Study On Mass Balance And Its Relationship With Climate Change Of Urumqi Glacier No.1in Tianshan Mountains, China

The rapid ablation and retreat of mountain glaciers in the20th century has beenoccurring on a global scale, and the significant accelerating trend has appeared duringthe past two or three decades. As a link connecting changes of glaciers with thechanges of climate, glacier mass balance is directly linked to glacier fluctuations,climate change and also directly reflects changes of glacier volume, melting andrunoff. It is important to assess the response of mass balance to climate change.Urumqi Glacier No.1(at headwaters of Urumqi River), the best monitoredglacier in China, it is one of the ten reference glaciers around the world in WorldGlacier Monitoring Service. Based on the mass balance and climate observation datafor1959–2010, study on the mass balance and its relationship with climate change,results show that mass balance decreased rapidly, equilibrium line altitude ascendedsignificantly, accumulation area ratio decrease obviously, net ablation enhancementconstantly, and glacier terminus retreated continuously in response to climate change.(1) Mass balance decrease rapidly. Mass balance varied between–1327and374mm, with a mean of287mm/a, cumulative mass balance was14883mm,equivalent to glacier thinning of16.5m. Mass balance can be grouped into threeperiods: mass loss is not serious before1985; weak negative balance for1985–1996;accelerated mass loss since1997, with a mean of691mm/a, only is a weak positivebalance in2009(63mm), and the minimum value was1327mm emerges in2010.During1997–2010, cumulative mass balance was9676mm, accounting for65%ofthe total mass losses in26%of the time, summer balance increasing promptly since1997, which directly causes the accelerated mass loss. For1962–2010, it has melted24.2%of ice volume, provides the glacier runoff was2883.4×104m3for this region.(2) Equilibrium line altitude (ELA) ascended significantly. ELA showed asignificant ascending trend, ascended about90m. ELA presented slowly ascendedtrend in a normal fluctuation range, with a mean of4051m before1985, then,descended slowly, with a mean of4035m, however, it ascended promptly since1997,with a mean of4125m, until2010, ELAsurpassed the glacier summit, implies that thewhole glacier was ablating. ELAand mass balance has significant negative correlation, the steady state ELAwas4018m, mass balance gradient was5.9mm/m.(3) Accumulation area ratio (AAR) decrease obviously. AAR showed obviousdecreasing trend, descended by17%, AAR and mass balance has significant positivecorrelation, AAR synchronously changed with mass balance result. The steady stateAAR was56%, higher than the mean AAR (46%), indicated that the glacier in aretreat state at present.(4) Net ablation enhancement constantly. As the summer temperature increases,net ablation of glacier shows an increases trend, summer temperature increasesdirectly enhances the glacier melting. The net ablation is more sensitive to massbalance and ELA change, analysis shows that net ablation increases50×104m3, massbalance decrease400mm, ELAascends70m.(5) Glacier terminus retreated continuously. Terminus has retreat by139.7mduring19621993, from1993to2010, the east branch retreated by59.6m, and thewest branch retreated by101.6m. The retreat speed of the west branch terminusapparently quickens more than the east branch.Urumqi Glacier No.1is a summer-accumulation-type glacier, mass balance wasmainly affected by annual precipitation before1986, however, it is mainly controlledby the summer temperature since1986. Analyzed the mass balance sensitivityresponse to climate change, results suggest that1°C summer temperature increasesleads to445mm mass balance decrease, and increases141mm when annualprecipitation increases100mm, and suggest that mass balance decrease wascontrolled mainly by summer temperature.Three mechanisms can be explaining the accelerated mass loss of UrumqiGlacier No.1since1997. The first is abnormal rise of air temperature, especially, airtemperature appeared abnormal rise since1997. The second is the ice temperature rise.The third is the albedo reduction of the glacier surface, the main cause includes thatthe continued increases of the ablation area, and high concentration of organic mattersand microorganisms.