An integrated deep learning and object-based image analysis approach for mapping debris- covered glaciers

Evaluating glacial change and the subsequent water stores in high mountains is becoming increasingly necessary, and in order to do this, models need reliable and consistent glacier data. These often come from global inventories, usually constructed from multi-temporal satellite imagery. However, there are limitations to these datasets. While clean ice can be mapped relatively easily using spectral band ratios, mapping debris-covered ice is more difficult due to the spectral similarity of supraglacial debris to the surrounding terrain. Therefore, analysts often employ manual delineation, a time-consuming and subjective approach to map debris-covered ice extents. Given the increasing prevalence of supraglacial debris in high mountain regions, such as High Mountain Asia, a systematic, objective approach is needed. The current study presents an approach for mapping debris-covered glaciers that integrates a convolutional neural network and object-based image analysis into one seamless classification workflow, applied to freely available and globally applicable Sentinel-2 multispectral, Landsat-8 thermal, Sentinel-1 interferometric coherence, and geomorphometric datasets. The approach is applied to three different domains in the Central Himalayan and the Karakoram ranges of High Mountain Asia that exhibit varying climatic regimes, topographies and debris-covered glacier characteristics. We evaluate the performance of the approach by comparison with a manually delineated glacier inventory, achieving F-score classification accuracies of 89.2%–93.7%. We also tested the performance of this approach on declassified panchromatic 1970 Corona KH-4B satellite imagery in the Manaslu region of Nepal, yielding accuracies of up to 88.4%. We find our approach to be robust, transferable to other regions, and accurate over regional (>4,000 km2) scales. Integrating object-based image analysis with deep-learning within a single workflow overcomes shortcomings associated with convolutional neural network classifications and permits a more flexible and robust approach for mapping debris-covered glaciers. The novel automated processing of panchromatic historical imagery, such as Corona KH-4B, opens the possibility of exploiting a wealth of multi-temporal data to understand past glacier changes.publishedVersio

Reconstructing the Chongbaxia Tsho glacial lake outburst flood in the Eastern Himalaya: Evolution, process and impacts

Glacial lake outburst floods (GLOF) are one of the most destructive natural disasters. Understanding GLOF evolution, and their impacts, plays a fundamental role in GLOF hazard assessment and risk management. Reconstructing historical GLOFs is an important exercise because detailed case studies of such glacial hazards are rare, which hinders the capacity of glacial hazard practitioners to learn from these events. In this study, we reconstruct a historical GLOF from moraine-dammed Chongbaxia Tsho (89.745°E, 28.211°N) in the Eastern Himalaya, which is a unique case study because the outburst flood cascaded into two further lakes downstream. We employ a combination of i) multi-source and multi-temporal satellite imagery, ii) field investigation (including an unmanned aerial vehicle survey), iii) numerical dam breach and hydrodynamic modelling and, iv) qualitative and quantitative cryospheric and meteorological analysis, to investigate the evolution of the GLOF hazard, simulate moraine dam failure and GLOF propagation, and explore the role that long- and short-term climate trends played in providing the conditioning factors for the outburst. Chongbaxia Tsho expanded rapidly between 1987 until 2001 in response to glacier recession most likely caused by a regional warming trend of +0.37 °C per decade. Based on satellite image analysis we refine the outburst date to be 6 August 2001, instead of 6 August 2000, as previously reported, and attribute an ice avalanche into the glacial lake originating from the receding parent glacier as the most likely trigger for moraine dam failure. Through DEM differencing and lake level decrease, we estimate that a total water volume of 27.1 ± 1.6 × 106 m3 was released from the lake during the event, and using dam breach modelling we estimate that the peak discharge at the breach was >6600 m3 s−1. The GLOF flowed through downstream Chongbamang Tsho and Chongbayong Tsho, both of which served to attenuate the GLOF and reduce downstream losses; the latter stored an estimated 96% of the flood volume. Precipitation totals in the weeks preceding the GLOF exceeded the historical mean by up to 40%, and may have contributed to instability of the parent glacier, and generation of an ice avalanche with enough impact energy to cause lake water to overtop the moraine dam and initiate breach development. A future GLOF from Chongbaxia Tsho cannot be ruled out, but more field data, including detailed lake bathymetry, and information pertaining to the sedimentological and geotechnical characteristics of the moraine dam, are required for a more robust parameterization of a predictive GLOF model and quantification of the hazard posed by a future GLOF

