| High Mountains Asia(HMA)is the world’s largest modern glacier region in low and middle latitudes.It is also the water-source place of Yangtze River and Yellow River in China,as well as many international rivers in South Asia and Southeast Asia.The IPCC AR5 special report pointed out that HMA is getting warm over the recent decades at an average rate of 0.3℃ per decade,which is as twice as the rate of the global warming.Against this background,glaciers melting and mass lossing are intensifing in this area.This will not only raise the sea level,but will also have an impact on regional climate change,ecological environment,and water resource utilization.Therefore,the study of the mass balance of mountain glaciers has significant scientific research and civil application for global climate change,early warning of glacier disasters,and regional water resources utilization and management.Nowadays,the methods used to estimate the mass balance of mountain glaciers mainly include the glaciological method,hydrology method,gravimetric method,glacier surface parameters method and geodetic method.The geodetic method of using multi-period DEM data in a glacier area to obtain ice thickness changes and glacier mass balance within a certain period of time.In view of its simple principle,easy operation,and high spatial resolution of data,this method has become the main method for estimating the mass balance of glaciers.The mass balance estimation of large-scale glaciers in HMA is mainly based on ICESat altimetry,GRACE satellite gravity and high-precision DEM and other geodetic observation data.The uncertainty of the glacial mass balance results is large due to the low spatial resolution of GRACE satellite data and the strong influence of the land water storage on the gravity measurement results.In addition,the spatial sampling of ICESat laser altimetry data is sparse,which may lead to large deviations in the mass balance results.HMA regions still lack high-precision,large-scale glacier mass balance results,and there are certain differences in glacier mass balance results from different studies.In addition,when using radar-derived DEM to estimate the mass balance of glaciers,the problem of radar penetration depth needs to be solved urgently.In particular,the HMA region is located in complex and dangerous mountainous areas such as high steepness,high coldness and high ground stress.The spatial characteristics and regional differences of glacier mass balance changes are not clear and the causes are complex and diverse.Therefore,a more in-depth and systematic study of the large-scale HMA glacier mass balance is urgent needed.This study uses the synchronized SRTM X-band and C-band DEM data products to construct a altitude-related radar penetration difference model in HMA and improves the glacier mass balance estimation method based on SRTM DEM.This study also uses multi-source optical DEM and SRTM DEM to obtain the results of large-scale glacier thickness changes and mass balance in HMA during 2000-2014 Besides,this study analyzes the regional characteristics of the HMA glaciers’ mass balance and its relationship with local morphological factors and climate factors.The main research content and conclusions of the paper are summarized as follows:(1)Research on the linear relationship model between SRTM C/X band radar penetration depth difference and altitude.Based on the SRTM DEM product,this paper analyzes the elevation changes of C/X band DEM in the HMA ice area,and obtains the SRTM C/X band penetration difference in 92%glacier area(glacier area greater than 0.1 km2)of 1×10 grid,and found that the penetration difference has a strong linear correlation with the altitude.Based on the above results,a linear relationship model between the altitude and penetration depth difference of 15 glacier regions is established.Finally,the influence of the debris-covered area on the penetration depth difference and the possible reasons for penetration depth estimation errors are analyzed.The results demonstrate that in the HMA region,the C/X band penetration depth difference is between-1.67±0.65 m and 7.63±0.99 m,with an average value of 2.40±0.04 m,and the SRTM C/X band radar penetration depth difference has a strong linear correlation with the altitude.In addition,the penetration depth difference of the glacier debris-cover region presents a certain degree of randomness and has no linear relationship with the altitude.(2)Research on mass balance estimation in HMA areas.Based on multi-source optical data DEM and SR.TM DEM,this paper obtaines the results of elevation change rate of HMA glaciers from 2000 to 2014 and the mass balance results of more than 28000 glaciers(with an area of more than 0.1km2),and the characteristics and trends of the two changes are analyzed.Finally,taking Laohugou glacier 12 as an example,using DEM data from 2000/2013/2014/2015,the results of glaciers mass balance in multiple periods have been obtained.The results show that the average mass balance of HMA glaciers is-0.13 m w.e./yr,indicating that the whole HMA glaciers are in a state of ablation.The Laohugou No.12 Glacier was in the mass loss stage from 2000 to 2015,but the rate of ice thickness thinning decreased from 2013 to 2015,which was related to the increase in precipitation in 2015.(3)Research on influencing factors of glacier mass balance.Based on the obtained results of the glacier mass balance,this paper uses the correlation analysis method to obtain the relationship between the glacier mass balance and local morphological factors,glacier surface parameters and climate factors.The results show that:First,the median glacier elevation,glacial tongue elevation,glacial tongue slope,and average glacier slope are related to the mass balance of the glacier.Second,there is no linear relationship between glacier mass balance and glacier area,glacier velocity and percentage of debris cover.Third,part of the regional precipitation and mass balance are positively correlated,and temperature and mass balance are negatively correlated.Fourth,the linear relationship between the interdecadal mean glacier elevation change and the mean albedo only exists in some areas,such as the eastern Tianshan Mountains and the interior of the Qinghai-Tibet Plateau. |
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