scholarly journals Modeling Surface Processes on Debris-Covered Glaciers: A Review with Reference to the High Mountain Asia

Water ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 101
Author(s):  
Da Huo ◽  
Zhaohui Chi ◽  
Andong Ma
Keyword(s):  
Hydrological Cycle ◽  
Current Knowledge ◽  
Numerical Models ◽  
Mass Movement ◽  
Surface Processes ◽  
Coupled Processes ◽  
High Mountain ◽  
Glacier Surface ◽  
In Situ Data ◽  
Debris Transport

Surface processes on debris-covered glaciers are governed by a variety of controlling factors including climate, debris load, water bodies, and topography. Currently, we have not achieved a general consensus on the role of supraglacial processes in regulating climate–glacier sensitivity in High Mountain Asia, which is mainly due to a lack of an integrated understanding of glacier surface dynamics as a function of debris properties, mass movement, and ponding. Therefore, further investigations on supraglacial processes is needed in order to provide more accurate assessments of the hydrological cycle, water resources, and natural hazards in the region. Given the scarcity of long-term in situ data and the difficulty of conducting fieldwork on these glaciers, many numerical models have been developed by recent studies. This review summarizes our current knowledge of surface processes on debris-covered glaciers with an emphasis on the related modeling efforts. We present an integrated view on how numerical modeling provide insights into glacier surface ablation, supraglacial debris transport, morphological variation, pond dynamics, and ice-cliff evolution. We also highlight the remote sensing approaches that facilitate modeling, and discuss the limitations of existing models regarding their capabilities to address coupled processes on debris-covered glaciers and suggest research directions.

Evaluating Simplified Numerical Models of Debris-Covered Glaciers

2021 ◽  
Author(s):  
James C. Ferguson ◽  
Tobias Bolch ◽  
Andreas Vieli
Keyword(s):  
Numerical Models ◽  
Spatial Scales ◽  
Global Scale ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Wide Range ◽  
Debris Cover ◽  
Debris Transport ◽  
Modelling Studies

<p>The transient response of debris-covered glaciers to a changing climate is governed by nonlinear feedbacks between ice dynamics, debris transport, and glacier geometry and that act over a wide range of temporal and spatial scales. Current numerical models that are able to accurately represent the relevant physical processes are computationally expensive since they must track the debris transport not only at the glacier surface but also englacially. This makes such models difficult to use for simulations at the regional to global scale.</p><p>In order to address this challenge, we developed a fully coupled numerical model that solves both englacial debris transport and ice flow and includes the effect of debris cover on surface ablation. We use this model to evaluate different simplified approaches to modelling debris-covered glaciers. These simplifications include parametrized 1-D debris transport models, parametrized models of surface mass balance that include debris cover effects, and zero-dimensional models. We compare the model performances using a number of tests with an idealized synthetic glacier geometry and a range of forcings, thereby allowing for an evaluation of the relative merits of each approach. A key goal of this work is to provide guidance and tools for modelling studies involving debris cover at the regional to global scale.</p>

scholarly journals Numerical Simulation of Supraglacial Debris Mobility: Implications for Ablation and Landform Genesis

2021 ◽  
Vol 9 ◽  
Author(s):  
Peter L. Moore
Keyword(s):  
Conceptual Models ◽  
Slope Angle ◽  
Passive Movement ◽  
Coupled Processes ◽  
Glacier Surface ◽  
Ice Surface ◽  
Debris Transport ◽  
Hillslope Scale ◽  
Genesis Model ◽  
The Relationship

