| China is the country with the most developed mountain glaciers in the world’s low to middle latitudes.Glaciers and their changes have important impacts on regional water resources security and human production and life.In the context of global warming,glacier in western China has been retreating and shows on an accelerating trend,which has attracted widespread attention from the academic community and local governments.Debris-covered glaciers refer to glaciers that are partially or completely covered by a layer of debris of varying thickness in the ablation zone.The material energy balance and response characteristics of such glaciers to climate change are complex due to differences in surface albedo.Based on Landsat remote sensing images and DEM data,this paper uses the TDSI(Temperature NDDI Slope Ice)method to extract the boundary of debris-covered glaciers(debris coverage >5%)in western China,analyzing the changes in the area of these glaciers and their debris cover from 2000 to 2022.The energy balance model was also used to simulate the mass balance of three typical debris-covered glaciers,Tomur,Rongbuk,and Yalong,and to analyze the spatial and temporal changes in the mass balance and energy budget of continental and maritime debris-covered glaciers.The main conclusions of this study are shown as follows:(1)A total of 384 debris-covered glaciers were extracted based on the TDSI method,accounting for 0.79% and 15.52% of the total number and area of glaciers in China.The extraction accuracy of the boundary of debris-covered glacier was 95.23%,among which 96.47% and 95.02% for continental and maritime debris-covered glaciers respectively;the accuracy of debris boundary was 92.20%,and 95.28% and 90.64% for continental and maritime glaciers respectively.(2)From 2000 to 2022,the overall trend of debris-covered glaciers is slightly retreating(-1.90%),but the proportion of debris area is increasing(16.41%).The area of maritime debris-covered glacier and clean ice both retreat more than that of continental ones,but the area of debris increases more significantly,and the area of debris below3200 m above sea level reaches 100%,and showed an obvious tendency of expanding to the upper part of glaciers,and the proportion of debris above the median elevation increases by 1.87%.Debris-covered glaciers are mainly located in the Tian Shan,Nyainqêntanglha,Himalayas and Karakorum Mountains,among which the Tian Shan and Karakorum glaciers are continental type,with small retreat of glacier area and slow increase of debris-covered area;while the Nyainqêntanglha Mountains are all maritime type,and some glaciers develop proglacial lakes near glacier terminus,resulting in accelerated retreat of glacier end and more significant increase of debris-covered area.Most of the Himalayas are continental glaciers(59)and only 17 are maritime glaciers,resulting in the rate of change of glaciers and debris areas is lower than that of Nyainqêntanglha Mountains.(3)The established energy and mass balance model can effectively describe the mass budget processes of glaciers,which is mainly reflected: the interannual variation of the simulated energy terms are highly correlated with the ERA5 reanalysis data;the mass balance obtained by simulation is consistent with that derived from other studies.Glacier mass balance is the most sensitive to temperature,when temperature rises by1℃,the mass balance changes by by-20 to-15%.The correlation with precipitation is lower than that of the average summer temperature,and the glacier mass balance changes under the influence of temperature in the absence of dramatic changes in precipitation.(4)All three simulated glaciers are characterised by a mass loss.The mass balance of Tomur Glacier is-0.34 m w.e./a,the mass balance of the clean ice is-0.21 m w.e./a and the debris-covered area is-0.13 m w.e./a,with the influence of the debris on the mass balance amounting to 38%.The mass balance of the Rongbuk Glacier is-0.75 m w.e./a,the mass balance of the clean ice is-0.36 m w.e./a and debris-covered area is-0.39 m w.e./a.The mass loss of the Yanong Glacier is more serious,with a mass balance of-1.05 m w.e./a,the mass balance of the clean ice area is-0.68 m w.e./a and the debris-covered area is-0.37 m w.e./a.Above the equilibrium line,glacier obtains the heat from the atmosphere through the turbulent heat exchange process to keep energy conservation,sublimation is the only way for mass loss.Below the equilibrium line,most of the net radiation income is used for heat transfer from the surface debris layer,weakening the latent heat of ablation of the ice surface,and the mass balance is influenced by the thickness distribution of the debris.(5)There are significant differences in the degree of mass balance loss between continental and maritime glaciers,with greater glacier mass loss as oceanicity becomes stronger,and less mass loss as continentality becomes stronger.The differences in glacier mass balance are determined by the differences in hydrothermal environment changes of different glaciers,which are mainly influenced by atmospheric circulation and climate change,and are independent of glacier type.The melting of debris-covered glaciers in the debris-covered area is mainly affected by the thickness and spatial distribution of the debris cover.Thin debris layers promote the melting of the underlying ice,while thick debris layers inhibit it.The uneven distribution of debris thickness leads to the extensive development of ice cliffs and glacial lakes in the debris area,which in turn affects the mass balance response characteristics of glaciers.The influence of debris thickness varies significantly between regions and types of debris-covered glacier areas,with debris playing a suppressive role in the ablation of continental glaciers,while contributing to accelerated ablation of maritime glaciers,especially the development and expansion of proglacial lakes near some glacier in the Qinghai-Tibet Plateau,further accelerating glacier retreat and mass loss. |
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