Urumqi River nearly52years. The results indicated that:(1) In the period1959-2010, the glacier ELA showed a general increasing trend,with the interannual trend rate of8.4m/10a, in other words, the glacier ELA showedan increased tendency with the value of about45m for the entire period. The ELArised slowly in1960s, then declined in1980s, sharply increased in the middle1990s,reaching the highest altitude of4192m a.s.l.in2008. But the remarkable of these wasthat the ELA decreased sharply in2009, which the impossible cause was theappearing of mass balance increasing.(2) Analyzing the ELA variability and mass balance of Urumqi Glacier No.1inthe past52years, the Urumqi glacier No.1ELA varied from3875to4192m a.s.l,with the mean value of4053m a.s.l.. The ELA in positive mass balance year was102m lower than that in negative mass balance year. Significant negative correlation was existed between the ELA and annual net mass balance, and the ELA was4018mwhen the glacier was at the steady state.(3) The ELA variability of of Urumqi Glacier No.1was influenced by summertemperature and summer precipitation, but summer temperature was the main climaticfactor. The climatic sensitivity research of the ELA showed that the ELA ascends ordescends by64m if summer temperature increases or decreases by1°C, and ELAascends or descends by21m if summer precipitation decreases or increases by100mm.(4) By contrasting the research results of Urumqi Glacier No.1with the rest ofthe world region glaciers findings, Urumqi Glacier No.1expresses slower response toclimatic factors (the major is precipitation and temperature) than any others. As otherglaciers are in the marine climate or near a marine climate conditions, and UrumqiGlacier No.1is in continental climate conditions, they reflected the difference ofprecipitation and temperature, which may represent the different properties of theglaciers on climate response between marine glaciers and continental glaciers.