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.

Changes in the global cryosphere and their impacts:A review and new perspective

As one of the five components of Earth's climatic system,the cryosphere has been undergoing rapid shrinking due to global warming.Studies on the formation,evolution,distribution and dynamics of cryospheric components and their interactions with the human system are of increasing importance to society.In recent decades,the mass loss of glaciers,including the Greenland and Antarctic ice sheets,has accelerated.The extent of sea ice and snow cover has been shrinking,and permafrost has been degrading.The main sustainable development goals in cryospheric regions have been impacted.The shrinking of the cryosphere results in sea-level rise,which is currently affecting,or is soon expected to affect,17 coastal megacities and some small island countries.In East Asia,South Asia and North America,climate anomalies are closely related to the extent of Arctic sea ice and snow cover in the Northern Hemisphere.Increasing freshwater melting from the ice sheets and sea ice may be one reason for the slowdown in Atlantic meridional overturning circulation in the Arctic and Southern Oceans.The foundations of ports and infrastructure in the circum-Arctic permafrost regions suffer from the consequences of permafrost degradation.In high plateaus and mountainous regions,the cryosphere's shrinking has led to fluctuations in river runoff,caused water shortages and increased flooding risks in certain areas.These changes in cryospheric components have shown significant heterogeneity at different temporal and spatial scales.Our results suggest that the quantitative evaluation of future changes in the cryosphere still needs to be improved by enhancing existing observations and model simulations.Theoretical and methodological innovations are required to strengthen social economies'resilience to the impact of cryospheric change.

Manifestations and mechanisms of mountain glacier-related hazards

Mountain glacier-related hazards occur worldwide in response to increasing glacier instability and human activity intensity in modern glacierized regions.These hazards are characterized by their spatial aggregation and temporal repeatability.Comprehensive knowledge about mountain glacier-related hazards is critical for hazard assessment,mitigation,and prevention in the mountain cryosphere and downstream regions.This article systematically schematizes various mountain glacier-related hazards and analyzes their inherent associations with glacier changes.Besides,the processes,manifestations,and mechanisms of each of the glacier-related hazards are summarized.In the future,more extensive and detailed systematic surveys,for example,considering integrated ground−air−space patterns,should be undertaken for typical glacierized regions to enhance existing knowledge of such hazards.The use of coupled numerical models based on multisource data is challenging but will be essential to improve our understanding of the complex chain of processes involved in thermal−hydrogeomorphic glacier-related hazards in the mountain cryosphere.

Seasonal evolution of the englacial and subglacial drainage systems of a temperate glacier revealed by hydrological analysis

Englacial and subglacial drainage systems of temperate glaciers have a strong influence on glacier dynamics, glacier-induced floods, glacier-weathering processes, and runoff from glacierized drainage basins. Proglacial discharge is partly controlled by the geometry of the glacial drainage network and by the process of producing meltwater. The glacial-drainage system of some alpine glaciers has been characterized using a model based on proglacial discharge analysis. In this paper, we apply cross-correlation analysis to hourly hydro-climatic data collected from China＇s Hailuogou Glacier, a typical temperate glacier in Mt. Gongga, to study the seasonal status changes of the englacial and subglacial drainage systems by discharge-temperature （Q-T） time lag analy-sis. During early ablation season （April-May） of 2003, 2004 and 2005, the change of englacial and subglacial drainage system usually leads several outburst flood events, which are also substantiated by observing the leakage of supraglacial pond and cre-vasses pond water during field works in April, 2008. At the end of ablation season （October-December）, the glacial-drainage net-works become less hydro-efficient. Those events are evidenced by hourly hydro-process near the terminus of Hailuogou Glacier, and the analysis of Q-T time lags also can be a good indicator of those changes. However, more detailed observations or experi-ments, e.g. dye-tracing experiment and recording borehole water level variations, are necessary to describe the evolutionary status and processes of englacial and subglacial drainage systems evolution during ablation season.