Supraglacial debris does not remain fixed atop ablating ice, but can move across the ice surface as supraglacial topography evolves. This active debris movement (distinct from passive movement due to underlying ice motion) affects landform genesis as well as the rate and spatial distribution of ablation. While observations of debris transport across evolving supraglacial topography are abundant, models of these coupled processes over timescales of decades and longer are few. Here I adapt a numerical model of coupled ablation and downslope debris transport to simulate the evolution of an idealized debris-covered glacier on the timescale of complete de-icing. The model includes ablation that depends on supraglacial debris thickness and a hillslope-scale debris transport function that scales non-linearly with slope angle. Ice thickness and debris distribution evolve with model time, allowing complete simulation of de-icing and landform construction in an idealized glacier test-section. The model produces supraglacial relief that leads to topographic inversions consistent with conceptual models of hummocky landform genesis. Model results indicate that the relief of the glacier surface and postglacial hummocks depend on the relationship between characteristic timescales for ablation and debris transport, which is defined as an index of debris mobility. When debris mobility is high, topographic inversions are rapid and supraglacial and postglacial relief are subdued. When debris mobility is low, more pronounced supraglacial relief is produced, but postglacial relief remains subdued. An intermediate mobility appears to optimize both postglacial relief and the rate of de-icingcompared with both highly-mobile and immobile debris. This enhancement of de-icing due to debris mobility could contribute to the observed anomalous rates of ablation in some debris-covered glaciers.

scholarly journals Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains

2015 ◽  
Vol 3 (3) ◽  
pp. 333-362 ◽  
Author(s):  
E. Pohl ◽  
M. Knoche ◽  
R. Gloaguen ◽  
C. Andermann ◽  
P. Krause
Keyword(s):  
Remote Sensing ◽  
Hydrological Cycle ◽  
Climatic Variability ◽  
Surface Processes ◽  
Glacier Mass Balance ◽  
Clear Understanding ◽  
Data Set ◽  
In Situ Data ◽  
Pamir Mountains

Abstract. A clear understanding of the hydrology is required to capture surface processes and potential inherent hazards in orogens. Complex climatic interactions control hydrological processes in high mountains that in their turn regulate the erosive forces shaping the relief. To unravel the hydrological cycle of a glaciated watershed (Gunt River) considered representative of the Pamir Mountains' hydrologic regime, we developed a remote-sensing-based approach. At the boundary between two distinct climatic zones dominated by the Westerlies and Indian summer monsoon, the Pamir Mountains are poorly instrumented and only a few in situ meteorological and hydrological data are available. We adapted a suitable conceptual distributed hydrological model (J2000g). Interpolations of the few available in situ data are inadequate due to strong, relief-induced, spatial heterogeneities. Instead of these we use raster data, preferably from remote sensing sources depending on availability and validation. We evaluate remote-sensing-based precipitation and temperature products. MODIS MOD11 surface temperatures show good agreement with in situ data, perform better than other products, and represent a good proxy for air temperatures. For precipitation we tested remote sensing products as well as the HAR10 climate model data and the interpolation-based APHRODITE data set. All products show substantial differences both in intensity and seasonal distribution with in situ data. Despite low resolutions, the data sets are able to sustain high model efficiencies (NSE ≥ 0.85). In contrast to neighbouring regions in the Himalayas or the Hindu Kush, discharge is dominantly the product of snow and glacier melt, and thus temperature is the essential controlling factor. Eighty percent of annual precipitation is provided as snow in winter and spring contrasting peak discharges during summer. Hence, precipitation and discharge are negatively correlated and display complex hysteresis effects that allow for the effect of interannual climatic variability on river flow to be inferred. We infer the existence of two subsurface reservoirs. The groundwater reservoir (providing 40 % of annual discharge) recharges in spring and summer and releases slowly during autumn and winter, when it provides the only source for river discharge. A not fully constrained shallow reservoir with very rapid retention times buffers meltwaters during spring and summer. The negative glacier mass balance (−0.6 m w.e. yr

scholarly journals Mapping hazards from glacier lake outburst floods based on modelling of process cascades at Lake 513, Carhuaz, Peru

2014 ◽  
Vol 35 ◽  
pp. 145-155 ◽  
Author(s):  
D. Schneider ◽  
C. Huggel ◽  
A. Cochachin ◽  
S. Guillén ◽  
J. García
Keyword(s):  
Numerical Models ◽  
Mass Movement ◽  
Field Work ◽  
High Mountain ◽  
Mountain Environments ◽  
The Andes ◽  
Recent Warming ◽  
Outburst Floods ◽  
Physically Based ◽  
Downstream Communities

