Zhangmu and Gyirong ports under the threat of glacial lake outburst flood

The Himalayas are prone to glacial lake outburst floods,which can pose a severe threat to downstream villages and infrastructure.The Zhangmu and Gyirong land treaty ports are located on the China-Nepal border in the central Himalayas.In recent years,the expansion of glacial lakes has increased the threat of these two port regions.This article describes the results of mapping the glacial lakes larger than 0.01 km^2 in the Zhangmu and Gyirong port regions and analyzes their change.It provides a comprehensive assessment of potentially dangerous glacial lakes and predicts the development of future glacial lakes.From 1988 to 2019,the glacial lakes in these port regions underwent"expansion",and moraine-dammed lakes show the most significant expansion trend.A total of eleven potentially dangerous glacial lakes are identified based on the assessment criteria and historical outburst events;most expanded by more than 150%from 1988 to 2019,with some by over 500%.The Cirenmaco,a moraine-dammed lake,is extremely prone to overtopping due to ice avalanches or the melting of dead ice in the dam.For other large lakes,such as the Jialongco,Gangxico and Galongco,ice avalanches may likely cause the lakes to burst besides self-destructive failure.The potential dangers of the Youmojianco glacial lakes,including lakes Nos.9,10 and 11,will increase in the future.In addition,the glacier-bed topography model predicts that 113 glacial lakes with a size larger than 0.01 km^2,a total area of 11.88 km2 and a total volume of 6.37×10^9 m^3 will form in the study area by the end of the 21 century.Due to global warming,the glacial lakes in the Zhangmu and Gyirong port regions will continue to grow in the short term,and hence the risk of glacial lake outburst floods will increase.

Long-term records of glacier evolution and associated proglacial lakes on the Tibetan Plateau(1976‒2020)

The glaciers on the Tibetan Plateau(TP)constitute critical sources of water for the proglacial lakes and many rivers found downstream.To better understand the evolution of glaciers and the impact of this on proglacial lakes,seven glaciers corresponding to continenṅtal,sub-continental,and marine climate types that are influenced by wester-lies and the Indian summer monsoon were selected for study.The evolution of the edges of these glaciers and their associated progla-cial lakes were identified based on the visual interpretation of Landsat TM/ETM+/OLI images.A dataset covering the period 1976-2020 that included the glacier and proglacial lake edge vectors was then created.The relative errors in the areas of the individual glaciers were less than 3%,and for the proglacial lakes these errors were in the range 0%-7%.The dataset was used to effectively compare the changes in glaciers and proglacial lakes that have occurred over the past four decades.The most striking changes that were found were the retreat of glaciers and the formation of small proglacial lakes.This dataset could also be used as a proxy to support research on changes in mountain glaciers,particularly their response to climate change and water resources.This response is of great scientific significance and is important in many applications,including assessments of the ecological problems caused by melting glaciers.The dataset can be downloaded from http://doi.org/10.57760/sciencedb.j00076.00131.

An approach to extracting surface supply relationships between glaciers and lakes on the Tibetan Plateau

Surface supply relationships between glaciers and lakes are needed to analyze and understand hydrological processes at regional and global scales.However,these supply relationships still cannot be extracted efficiently by existing methods.This paper proposes an automatic and efficient approach to extracting surface supply relationships between glaciers and lakes based on meltwater flow paths.The approach includes two stages:(1)identifying direct connections between objects(i.e.glaciers and lakes)based on flow direction derived from digital terrain analysis on a gridded digital elevation model(DEM)and(2)deriving all(or user-specified)kinds of surface supply relationships based on graph search.All computation-intensive steps in this approach have been parallelized;and all steps in the proposed approach have been integrated as an automatic program.Results for the Tibetan Plateau show that given outline data for glaciers and lakes and the Shuttle Radar Topography Mission DEM,the proposed approach can automatically derive diverse surface supply relationships under userspecified restrictions on the attributes of the supply route.The parallelization in the approach effectively improves the computing efficiency.The proposed approach could also be applied to developing a detailed fundamental dataset of supply relationships between glaciers and lakes for other region or period.

Distribution and transportation of mercury from glacier to lake in the Qiangyong Glacier Basin, southern Tibetan Plateau, China

The Tibetan Plateau is home to the largest aggregate of glaciers outside the Polar Regions and is a source of fresh water to 1.4 billion people. Yet little is known about the transportation and cycling of Hg in high-elevation glacier basins on Tibetan Plateau. In this study, surface snow,glacier melting stream water and lake water samples were collected from the Qiangyong Glacier Basin. The spatiotemporal distribution and transportation of Hg from glacier to lake were investigated. Significant diurnal variations of dissolved Hg（DHg） concentrations were observed in the river water, with low concentrations in the morning（8：00 am–14：00 pm） and high concentrations in the afternoon（16：00 pm–20：00 pm）. The DHg concentrations were exponentially correlated with runoff, which indicated that runoff was the dominant factor affecting DHg concentrations in the river water. Moreover, significant decreases of Hg were observed during transportation from glacier to lake. DHg adsorption onto particulates followed by the sedimentation of particulate-bound Hg（PHg） could be possible as an important Hg removal mechanism during the transportation process. Significant decreases in Hg concentrations were observed downstream of Xiao Qiangyong Lake, which indicated that the high-elevation lake system could significantly affect the distribution and transportation of Hg in the Qiangyong Glacier Basin.

Spatial and Temporal Dynamics of Lakes in Nam Co Basin, 1991–2011

Lakes in Tibet Plateau with little effects of human activities serve as important indicators of climate change. This study analysed remote sensing data and long term climate variables to examine the hydrological response of lakes in Nam Co Basin. The area changes of lakes were extracted by Landsat TM/ETM＋ and analysed by SRTM 3 DEM. And the ICESat elevation data between 2003 and 2009 were used to observe the lake level of the Nam Co Lake. The results show that the number of new formed glacier lakes increased by 36% and the area of glacier lakes increased by 36.7%（0.97 km^2） from 1991 to 2011. At the same time, the surface area of the Nam Co Lake expanded by 3.71%（72.64 km^2） of the original size in 1991, with a tendency value of 3.63 km^2 per year. The lake level of the Nam Co Lake shows an increase tendency of 0.24 m per year during 2003-2009. These variations appear to be related to an increase in mean annual temperature of 0.06 oC per year, and an increase in annual precipitation of 2.1 mm per year in summer in the last two decades. The increased number of lakes and increased area of glacial lakes reached a peak at an altitude of 5 500-5 600 m a.s.l.. The number of new formed glacier lakes and the area of glacier lakes tend to higher altitudes. Climate change has an important impact on the variation of the glacier lakes and the Nam Co Lake.