Glacier Variations In The Yarlung Zangbo River Basin In China From 2000 To 2016

In recent years,global temperature increasing is the main reason for the accelerated melting of glaciers.The Qinghai-Tibet plateau,called the third pole of the world,has the densest glaciers except for the Antarctic and Arctic,which are significantly affected by climate change.Meanwhile,as one of the main rivers in the Qinghai-Tibet plateau,the Yarlung Zangbo River,which has an enormous scale of glaciers among the outflow rivers,is the leading distribution area of maritime glaciers.Glacier changes in the Yarlung Zangbo river basin have a tremendous impact on the water resources supply,ecological environment balance,prevent disasters,and economic development in South Asia.However,due to the limitation of the natural environment,data,and so on,the existing glacier inventories have some problems,such as large acquisition time span,incomplete glacier inventory,uncertain interpretation standards,making the study of glacier change based on these inventories has significant deviations and disputes.To sum up,the study on glacier inventory and recent glacier changes in the Yarlung Zangbo river basin has practical and scientific significance.In this paper,172 Landsat TM/ETM+/OLI images were used to determine glacier boundaries in the Yarlung Zangbo river basin in China in 2000,2016 and some regions with concentrated glaciers in 2020 by manual delineation and reference to high-precision Google Earth images and decorrelation images in SAR interferomentry.Changing characteristics of glacier area in the Yarlung Zangbo river basin during 2000-2016 and in specific study areas during the 1960s-2000 were analyzed.Based on SRTM DEM and Tan DEM,surface elevation and mass changes of glaciers during 2000-2014 were estimated by geodetic methods.Besides,observation data and the product of 37 meteorological stations were used to analyze the variation of temperature and precipitation in the Yarlung Zangbo river basin from 1981 to 2016,and the response of glaciers to climate change was discussed.The main conclusions are as follows:(1)In 2016,there were 11961 glaciers in the Yarlung Zangbo river basin,with a total area of8792.21±375.83 km².There were 6946 maritime glaciers covering an area of 5521.98 km²,and5015 continental glaciers covering an area of 3270.23 km².Due to different climates and topography,there were significant spatial differences in the distribution of glaciers in the basin.Affected by warm moist flow from the Bay of Bengal and uplifted topography of the Yarlung Zangbo Grand Canyon,there were more glaciers on the southern slope of mountains around the Yarlung Zangbo river basin than on the northern slope.Furthermore,glacier development near the Yarlung Zangbo Grand Canyon was more significant than in other areas.Among sub-basins,the Yiong Tsangpo river basin had the most significant number and area of glaciers,accounting for 29.79%and 33.56%of the total basin,respectively.From 2000 to 2016,the study area's glacier area decreased by 907.15±243.64 km²,accounting for 9.35±2.51%of the total glacier area in 2000,the rate of area change was-0.58±0.16%a^-1.The area shrinkage of maritime glaciers and continental glaciers accounted for 63.56%and 36.44%of glaciers'total area shrinkage.Results showed that the glaciers have been shrinking since 2000 in the Yarlung Zangbo river basin.The reduction of glacier area decreased with increasing area class and elevation,and glaciers in the northeast have lost the most area.In terms of spatial distribution,the shrinking rate of glacier area in the north bank of the Yarlung Zangbo river faster than that in the south bank,and west of the basin was faster than that the east.The monitoring results of some regions with concentrated glaciers showed that the basin's glaciers had an accelerated shrinking trend since the 1960s.(2)Glaciers in the Yarlung Zangbo river basin from 2000 to 2014 went into a state of mass loss,the decreasing rate of glacier surface elevation was 0.79±0.32 m a^-1,and the mass balance was-0.62±0.28 m w.e.a^-1.The thinning rates of the surface elevation of maritime glaciers and continental glaciers were 0.87±0.33 m a^-1 and 0.73±0.0.32 m a^-1.The surface elevation of the glacier in the low-altitude area decreased faster than that in the high-altitude area,and the maximum value was 1.42 m a^-1 in the elevation range of 4000-4200 m.There were accelerations of glacier surface elevation change from east to west across the basin,except for the Lohit river basin,in which the surface elevation decreased at a rate of 1.04±0.36 m a^-1.(3)Since 1981,the Yarlung Zangbo river basin's temperature increased rapidly,precipitation increased slowly before 1998 and decreased.The change of temperature and precipitation affected glacier shrinkage and mass loss in the study area.Because of the rising temperature,while the precipitation change had significant variability and uncertainty,the rising temperature was the dominant factor in glacier change.Overall,the rate of temperature increase on the north bank of the Yarlung Zangbo river was higher than that on the south bank,the western part was higher than the eastern section,and the low-altitude area was higher than the high-altitude area.Therefore,the area and mass loss were more significant in the western part of the study area and the low-altitude area.However,the smaller mass loss of glaciers in some regions was related to the small scale and high elevation of glaciers.