Structural transformation of metal–organic framework with constructed tetravalent nickel sites for efficient water oxidation

A mixture of Ni and Fe oxides is among the most commonly active catalysts for the oxygen evolution reaction(OER)during the water oxidation process.In particular,Ni oxide incorporated with even a small amount of Fe leads to substantively enhanced OER activity.However,the critical role of Fe species during the electrocatalytic process is still under evaluation.Herein,we report nickel(oxy)hydroxide incorporated with Fe through the surface reconstruction of a bimetallic metal-organic framework(NiFe-MOF)during the water oxidation process.The spectroscopic investigations with theoretical calculations reveal the critical role of Fe in promoting the formation of highly oxidized Ni^(4+),which directly correlates with an enhanced OER activity.Both the geometric and electronic structu res of the as-reconstructed Ni_(1-x)Fe_(x)OOH electrocatalysts can be delicately tuned by the Ni-Fe ratio of the bimetallic NiFe-MOF,further affecting the catalytic activity.As a result,the Ni_(1-x)Fe_(x)OOH derived from Ni_(0.9)Fe_(0.1)-MOF delivers low overpotentials of 260 mV at 10 mA cm^(-2)and 400 mV at 300 mA cm^(-2).

MODIS observed snow cover variations in the Aksu River Basin, Northwest China

A major proportion of discharge in the Aksu River is contributed from snow-and glacier-melt water.It is therefore essential to understand the cryospheric dynamics in this area for water resource management.The MODIS MOD10A2 remotesensing database from March 2000 to December 2012 was selected to analyze snow cover changes.Snow cover varied significantly on a temporal and spatial scale for the basin.The difference of the maximum and minimum Snow Cover Fraction(SCF)in winter exceeded 70%.On average for annual cycle,the characteristic of SCF is that it reached the highest value of 53.2%in January and lowest value of 14.7%in July and the distributions of SCF along with elevation is an obvious difference between the range of 3,000 m below and 3,000 m above.The fluctuation of annual average snow cover is strong which shows that the spring snow cover was on the trend of increasing because of decreasing temperatures for the period of 2000-2012.However,temperature in April increased significantly which lead to more snowmelt and a decrease of snow cover.Thus,more attention is needed for flooding in this region due to strong melting of snow.

Moraine-dammed glacial lake changes during the recent 40 years in the Poiqu River Basin,Himalayas

Glacier retreat is not only a symbol of temperature and precipitation change, but a dominating factor of glacial lake changes in alpine regions, which are of wide concern for high risk of potential outburst floods. Of all types of glacial lakes, moraine-dammed lakes may be the most dangerous to local residents in mountain regions. Thus, we monitored the dy- namics of 12 moraine-dammed glacial lakes from 1974 to 2014 in the Poiqu River Basin of central west Himalayas, as well as their associated glaciers with a combination of remote sensing, topographic maps and digital elevation models （DEMs）. Our results indicate that all monitored moraine-dammed glacial lakes have expanded by 7.46 km2 in total while the glaciers retreated by a total of 15.29 km2 correspondingly. Meteorological analysis indicates a warming and drying trend in the Nyalam region from 1974 to 2014, which accelerated glacier retreat and then augmented the supply of moraine-dammed glacial lakes from glacier melt. Lake volume and water depth changed from 1974 to 2014 which indicates that lakes Kangxico, Galongco, and Youmojanco have a high potential for outburst floods and in urgent need for continuous moni- toring or artificial excavation to release water due to the quick increase in water depths and storage capacities. Lakes Jialongco and Cirenmaco, with outburst floods in 1981 and 2002, have a high potential risk for outburst floods because of rapid lake growth and steep slope gradients surrounding them.

Editorial for the special issue in memoriam to Prof.Xie Zichu

Prof.Xie Zichu passed away on January 25,2020 in Changsha,Hunan Province,China at the age of 83 years old.Being one of the internationally renowned and highly respected glaciologists of China,this issue is dedicated with all respect in memory of him for his life-long effort and contribution to advance studies on glaciology in China.He has undertaken field investigations on glacier mass balance.

Englacial hydrological characteristics of a typical continental-type glacier in China as detected by ground-penetrating radar

The englacial structures and ice thickness of the Laohugou No. 12 （L12） Glacier in the Qilian Mountains, China, were retrieved from ground-penetrating radar （GPR） profile dzta acquired in August of 2007. Here the interpretation of a typical GPR image is validated using two-dimensional, Finite-Difference Time-Domain （FDTD） numerical modeling. Data analyses revealed many en- glacial characteristics, such as temperate ice, crevasses, and cavities at the position of convergence between the eastern and west- ern glacial branches of L12, and at an altitude between 4,600 and 4,750 m a.s.1, on the east branch. Combining ice thickness, en- glacial structures, subglacial topography, and surface flow velocities of this glacier, we analyzed the reasons for the distribution of temperate ice. The results show that greater englacial water content is associated with englacial crevassing and surface moulins, which allow water to be channeled to the temperate ice aquifer beneath the surface cold ice layer. Analysis of air temperature data shows that as more meltwater imports into the ice body, this has a great effect on water conservation and dynamics conditions. With climate warming, and under the influence of crevasses, subglacial structures, and ice thickness, ice thickness reduction on the L12 east branch is more rapid than that on the west branch.

