Glacier Fluctuations between 1975 and 2008 in the Greater Himalaya Range of Zanskar,Southern Ladakh

Glaciers in the Himalaya are often heavily covered with supraglacial debris,making them difficult to study with remotely-sensed imagery alone.Various methods such as band ratios can be used effectively to map clean-ice glaciers;however,a thicker layer of debris often makes it impossible to distinguish between supraglacial debris and the surrounding terrain.Previously,a morphometric mapping approach employing an ASTER-derived digital elevation model has been used to map glaciers in the Khumbu Himal and the Tien Shan.This study on glaciers in the Greater Himalaya Range in Zanskar,southern Ladakh,aims (i) to use the morphometric approach to map large debris-covered glaciers;and (ii) to use Landsat and ASTER data and GPS and field measurements to document glacier change over the past four decades.Field work was carried out in the summers of 2008.For clean ice,band ratios from the ASTER dataset were used to distinguish glacial features.For debris-covered glaciers,topographic features such as slope were combined with thermal imagery and supervised classifiers to map glacial margins.The method is promising for large glaciers,although problems occurred in the distal and lateral parts and in the fore field of the glaciers.A multi-temporal analysis of glaciers in Zanskar showed that in general they have receded since at least the mid-to late-1970s.However,some few glaciers that advanced or oscillated - probably because of specific local environmental conditions - do exist.

冬季积累导致高亚洲冰川物质平衡空间差异

高亚洲山地冰川变化影响着周边数亿人的水源供给.以往研究表明,高亚洲各个地区冰川物质平衡存在较大的空间差异,但这种差异的原因尚不明确.本文提出了一种基于雷达卫星冰川积雪观测的新指数,以区分高亚洲地区冬季积累型和夏季积累型冰川.结合物质平衡数据进一步研究发现,夏季积累型冰川消融速度是冬季积累型冰川的4倍(2000~2018年间消融速度分别为-0.43±0.12 m w.e/a和-0.10±0.06 m w.e/a).研究结果表明了季节性积累对冰川物质平衡的重要性,强调了准确的降水观测对该地区未来冰川变化估算至关重要.

Potentially dangerous glacial lakes across the Tibetan Plateau revealed using a large-scale automated assessment approach

Glacial lake outburst floods(GLOFs) are a major concern in the Himalaya and on the Tibetan Plateau(TP),where several disasters occurring over the past century have caused significant loss of life and damage to infrastructure. This study responds directly to the needs of local authorities to provide guidance on the most dangerous glacial lakes across TP where local monitoring and other risk reduction strategies can subsequently be targeted. Specifically, the study aims to establish a first comprehensive prioritisation ranking of lake danger for TP, considering both the likelihood and possible magnitude of any outburst event(hazard), and the exposure of downstream communities. A composite inventory of 1,291 glacial lakes(>0.1 km^2) was derived from recent remote sensing studies, and a fully automated and object assessment scheme was implemented using customised GIS tools. Based on four core determinates of GLOF hazard(lake size, watershed area, topographic potential for ice/rock avalanching, and dam steepness), the scheme accurately distinguishes the high to very high hazard level of 19 out of 20 lakes that have previously generated GLOFs. Notably, 16% of all glacial lakes threaten human settlements, with a hotspot of GLOF danger identified in the central Himalayan counties of Jilong, Nyalam, and Dingri, where the potential trans-boundary threat to communities located downstream in Nepal is also recognised. The results provide an important and object scientific basis for decision-making, and the methodological approach is ideally suited for replication across other mountainous regions where such first-order studies are lacking.

The presence and influence of glacier surging around the Geladandong ice caps,North East Tibetan Plateau

Many glaciers and ice caps on the Tibetan Plateau have retreated and lost mass in recent years in response to temperature increases,providing clear evidence of the impact of climate change on the region.There is increasing evidence that many of the glaciers on the Tibetan Plateau have also shown periodically dynamic behaviour in the form of glacier surging and some even catastrophic collapse events.In this study,we examine the prevalence of glacier surging at the Geladandong ice caps,North East Tibetan Plateau,to better understand the role of surge events in the evolution of glacier mass loss budgets.Using glacier surface elevation change data over the period 1969—2018 and glacier surface velocity data from the ITS_LIVE dataset,we find that 19 outlet glaciers of the ice caps are of surge-type.Our multi-temporal measurements of glacier mass balance show that surge-type glacier mass budgets vary depending on the portion of the surge-cycle captured by geodetic data.At the regional level,pre-and post-surge glacier mass loss variability does not bias regional mass budget estimates,but enhanced,or suppressed,mass loss estimates are likely when small groups of glaciers are examined.Our results emphasise the importance of accurate surge-type glacier inventories and the need to maximise geodetic data coverage over glacierised regions known to contain surge-type glaciers.