Study Of Mass Balance Change Of Laohugou Glacier No.12 In Qilian Mountains Based On Glacier Melt Models

Glaciers play an important role in regulating the climate and hydrology of the Earth system.Glacier mass balance（MB）is one of the important variables in the monitoring of climate and hydrological systems.The long-term MB series is of great significance for the assessment of meltwater runoff and the understanding of the interaction between glaciers and the atmosphere.To explore the change of glacier MB in the western Qilian Mountains,the Laohugou Glacier No.12（LHG12）was selected as the research object,the measured data were used to calibrate the model parameters,and the reanalysis dataset was used as input data to drive the distributed Simplified Energy Balance model（SEB model）and the Enhanced Temperature Index model（ETI model）to reconstruct the MB series of LHG12 from 1980 to 2020.Combined with the reanalysis dataset,the characteristics of local climate change were analyzed,and the relationship between the change of glacier MB and climate was discussed.At the same time,the influence of large-scale circulation and teleconnection on glacier MB was explored.The main conclusions of this thesis are as follows:（1）From 1980 to 2020,the annual MB of LHG12 showed an overall downward trend,and the glacier loss state intensified.The reconstruction results of the two models are very close and have the same change trend.After time and space verification,the performance of the SEB model is slightly better than that of the ETI model.The results of the SEB model simulation show that the annual MB of LHG12 is-0.39±0.28 m w.e.a^-1 and the cumulative MB is-16±4 m w.e..The winter MB was relatively stable and the summer MB showed an obvious downward trend consistent with the annual MB.Since 1990,LHG12 has been melting more rapidly,and the rate of mass loss has increased by two times compared with 1980-1990.2001-2010 was the decade with the most serious mass loss in summer and the whole year.The equilibrium line altitude has fluctuated and increased at the rate of 37.5 m/10a since 1980.The changing trend of the accumulation area ratio is opposite to the equilibrium line altitude,and its retreat rate is about5.5%/10a.（2）The MB decreases with the increase in altitude,which indicates that the MB is mainly affected by temperature.There is a slight difference in the spatial simulation results between the SEB model and the ETI model.The SEB model simulates more melt at the end of the glacier,while the ETI model simulates more melt at high altitudes.The main reason is that the structural differences between the two models lead to different conditions for controlling the melting.The melting condition of the ETI model is that the temperature is greater than 0℃,which is only controlled by the air temperature.In the SEB model,the melting condition is that the melting energy₈8))is greater than 0,which is controlled by temperature and shortwave radiation.（3）The climate sensitivity test shows that the LHG12 is the most sensitive to temperature change.The results of the SEB model show that when the temperature changes to+1℃,the MB sensitivity is-0.51 m w.e.a^-1.LHG12 is less sensitive to precipitation,with precipitation+10%resulting in MB+0.09 m w.e.a^-1.The MB sensitivity to the incoming shortwave radiation differs greatly between the SEB model and the ETI model,which are-0.30 m w.e.a^-1 and-0.08 m w.e.a^-1,respectively,mainly due to the difference in the model structure.（4）In the past 40 years,LHG12 has been in a state of increasing temperature and precipitation.There is a good correlation between glacier MB and air temperature.With the rise of air temperature,glacier mass loss increases.An increase in precipitation does not increase the mass accumulation,because rising temperature increases the proportion of rainfall in precipitation.The analysis of 500 h Pa geopotential height field and wind field show that the 500 h Pa geopotential height over the Tibetan Plateau increased from 1991 to 2020 compared with 1980 to 1990,and the existence of anticyclonic circulation over the Mongolian region resulted in significant easterly anomalies over the Qilian Mountains.There is a significant correlation between the MB of LHG12and the teleconnections.The summer MB is negatively correlated with the East Atlantic Model（EA）and positively correlated with the East Pacific/North Pacific Oscillation（EP/NP）and the Pacific Decadal Oscillation（PDO）.These teleconnections are also significantly correlated with summer temperature.There is a significant positive correlation between the Western Pacific model（WP）and winter mass balance.