Glacier Change, Supraglacial Debris Expansion and Glacial Lake Evolution in the Gyirong River Basin, Central Himalayas, between 1988 and 2015

Himalayan glacier changes in the context of global climate change have attracted worldwide attention due to their profound cryo-hydrological ramifications. However, an integrated understanding of the debris-free and debris-covered glacier evolution and its interaction with glacial lake is still lacking. Using one case study in the Gyirong River Basin located in the central Himalayas, this paper applied archival Landsat imagery and an automated mapping method to understand how glaciers and glacial lakes interactively evolved between 1988 and 2015. Our analyses identified 467 glaciers in 1988, containing 435 debris-free and 32 debris-covered glaciers, with a total area of 614.09 ± 36.69 km2. These glaciers decreased by 16.45% in area from 1988 to 2015, with an accelerated retreat rate after 1994. Debris-free glaciers retreated faster than debris-covered glaciers. As a result of glacial downwasting, supraglacial debris coverage expanded upward by 17.79 km2 (24.44%). Concurrent with glacial retreat, glacial lakes increased in both number (+41) and area (+54.11%). Glacier-connected lakes likely accelerated the glacial retreat via thermal energy transmission and contributed to over 15% of the area loss in their connected glaciers. On the other hand, significant glacial retreats led to disconnections from their proglacial lakes, which appeared to stabilize the lake areas. Continuous expansions in the lakes connected with debris-covered glaciers, therefore, need additional attention due to their potential outbursts. In comparison with precipitation variation, temperature increase was the primary driver of such glacier and glacial lake changes. In addition, debris coverage, size, altitude, and connectivity with glacial lakes also affected the degree of glacial changes and resulted in the spatial heterogeneity of glacial wastage across the Gyirong River Basin

Remote Sensing of Surface Water Dynamics in the Context of Global Change - A Review

Inland surface water is often the most accessible freshwater source. As opposed to groundwater, surface water is replenished in a comparatively quick cycle, which makes this vital resource—if not overexploited—sustainable. From a global perspective, freshwater is plentiful. Still, depending on the region, surface water availability is severely limited. Additionally, climate change and human interventions act as large-scale drivers and cause dramatic changes in established surface water dynamics. Actions have to be taken to secure sustainable water availability and usage. This requires informed decision making based on reliable environmental data. Monitoring inland surface water dynamics is therefore more important than ever. Remote sensing is able to delineate surface water in a number of ways by using optical as well as active and passive microwave sensors. In this review, we look at the proceedings within this discipline by reviewing 233 scientific works. We provide an extensive overview of used sensors, the spatial and temporal resolution of studies, their thematic foci, and their spatial distribution. We observe that a wide array of available sensors and datasets, along with increasing computing capacities, have shaped the field over the last years. Multiple global analysis-ready products are available for investigating surface water area dynamics, but so far none offer high spatial and temporal resolution

