| 1. |
- Abdel-Fattah, Dina, et al.
(author)
-
Application of a structured decision-making process in cryospheric hazard planning : Case study of Bering Glacier surges on local state planning in Alaska
- 2024
-
In: Journal of Multi-Criteria Decision Analysis. - 1057-9214 .- 1099-1360. ; 31:1-2
-
Journal article (peer-reviewed)abstract
- Surging glaciers are glaciers that experience rapidly accelerated glacier flow over a comparatively short period of time. Though relatively rare worldwide, Alaska is home to the largest number of surge-type glaciers globally. However, their impact on the broader socioecological system in the state is both poorly understood and under-researched, which poses a challenge in developing appropriate sustainability decisions in Alaska. We investigated how the surge patterns of the Bering Glacier in Alaska have potentially devastating effects on the local ecological biodiversity of its watershed via a structured decision-making analysis of the different possible consequences. Specifically, this analysis was conducted to explore the various outcomes of a Bering Glacier surge particularly if humans have an increased presence near the glacier due to the area potentially becoming a state park. This work explored the benefits of applying a risk and decision analytical framework in a cryosphere context, to better understand the socioeconomic impact of glacier surges. This is a novel approach in which a decision analysis tool was used to better understand an environmental sustainability challenge, offering an innovative method to support the achievement of the United Nations Sustainability Development Goals in Alaska. We therefore emphasise the need for integrated biophysical and socioeconomic analyses when it comes to understanding glacier hazards. Our research highlights the importance of understanding and researching biophysical changes as well as using a structured decision-making process for complicated hazard planning scenarios, exemplified via glaciated regions in Alaska, in order to create adaptation strategies that are sustainable and encompass the range of possible outcomes.
|
|
| 2. |
- Arendt, Anthony A., et al.
(author)
-
Glacier changes in Alaska : can mass-balance models explain GRACE mascon trends?
- 2009
-
In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 50:50, s. 148-154
-
Journal article (peer-reviewed)abstract
- Temperature and precipitation data from three weather stations in the St Elias Mountains of Alaska and northwestern Canada were used to drive one-dimensional (1-D) (elevation-dependent) and 0-D degree-day mass-balance models. Model outputs were optimized against a 10 day resolution time series of mass variability during 2003-07 obtained from Gravity Recovery and Climate Experiment (GRACE) mass concentration (mascon) solutions. The models explained 52-60% of the variance in the GRACE time series. Modelled mass variations matched the phase of the GRACE observations, and all optimized model parameters were within the range of values determined from conventional mass-balance and meteorological observations. We describe a framework for selecting appropriate weather stations and mass-balance models to represent glacier variations of large regions. There is potential for extending these calibrated mass-balance models forwards or backwards in time to construct mass-balance time series outside of the GRACE measurement window.
|
|
| 3. |
|
|
| 4. |
- Bliss, Andrew, et al.
(author)
-
A new inventory of mountain glaciers and ice caps for the Antarctic periphery
- 2013
-
In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 54:63, s. 191-199
-
Journal article (peer-reviewed)abstract
- Although the glaciers in the Antarctic periphery make up a large fraction of all mountain glaciers and ice caps on Earth, a detailed glacier inventory of the region is lacking. We compile such an inventory, recording areas, area-altitude distributions, terminus characteristics and volume estimates. Glaciers on the mainland are excluded. The inventory is derived from the Antarctic Digital Database and some manual digitization. We additionally rely on satellite imagery, digital elevation models and a flowshed algorithm to classify ice bodies. We find 1133 ice caps and 1619 mountain glaciers covering a total of 132 867 +/- 6643 km(2). Estimated total volume corresponds to 0.121 +/- 0.010 m sea-level equivalent. Of the total glacier area, 99% drains either into ice shelves (63%) or into the ocean (36%). The inventory will provide a database for glacier mass-balance assessments, modelling and projections, and help to reduce the uncertainties in previous studies.
|
|
| 5. |
- Bliss, Andrew, et al.