Abstract. Recent warming has had enormous impacts on glaciers and high-mountain environments. Hazards have changed or new ones have emerged, including those from glacier lakes that form as glaciers retreat. The Andes of Peru have repeatedly been severely impacted by glacier lake outburst floods in the past. An important recent event occurred in the Cordillera Blanca in 2010 when an ice avalanche impacted a glacier lake and triggered an outburst flood that affected the downstream communities and city of Carhuaz. In this study we evaluate how such complex cascades of mass movement processes can be simulated coupling different physically-based numerical models. We furthermore develop an approach that allows us to elaborate corresponding hazard maps according to existing guidelines for debris flows and based on modelling results and field work.

Accelerating recent mass loss from debris-covered Khumbu Glacier in Nepal, and projected response to climate change by 2200 CE

2020 ◽  
Author(s):  
Ann Rowan ◽  
David Egholm ◽  
Duncan Quincey ◽  
Bryn Hubbard ◽  
Evan Miles ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
High Elevation ◽  
High Mountain ◽  
Glacier Surface ◽  
Ice Flow ◽  
Air Temperatures ◽  
Himalayan Glaciers ◽  
Debris Transport ◽  
The Impact

<p>Thick supraglacial debris covers the ablation areas of many large Himalayan glaciers, particularly those in the Everest region where debris is typically several metres thick. Sustained mass loss from these high-elevation debris-covered glaciers is causing supraglacial debris layers to expand and thicken. However, at the same time, regional satellite observations have demonstrated that debris-covered glaciers in High Mountain Asia are currently losing mass at the same rate as clean-ice glaciers. This greater than expected mass loss—sometimes referred to as the “debris-cover anomaly”—could be due to surface processes that locally enhance ablation, including the formation and decay of ice cliffs and supraglacial ponds.</p><p>We tested the hypothesis that the presence of ice cliffs and supraglacial ponds is responsible for the rapid decay of debris-covered Himalayan glaciers, using a numerical glacier model that includes the feedbacks between debris transport, mass balance and ice flow. We show that parameterising differential ablation processes in our higher-order ice flow model of Khumbu Glacier in Nepal does increase glacier-wide mass loss, but is not sufficient to match the observed glacier surface elevation change between 1984 and 2015 CE. Additional mass balance forcing is required to simulate the remaining mass balance change, which may represent the impact of rising air temperatures on englacial and supraglacial hydrology or englacial ice temperatures. Under a moderate future warming scenario (RCP4.5), Khumbu Glacier is projected to lose 59% of ice volume by 2100 CE, and 94% by 2200 CE accompanied by a dynamic shutdown that causes the death of this iconic glacier by 2160 CE.</p>

scholarly journals Health and sustainability of glaciers in High Mountain Asia

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Evan Miles ◽  
Michael McCarthy ◽  
Amaury Dehecq ◽  
Marin Kneib ◽  
Stefan Fugger ◽  
...  
Keyword(s):  
Current Knowledge ◽  
Field Measurements ◽  
Tien Shan ◽  
High Mountain ◽  
Specific Mass ◽  
Ice Flow ◽  
Ice Volume ◽  
Mass Redistribution ◽  
Glacier Ablation

AbstractGlaciers in High Mountain Asia generate meltwater that supports the water needs of 250 million people, but current knowledge of annual accumulation and ablation is limited to sparse field measurements biased in location and glacier size. Here, we present altitudinally-resolved specific mass balances (surface, internal, and basal combined) for 5527 glaciers in High Mountain Asia for 2000–2016, derived by correcting observed glacier thinning patterns for mass redistribution due to ice flow. We find that 41% of glaciers accumulated mass over less than 20% of their area, and only 60% ± 10% of regional annual ablation was compensated by accumulation. Even without 21st century warming, 21% ± 1% of ice volume will be lost by 2100 due to current climatic-geometric imbalance, representing a reduction in glacier ablation into rivers of 28% ± 1%. The ablation of glaciers in the Himalayas and Tien Shan was mostly unsustainable and ice volume in these regions will reduce by at least 30% by 2100. The most important and vulnerable glacier-fed river basins (Amu Darya, Indus, Syr Darya, Tarim Interior) were supplied with >50% sustainable glacier ablation but will see long-term reductions in ice mass and glacier meltwater supply regardless of the Karakoram Anomaly.