青藏高原及周边石冰川识别、冰储量及动力学过程研究进展

青藏高原及周边分布着数量众多的石冰川,因其独特的蓄水功能和气候响应特征,不仅影响区域潜在的固态水资源,还增加了相应灾害发生的风险,受到越来越多的关注。当前,对石冰川识别、冰储量估算及其动力学过程模拟的探讨还较为缺乏,导致无法准确评估广大无资料或缺资料地区的石冰川变化及其气候响应特征。在系统梳理青藏高原及周边石冰川分布特征的基础上,综合回顾和总结了石冰川识别方法、冰储量估算方法、动力学过程及其模拟的研究进展。受观测数据缺乏和方法不确定性等问题的限制,当前青藏高原及周边石冰川编目、识别和冰储量估算精度仍面临诸多挑战。展望未来,应深入认识气候—石冰川动力学过程的相互作用机制,强化天—空—地多层次、多角度和多手段的石冰川监测,集成人工智能和新观测技术的石冰川识别和冰储量估算方法,准确评估气候变化条件下青藏高原及周边石冰川变化、未来趋势及其影响,进而服务于青藏高原及周边区域社会经济可持续发展。

青藏高原及周边地区近期冰川状态失常与灾变风险

青藏高原及周边地区是除南、北极地区之外全球最重要的冰川资源富集地.近百年来,青藏高原及周边地区冰川整体处于缓慢退缩状态,但20世纪90年代以来,这种状态发生了根本变化.以东帕米尔-喀喇昆仑-西昆仑地区冰川相对稳定甚至部分冰川前进为特征的'喀喇昆仑异常'是青藏高原及周边地区冰川状态失常的一种表现形式;而青藏高原东南地区冰川加速退缩则是这一地区冰川失常的另一种表现形式.高海拔地区的异常升温是青藏高原及周边地区冰川状态失常的重要驱动力.另外,这种冰川状态失常还与气候变暖背景下的西风和季风大气环流过程有关.随着全球变暖的加剧,冰川状态失常直接导致冰崩、冰湖溃决等灾变风险的增加.应对青藏高原及周边地区冰川状态失常的不利影响,需要进一步加强冰川变化监测与研究,加大冰川灾害防范力度.

Monitoring thickness and volume changes of the Dongkemadi Ice Field on the Qinghai-Tibetan Plateau (1969-2000) using Shuttle Radar Topography Mission and map data

This paper presents the first measurement of multi-decadal thickness and volume changes(1969?2000)of the Dongkemadi Ice Field(DIF)in the Tanggula Mountains,central Qinghai-Tibetan Plateau,China,using multi-source remote sensing data.These include the Shuttle Radar Topography Mission(SRTM)Digital Elevation Model(DEM)acquired in February,2000,a DEM generated by digitising analogue topographic maps from 1969,and Landsat ETM?imagery from 2000.Digital glacier outlines and GIS-based processing were used to calculate an elevation difference map to evaluate the relative elevation error of these two DEMs over ice-free areas.This methodwas also used to identify regions of glacier elevation thinning and thickening corresponding to glacier mass loss and gain.Analysis of 67,520 points on flat grass and rock terrain surrounding the DIF,with a slope less than 258,showed a mean elevation difference of?0.90 m and a standard deviation of 5.58 m.A thickness change error within 96 m was estimated.Between 1969 and 2000,76.51%of the whole DIF area appeared to be thinning while 23.49%showed thickening.The average glacier surface thinning was?12.58 m with a standard deviation of 18.29 m and the estimated volume loss was 1.17 km 3.The standard deviation of volume change was 0.0006 km 3 over the DIF.A thinning rate up to 0.4190.194 m a?1 or 0.038 km 3 a?1 for the volume loss was observed for the whole ice field,which seems to be evidence for the ongoing retreat of glaciers on the Qinghai-Tibetan Plateau.It was found that the spatial thickness change pattern derived from the remote sensing method was consistent with the thickness change results of the Small Dongkemadi Glacier(SDG)from field measurements.The estimated error of the annual thickness change rate was on the order of 5%.The relationship between elevation change and absolute glacier elevation over typical glaciers was also analysed,showing considerable variability.These changes have possibly resulted from increased temperature and decreased precipitation in this region.