(author)
-
Global response of glacier runoff to twenty-first century climate change
- 2014
-
In: J GEOPHYS RES-EARTH. - 2169-9003. ; 119:4, s. 717-730
-
Journal article (peer-reviewed)abstract
- The hydrology of many important river systems in the world is influenced by the presence of glaciers in their upper reaches. We assess the global-scale response of glacier runoff to climate change, where glacier runoff is defined as all melt and rain water that runs off the glacierized area without refreezing. With an elevation-dependent glacier mass balance model, we project monthly glacier runoff for all mountain glaciers and ice caps outside Antarctica until 2100 using temperature and precipitation scenarios from 14 global climate models. We aggregate results for 18 glacierized regions. Despite continuous glacier net mass loss in all regions, trends in annual glacier runoff differ significantly among regions depending on the balance between increased glacier melt and reduction in glacier storage as glaciers shrink. While most regions show significant negative runoff trends, some regions exhibit steady increases in runoff (Canadian and Russian Arctic), or increases followed by decreases (Svalbard and Iceland). Annual glacier runoff is dominated by melt in most regions, but rain is a major contributor in the monsoon-affected regions of Asia and maritime regions such as New Zealand and Iceland. Annual net glacier mass loss dominates total glacier melt especially in some high-latitude regions, while seasonal melt is dominant in wetter climate regimes. Our results highlight the variety of glacier runoff responses to climate change and the need to include glacier net mass loss in assessments of future hydrological change.
|
|
| 6. |
- Braun, Matthias, et al.
(author)
-
Comparison of remote sensing derived glacier facies maps with distributed mass balance modelling at Engabreen, northern Norway
- 2007
-
In: Glacier Mass Balance Changes and Meltwater Discharge. - Wallingford : IAHS. - 9781901502398 ; , s. 126-134:318, s. 126-134
-
Conference paper (peer-reviewed)abstract
- Calibration and validation of glacier mass balance models typically rely on mass balance data derived from measurements at individual points, often along altitudinal gradients, thus neglecting much of the spatial variability of mass balance. Remote sensing data can provide useful additional spatially distributed information, e.g. on surface conditions such as bare ice area, firn cover extent, or snow. We developed a semi-automated procedure to derive glacier-facies maps from Landsat satellite images, and applied it to Engabreen, an outlet glacier from the Svartisen ice cap in northern Norway. These maps, discriminating between firn, snow and ice surfaces, are then used as a reference for mass balance modelling. Facies information shows a general agreement with the available few field observations and results obtained by distributed mass balance modelling. We conclude that Earth Observation products provide a powerful, although as yet poorly exploited tool, for calibration and validation of distributed mass balance models.
|
|
| 7. |
- Das, Indrani, et al.
(author)
-
21st-century increase in glacier mass loss in the Wrangell Mountains, Alaska, USA, from airborne laser altimetry and satellite stereo imagery
- 2014
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:220, s. 283-293
-
Journal article (peer-reviewed)abstract
- Alaskan glaciers are among the largest regional contributors to sea-level rise in the latter half of the 20th century. Earlier studies have documented extensive and accelerated ice wastage in most regions of Alaska. Here we study five decades of mass loss on high-elevation, land-terminating glaciers of the Wrangell Mountains (similar to 4900 km(2)) in central Alaska based on airborne center-line laser altimetry data from 2000 and 2007, a digital elevation model (DEM) from ASTER and SPOT5, and US Geological Survey topographic maps from 1957. The regional mass-balance estimates derived from center-line laser altimetry profiles using two regional extrapolation techniques agree well with that from DEM differencing. Repeat altimetry measurements reveal accelerated mass loss over the Wrangell Mountains, with the regional mass-balance rate evolving from -0.07 +/- 0.19 m w.e. a(-1) during 1957-2000 to -0.24 +/- 0.16 m w.e. a(-1) during 2000-07. Nabesna, the largest glacier in this region (similar to 1056 km(2)), lost mass four times faster during 2000-07 than during 1957-2000. Although accelerated, the mass change over this region is slower than in other glacierized regions of Alaska, particularly those with tidewater glaciers. Together, our laser altimetry and satellite DEM analyses demonstrate increased wastage of these glaciers during the last 50 years.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- de Woul, Mattias, 1972-
(author)
-
Response of glaciers to climate change : Mass balance sensitivity, sea level rise and runoff
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- The purpose of this study is to enhance our understanding of the response of glaciers to climate change. Global sea level is affected by changes in glacier ice volume, and melt-water from glaciers is a principal water source in many regions. This study applies glacier mass balance modelling, with varying complexity and spatial resolution, ranging from individual glaciers to regional and global assessments of glacier mass losses. Glaciers located in maritime environments generally show considerably higher mass balance sensitivities than those in continental settings. On average, an assumed increase in annual precipitation of +10% tends to offset the effect of an annual temperature change of +1 K, by roughly 20%. Two case studies, at Storglaciären, Sweden, and Hofsjökull, Iceland, involve model results of future mass balance change and glacier melt induced changes in runoff. Applying a temperature and precipitation scenario for Iceland in 2050 results in increased total runoff from Hofsjökull by roughly one third, and results emphasize the role of the firn layer in delaying water flow through glaciers, yielding a redistribution of discharge within the year. Based on a global gridded data set of glacierized area, the sea level equivalent from all mountain glaciers and ice caps outside the ice sheets in Greenland and Antarctica during 1961–2004, caused by changes in temperature and precipitation, is estimated to be 0.58±0.34 mm a–1. The mountain glaciers and ice caps around Antarctica alone contribute almost 40% of the global estimate, and hence their contribution is considerably larger than previously assumed.
