Change Of Glacier Volume Based On Multi-source Digital Elevation Model Over The Qilian Mountain During The Last 50 Years

The glaciers in the Qinghai-Tibet Plateau region have shown different degrees of melting in recent decades under the influence of continuous global warming.The Qilian Mountains are essential area for glacier change research in China,which are located in the northeastern part of the Qinghai-Tibet Plateau.Despite many studies from scholars at home and abroad reporting the glacier changes in some areas of Qilian Mountains,which are the key areas of the research on the glacier changes in China,volume changes of the large-scale glacier over multiple decades have not been well reconstructed,especially before the 21st century.Therefore,it is of great theoretical and practical significance to quantitatively estimate the glacier volume change of the entire Qilian Mountains in recent 50 years.Here,glacier volume change over the whole Qilian Mountains are quantified using Landsat ETM+/OLI and digital elevation models recon-structed from topographic maps,SRTM X-band radar data and sub-meter stereo imagery(Digital Globe World View-1/2/3 and Geo Eye-1).The main conclusions of the research are as follows:(1)Spatial and temporal variation of overall glacier surface elevation over the Qilian Mountains:Glaciers over the Qilian Mountains experienced significant surface lowering during the past 50 years.The glacier surface elevation lowering rate over the Qilian Mountains was 0.21±0.15 m a^-1from 1970 to 2000;and the mean glacier surface elevation lowering rate from 2000 to 2016 was estimated to be 0.56±0.21 m a^–1,which was twice than that from 1970to 2000.The glacier surface elevation over the all regions of the Qilian Mountains has been experienced significant lowering in the past 50 years.The space distinction of the glacier surface elevation over the all regions of the Qilian Mountains showed that the surface elevation lowering rate gradually increased from the west to east from 1970 to 2000,and the glacier surface elevation lowering rate was 0.70±0.27 m a^–1in the eastern Qilian Mountains,which was larger than western part(0.63±0.24 m a^–1)and middle part(0.47±0.19 m a^–1)during 2000 to 2016.In addition,the altitudinal distribution of rates of glacier elevation changes in 100 m elevation bins show that the glacier surface surface lowering rate decreases with increased elevation especially in the regions at 4500–5400 m altitudes.While in the regions below 4500 m and above 5400 m altitudes the relationship between the glacier surface elevation change and altitude is complicated;(2)Spatial and temporal variation of typical glacier surface elevation:In order to further explore the local differences of glacier surface elevation change over the Qilian Mountains,three typical glaciers of the Qilian Mountains were selected to research their glacier changes.The mean glacier surface elevation decrease rates of the Dunde glacier over the west part?Shulenan Mountain glacier over the middle part and Lenglongling glacier over the east part were estimated to be 0.16±0.12 m a^–1?0.15±0.12 m a^–1and 0.44±0.25 m a^–1,respectively,during 1970 to 2000.The mean glacier surface elevation decrease rate of them from 2000 to2016 were significant larger than that from 1970 to 2000,which were 0.43±0.26 m a^–1?0.37±0.25 m a^–1 and 0.70±0.47 m a^–1,respectively.Judging from space,the mean glacier surface elevation decrease rate of Shulenan Mountain was slightly smaller to that of Dunde glacier which were both much lower than that of Lenglongling glacier,over 1970–2000 and2000–2016;(3)The spatial and temporal variation of glacier volume in the overall Qilian Mountains:Glaciers over the Qilian Mountains experienced a continuous volume lossing during the past50 years.The glacier volume lossing rate over the Qilian Mountains from 1970 to 2000 was0.18±0.15 m w.e.a^–1,and the glacier volume lossing rate from 2000 to 2016 was estimated to be 0.48±0.18 m w.e.a^–1,which reveals accelerated glacier melting from 2000.The glacier volume over the all regions of the Qilian Mountains has been experienced significant lossing in the past 50 years.The space distinction of the glacier volume lossing over the all regions of the Qilian Mountains showed that the glacier volume lossing rate gradually increased from the west to east from 1970 to 2000,and the glacier volume lossing rate was 0.60±0.31 m w.e.a^–1 in the eastern Qilian Mountains,which was larger than western part(0.54±0.25 m w.e.a^–1)and middle part(0.40±0.21 m w.e.a^–1)during 2000 to 2016;(4)Spatial and temporal variability of typical glacier volume:In order to further explore the local differences of glacier volume change over the Qilian Mountains,three typical glaciers of the Qilian Mountains from the west to east part were selected to research their volume changes.The mean glacier volume lossing rates of the Dunde glacier over the west part?Shulenan Mountain glacier over the middle part and Lenglongling glacier over the east part were estimated to be 0.14±0.12 m w.e.a^–1?0.12±0.14 m w.e.a^–1and 0.37±0.31 m w.e.a^–1,during1970 to 2000.And the glacier volume lossing rates from 2000 to 2016 were significant larger than that from 1970 to 2000,which were 0.37±0.14 m w.e.a^–1?0.32±0.14 m w.e.a^–1 and0.60±0.26 m w.e.a^–1.Judging from space,the glacier volume lossing rate of Shulenan Mountain glacier was slightly smaller to that of Dunde glacier which were both much lower than that of Lenglongling glacier,over 1970–2000 and 2000–2016.