scholarly journals Evaluation of numerical models by FerryBox and fixed platform in situ data in the southern North Sea

Ocean Science ◽  
2015 ◽  
Vol 11 (6) ◽  
pp. 879-896 ◽  
Author(s):  
M. Haller ◽  
F. Janssen ◽  
J. Siddorn ◽  
W. Petersen ◽  
S. Dick
Keyword(s):  
North Sea ◽  
High Frequency ◽  
Numerical Models ◽  
Spatial Scales ◽  
Model Performance ◽  
Eastern Coast ◽  
Southern North Sea ◽  
In Situ Data ◽  
Oyster Ground ◽  
Study Results

Abstract. For understanding and forecasting of hydrodynamics in coastal regions, numerical models have served as an important tool for many years. In order to assess the model performance, we compared simulations to observational data of water temperature and salinity. Observations were available from FerryBox transects in the southern North Sea and, additionally, from a fixed platform of the MARNET network. More detailed analyses have been made at three different stations, located off the English eastern coast, at the Oyster Ground and in the German Bight. FerryBoxes installed on ships of opportunity (SoO) provide high-frequency surface measurements along selected tracks on a regular basis. The results of two operational hydrodynamic models have been evaluated for two different time periods: BSHcmod v4 (January 2009 to April 2012) and FOAM AMM7 NEMO (April 2011 to April 2012). While they adequately simulate temperature, both models underestimate salinity, especially near the coast in the southern North Sea. Statistical errors differ between the two models and between the measured parameters. The root mean square error (RMSE) of water temperatures amounts to 0.72 °C (BSHcmod v4) and 0.44 °C (AMM7), while for salinity the performance of BSHcmod is slightly better (0.68 compared to 1.1). The study results reveal weaknesses in both models, in terms of variability, absolute levels and limited spatial resolution. Simulation of the transition zone between the coasts and the open sea is still a demanding task for operational modelling. Thus, FerryBox data, combined with other observations with differing temporal and spatial scales, can serve as an invaluable tool not only for model evaluation, but also for model optimization by assimilation of such high-frequency observations.

Assessing the options for the operational mapping of the soil moisture content in the European Alps

2021 ◽  
Author(s):  
Felix Greifeneder ◽  
Klaus Haslinger ◽  
Georg Seyerl ◽  
Claudia Notarnicola ◽  
Massimiliano Zappa ◽  
...  
Keyword(s):  
Climate Change ◽  
Soil Moisture ◽  
Temporal Dynamics ◽  
Hydrological Cycle ◽  
Balance Model ◽  
High Mountain ◽  
European Alps ◽  
Entire Area ◽  
Advantages And Disadvantages ◽  
Hourly Data