Origin and evolution of proglacial lakes in the Patagonian Andes

Vznik a vývoj proglaciálních jezer v Patagonských Andách ABSTRAKT: Proglaciální jezera jsou dynamické vodní hmoty, které jsou zásadně ovlivněny vývojem ledovcových mas, morfologií reliéfu a klimatickými faktory. V současné době se ledovce vyznačují převážně postupným táním, které úzce souvisí s globálními změnami klimatu. S ústupem horského zalednění se zvětšuje objem vody ledovcových jezer, což může vést ke zvýšenému riziku přelití, či protržení hrází jezer. Cílem této práce bylo nejdříve formou rešerše popsat, jak tato jezera vznikají, jaké faktory hrají roli v jejich vývoji a jak ona samotná mohou ovlivňovat své okolí. Dále bylo na základě vytvořené inventarizační tabulky prostorově a časově analyzováno 640 jezer v oblasti Severopatagonského ledovcového pole v Patagonských Andách v časovém rozmezí od roku 1984 až po současnost. Výsledky potvrzují předpoklad, že spolu s úbytkem ledovcových hmot dochází v této oblasti také ke zvětšování a vzniku nových ledovcových jezer. Práce se snaží prokázat souvislost s klimatickými daty, ačkoliv ta jsou pro tento region poměrně nedostatečná. Klíčová slova: proglaciální jezera, ledovce, hrazení jezer, Severopatagonské ledovcové pole, GLOFOrigin and evolution of proglacial lakes in the Patagonian Andes ABSTRACT: Proglacial lakes are dynamic water bodies affected by the evolution of glacier ice masses, morphology and climatic factors. Mountain glaciers are very sensitive to climate change, which has caused their continuous recession recent decades. Glacier retreat is closely linked to an increase in the volume of proglacial lakes, especially in high mountain areas. The growth of proglacial lakes can also lead to increased probability of overtopping or dam rupture, also known as GLOF. The first aims of the presented thesis are to describe how proglacial lakes are formed, what factors can influence their continuous evolution and, lastly, how the lakes can affect their surroundings. In order to perform the spatial and temporary analysis, an inventory of the proglacial lakes in the North Patagonian Icefield was made, as this area has not yet been properly studied. In the time scale from 1984 till now, 640 lakes were characterised. The results show that along with glacier retreat, proglacial lakes are increasing in both size and number. However, the correlation with the climatic data is limited because of its poor quality and inadequate distribution in this area. Keywords: glacial lakes, glaciers, lake-dams, North Patagonian Icefield, GLOFKatedra fyzické geografie a geoekologieDepartment of Physical Geography and GeoecologyFaculty of SciencePřírodovědecká fakult

Explaining recent heterogeneous glacier change in the Annapurna Conservation Area, central Himalayas

PhD ThesisSince the 1970s, Himalayan glaciers have been shrinking in area, losing mass and decelerating in conjunction with warming air temperatures. This has serious implications for regional water resources. However, recent glacier change has been spatially heterogeneous and significant uncertainty remains about the sources (e.g. supraglacial debris, glacial hypsometry, avalanche-contributing area) of this local variability in the Himalayan glacier response to climate change. This thesis aims to characterise recent glacier changes in the Annapurna Conservation Area (ACA) in central Nepal and identify the extent and sources of local variability in the glacier change signal across a range of spatial (regional-, glacier- and sub-glacier-scale) and temporal (decadal to hourly) scales. Results show widespread glacier area loss (8.5% between 2000 and 2014/15) and mass loss (-0.28 ± 0.24 m w.e. a-1 between 2000 and 2013/16) in the ACA. However, glacier changes were spatially variable, with distinct glacier responses observed between sub-regions in the ACA. Individual glacier change was also modulated by supraglacial debris and glacier hypsometry. However, glacier elevation and avalanche-contributing area only influenced glacier change in the northern part of the study region, indicating that the strength of local controls was not spatially uniform. This thesis also identified another source of glacier response variability in the ACA, of potentially very localised importance, through the documentation of the first surge-type glacier in the central Himalayas. Sabche glacier had a very short surge cycle (~10 years), which is hypothesised to be modulated by subglacial topography, a mechanism that is rarely documented in published literature. Lastly, field data from Annapurna South glacier showed that the temperature and thermal properties of supraglacial debris varied both seasonally and between debris profiles of different thickness, which in turn had an important influence on the timing and magnitude of ablation. Overall, this thesis demonstrates the scale of local glacier change variability in the ACA and shows that the sources of this variability are complex and far from uniform. This work helps to put bounds on the level of noise occurring in the Himalayan glacier change signal and what can be considered a ‘normal’ range of variability. This heterogeneity should be taken into consideration when predicting how Himalayan glaciers will respond to climate change, and the impact of these glacier changes on local communitiesIAPETUS NERC Doctoral Training Partnershi