|
|
| 13. |
|
|
| 14. |
- Gardner, Alex S., et al.
(author)
-
A Reconciled Estimate of Glacier Contributions to Sea Level Rise : 2003 to 2009
- 2013
-
In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 340:6134, s. 852-857
-
Journal article (peer-reviewed)abstract
- Glaciers distinct from the Greenland and Antarctic Ice Sheets are losing large amounts of water to the world's oceans. However, estimates of their contribution to sea level rise disagree. We provide a consensus estimate by standardizing existing, and creating new, mass-budget estimates from satellite gravimetry and altimetry and from local glaciological records. In many regions, local measurements are more negative than satellite-based estimates. All regions lost mass during 2003-2009, with the largest losses from Arctic Canada, Alaska, coastal Greenland, the southern Andes, and high-mountain Asia, but there was little loss from glaciers in Antarctica. Over this period, the global mass budget was -259 +/- 28 gigatons per year, equivalent to the combined loss from both ice sheets and accounting for 29 +/- 13% of the observed sea level rise.
|
|
| 15. |
- Harrison, W., et al.
(author)
-
Implications for the dynamic health of a glacier from comparison of conventional and reference-surface balances
- 2009
-
In: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 50:50, s. 25-30
-
Journal article (peer-reviewed)abstract
- Conventional and reference-surface mass-balance data from Gulkana and Wolverine Glaciers, Alaska, USA, are used to address the questions of how rapidly these glaciers are adjusting (or 'responding') to climate, whether their responses are stable, and whether the glaciers are likely to survive in today's climate. Instability means that a glacier will eventually vanish, or at least become greatly reduced in volume, if the climate stabilizes at its present state. A simple non-linear theory of response is presented for the analysis. The response of Gulkana Glacier is characterized by a timescale of several decades, but its stability and therefore its survival in today's climate are uncertain. Wolverine seems to be responding to climate more slowly, on the timescale of one to several centuries. Its stability is also uncertain, but a slower response time would make it more susceptible to climate changes.
|
|
| 16. |
- Hock, Regine, et al.
(author)
-
Climate sensitivity of Storglaciären, Sweden : an intercomparison of mass-balance models using ERA-40 re-analysis and regional climate model data
- 2007
-
In: Annals of glaciology, Vol 46, 2007. - : International Glaciological Society. - 9780946417414 ; 46:1, s. 342-348
-
Conference paper (peer-reviewed)abstract
- Estimates of glacier contributions to future sea-level rise are often computed from mass-balance sensitivities derived for a set of representative glaciers. Our purpose is to investigate how mass-balance projections and sensitivities vary when using different approaches to compute the glacier mass balance. We choose Storglaciären, Sweden, as a test site and apply five different models including temperature-index and energy-balance approaches further varying in spatial discretization. The models are calibrated using daily European Centre for Medium-Range Weather Forecasts re-analysis (ERA-40) data. We compute static mass-balance sensitivities and cumulative mass balances until 2100 based on daily temperatures predicted by a regional climate model. Net mass-balance sensitivities to a +1 K perturbation and a 10% increase in precipitation spanned from −0.41 to −0.61 and from 0.19 to 0.22 m a−1, respectively. The cumulative mass balance for the period 2002-2100 in response to the climate-model predicted temperature changes varied between −81 and −92 m for four models, but was −121 m for the fully distributed detailed energy-balance model. This indicates that mass losses may be underestimated if temperature-index methods are used instead of detailed energy-balance approaches that account for the effects of temperature changes on all energy-balance components individually. Our results suggest that future glacier predictions are sensitive to the choice of the mass-balance model broadening the spectrum in uncertainties.
|
|
| 17. |
- Hock, Regine, et al.