<p>Soil Moisture (SM) is one of the key observable variables of the hydrological cycle and therefore of high importance for many disciplines, from meteorology to agriculture. This contribution presents a comparison of different products for the mapping of SM. The aim was to identify the best available solution for the operational monitoring of SM as a drought indicator for the entire area of the European Alps, to be applied in the context of the Interreg Alpine Space project, the Alpine Drought Observatory.</p><p>The following datasets were considered: Soil Water Index (SWI) of the Copernicus Global Land Service [1]; ERA5 [2]; ERA5-Land [3]; UERRA MESCAN-SURFEX land-surface component [4]. All four datasets offer a different set of advantages and disadvantages related to their spatial resolution, update frequency and latency. As a reference, modelled SM time-series for 307 catchments in Switzerland were used [5]. Switzerland is well suited as a test case for the Alps, due to its different landscapes, from lowlands to high mountain.</p><p>The intercomparison was based on a correlation analysis of daily absolute SM values and the daily anomalies. Furthermore, the probability to detect certain events, such as persistent dry conditions, was evaluated for each of the SM datasets. First results showed that the temporal dynamics (both in terms of absolute values as well as anomalies) of the re-analysis datasets show a high correlation to the reference. A clear gradient, from the lowlands in the north to the high mountains in the south, with decreasing correlation is evident. The SWI data showed weak correlations to the temporal dynamics of the reference in general. Especially, during spring and the first part of the summer SM is significantly underestimated. This might be related to the influence of snowmelt, which is not taken into account in the two-layer water balance model used to model SM for deeper soil layers. Low coverage in the high mountain areas hampered a thorough comparison with the reference in these areas.</p><p>The results presented here are the foundation for selecting a suitable source for the operational mapping of SM for the Alpine Drought Observatory. The next steps will be to test the potential of MESCAN-SURFEX and ERA5-Land for the downscaling of ERA5 to take advantage of the low latency of ERA5 and the improved spatial detail of the other two datasets.  </p><p>Literature:</p><p>[1]  B. Bauer-marschallinger et al., “Sentinel-1 : Harnessing Assets and Overcoming Obstacles,” IEEE Trans. Geosci. Remote Sens., vol. 57, no. 1, pp. 520–539, 2019, doi: 10.1109/TGRS.2018.2858004.</p><p>[2]  H. Hersbach et al., “ERA5 hourly data on single levels from 1979 to present.” Copernicus Climate Change Service (C3S) Climate Data Store (CDS), 2018.</p><p>[3]  Copernicus Climate Change Service, “ERA5-Land hourly data from 2001 to present.” ECMWF, 2019, doi: 10.24381/CDS.E2161BAC.</p><p>[4]  E. Bazile, et al., “MESCAN-SURFEX Surface Analysis. Deliverable D2.8 of the UERRA Project,” 2017. Accessed: Jan. 11, 2020. [Online]. Available: http://www.uerra.eu/publications/deliverable-reports.html.</p><p>[5]  Brunner, et al.: Extremeness of recent drought events in    Switzerland: dependence on variable and return period choice, Nat. Hazards Earth Syst. Sci., 19, 2311–2323, https://doi.org/10.5194/nhess-19-2311-2019, 2019.</p>

Recent Atmospheric Variability at Kibo Summit, Kilimanjaro, and Its Relation to Climate Mode Activity

2018 ◽  
Vol 31 (10) ◽  
pp. 3875-3891 ◽  
Author(s):  
Emily Collier ◽  
Thomas Mölg ◽  
Tobias Sauter
Keyword(s):  
Indian Ocean ◽  
Current Knowledge ◽  
Southern Oscillation ◽  
Strong Association ◽  
Atmospheric Modeling ◽  
High Mountain ◽  
Atmospheric Variability ◽  
Rain Season ◽  
The Indian Ocean ◽  
The Impact

Abstract Accurate knowledge of the impact of internal atmospheric variability is required for the detection and attribution of climate change and for interpreting glacier records. However, current knowledge of such impacts in high-mountain regions is largely based on statistical methods, as the observational data required for process-based assessments are often spatially or temporally deficient. Using a case study of Kilimanjaro, 12 years of convection-permitting atmospheric modeling are combined with an 8-yr observational record to evaluate the impact of climate oscillations on recent high-altitude atmospheric variability during the short rains (the secondary rain season in the region). The focus is on two modes that have a well-established relationship with precipitation during this season, El Niño–Southern Oscillation and the Indian Ocean zonal mode, and demonstrate their strong association with local and mesoscale conditions at Kilimanjaro. Both oscillations correlate positively with humidity fluctuations, but the association is strongest with the Indian Ocean zonal mode in the air layers near and above the glaciers because of changes in zonal circulation and moisture transport, emphasizing the importance of the moisture signal from this basin. However, the most anomalous conditions are found during co-occurring positive events because of the combined effects of the (i) extended positive sea surface temperature anomalies, (ii) enhanced atmospheric moisture capacity from higher tropospheric temperatures, (iii) most pronounced weakening of the subsiding branch of the Indian Ocean Walker circulation over East Africa, and (iv) stronger monsoonal moisture fluxes upstream from Kilimanjaro. This study lays the foundation for unraveling the contribution of climate modes to observed changes in Kilimanjaro’s glaciers.

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