(author)
-
Deriving glacier mass balance from accumulation area ratio on Storglaciären, Sweden
- 2007
-
In: Glacier Mass Balance Changes and Meltwater Discharge. - Wallingford : IAHS. ; , s. 163-170
-
Conference paper (peer-reviewed)abstract
- Glacier net mass balance, bn, tends to correlate well with accumulation area ratio (AAR). A method that substitutes the long-term bn - AAR relationship by the transient relationship, derived from repeated measurements during one ablation season, is tested on Storglaciären, a well-investigated glacier in Sweden. We use the 1946 – 2004 long-term record, transient mass balance measurements in 2004 and results from a distributed energy-balance mass-balance model. The long-term and transient relationships are in good agreement for negative and slightly positive mass balances corresponding to AAR of roughly 0.2 to 0.6 but progressively deviate from each other with increasing net balances and larger AARs. The modelling indicates that the deviation becomes smaller as winter mass balance increases. It is concluded that the transient bn,t – AARt relationship should (a) be established during a highly negative mass balance year and (b) exclude any data from the earlier part of the melt season. Deriving the relationship from mass balance modelling may provide a powerful alternative circumventing the need for a highly negative mass balance year for the transient measurements.
|
|
| 18. |
- Hock, Regine, 1960-, et al.
(author)
-
GlacierMIP - A model intercomparison of global-scale glacier mass-balance models and projections
- 2019
-
In: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 65:251, s. 453-467
-
Journal article (peer-reviewed)abstract
- Global-scale 21st-century glacier mass change projections from six published global glacier models are systematically compared as part of the Glacier Model Intercomparison Project. In total 214 projections of annual glacier mass and area forced by 25 General Circulation Models (GCMs) and four Representative Concentration Pathways (RCP) emission scenarios and aggregated into 19 glacier regions are considered. Global mass loss of all glaciers (outside the Antarctic and Greenland ice sheets) by 2100 relative to 2015 averaged over all model runs varies from 18 +/- 7% (RCP2.6) to 36 +/- 11% (RCP8.5) corresponding to 94 +/- 25 and 200 +/- 44 mm sea-level equivalent (SLE), respectively. Regional relative mass changes by 2100 correlate linearly with relative area changes. For RCP8.5 three models project global rates of mass loss (multi-GCM means) of >3 mm SLE per year towards the end of the century. Projections vary considerably between regions, and also among the glacier models. Global glacier mass changes per degree global air temperature rise tend to increase with more pronounced warming indicating that mass-balance sensitivities to temperature change are not constant. Differences in glacier mass projections among the models are attributed to differences in model physics, calibration and downscaling procedures, initial ice volumes and varying ensembles of forcing GCMs.
|
|
| 19. |
|
|
| 20. |
- Hock, Regine, et al.
(author)
-
Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution
- 2009
-
In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:L07501
-
Journal article (peer-reviewed)abstract
- The Intergovernmental Panel on Climate Change (IPCC) estimates that the sum of all contributions to sea‐level rise for the period 1961–2004 was 1.1 ± 0.5 mm a−1, leaving 0.7 ± 0.7 of the 1.8 ± 0.5 mm a−1 observed sea‐level rise unexplained. Here, we compute the global surface mass balance of all mountain glaciers and ice caps (MG&IC), and find that part of this much‐discussed gap can be attributed to a larger contribution than previously assumed from mass loss of MG&IC, especially those around the Antarctic Peninsula. We estimate global surface mass loss of all MG&IC as 0.79 ± 0.34 mm a−1 sea‐level equivalent (SLE) compared to IPCC's 0.50 ± 0.18 mm a−1. The Antarctic MG&IC contributed 28% of the global estimate due to exceptional warming around the Antarctic Peninsula and high sensitivities to temperature similar to those we find in Iceland, Patagonia and Alaska.
|
|
| 21. |
- Hulth, John, et al.
(author)
-
Estimating glacier snow accumulation from backward calculation of melt and snowline tracking
- 2013
-
In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 54:62, s. 1-7
-
Journal article (peer-reviewed)abstract
- Estimating precipitation to determine accumulation is challenging. We present a method that combines melt modelling and snowline tracking to determine winter glacier snow accumulation along snowlines. The method assumes that the net accumulation is zero on the transient snowlines and the maximum winter accumulation at the snowline can be calculated backwards with a temperature-index melt model. To verify the method, the accumulation model is applied for the year 2004 on Storglaciaren, Sweden, for which extensive meteorological and mass-balance data are available. The measured mean snowline accumulation is 0.94 +/- 0.10 m w.e. for 2004. Modelled accumulation, using backward melt modelling, at the same snowlines is 0.82 +/- 0.25 m w.e. The accumulation model is also compared with an often used linear regression accumulation model which yields a mean snowline accumulation of 1.02 +/- 0.38 m w.e. The reduction in standard error from 0.38 m w.e. to 0.25 m w.e. shows that the backward melt modelling applied at snowlines can provide a better spatial representation of the accumulation pattern than the regression model. Importantly, the applied method requires no field measurements of accumulation during the winter and snowlines can be readily traced in remotely sensed images.
|
|
| 22. |
- Huss, Matthias, et al.
(author)
-
100-year mass changes in the Swiss Alps linked to the Atlantic Multidecadal Oscillation
- 2010
-
In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37, s. L10501-
-
Journal article (peer-reviewed)abstract
- Thirty new 100-year records of glacier surface mass balance, accumulation and melt in the Swiss Alps are presented. The time series are based on a comprehensive set of field data and distributed modeling and provide insights into the glacier-climate linkage. Considerable mass loss over the 20th century is evident for all glaciers, but rates differ strongly. Glacier mass loss shows multidecadal variations and was particularly rapid in the 1940s and since the 1980s. Mass balance is significantly anticorrelated to the Atlantic Multidecadal Oscillation (AMO) index assumed to be linked to thermohaline ocean circulation. We show that North Atlantic variability had a recognizable impact on glacier changes in the Swiss Alps for at least 250 years.
|
|
| 23. |
- Huss, Matthias, et al.
(author)
-
A new model for global glacier change and sea-level rise
- 2015
-
In: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 3
-
Journal article (peer-reviewed)abstract
- The anticipated retreat of glaciers around the globe will pose far-reaching challenges to the management of fresh water resources and significantly contribute to sea-level rise within the coming decades. Here, we present a new model for calculating the twenty-first century mass changes of all glaciers on Earth outside the ice sheets. The Global Glacier Evolution Model (GloGEM) includes mass loss due to frontal ablation at marine-terminating glacier fronts and accounts for glacier advance/retreat and surface elevation changes. Simulations are driven with monthly near-surface air temperature and precipitation from 14 Global Circulation Models forced by RCP2.6, RCP4.5, and RCP8.5 emission scenarios. Depending on the scenario, the model yields a global glacier volume loss of 25–48% between 2010 and 2100. For calculating glacier contribution to sea-level rise, we account for ice located below sea-level presently displacing ocean water. This effect reduces the glacier contribution by 11–14%, so that our model predicts a sea-level equivalent (multi-model mean ±1 standard deviation) of 79±24 mm (RCP2.6), 108±28 mm (RCP4.5), and 157±31 mm (RCP8.5). Mass losses by frontal ablation account for 10% of total ablation globally, and up to ∼30% regionally. Regional equilibrium line altitudes are projected to rise by ∼100–800 m until 2100, but the effect on ice wastage depends on initial glacier hypsometries.
|
|
| 24. |
- Huss, Matthias, et al.
(author)
-
Conventional versus reference-surface mass balance
- 2012
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:208, s. 278-286
-
Journal article (peer-reviewed)abstract
- Glacier surface mass balance evaluated over the actual glacier geometry depends not only on climatic variations, but also on the dynamic adjustment of glacier geometry. Therefore, it has been proposed that reference-surface balances calculated over a constant glacier hypsometry are better suited for climatic interpretation. Here we present a comparison of 82 year modelled time series (1926-2008) of conventional and reference-surface balance for 36 Swiss glaciers. Over this time period the investigated glaciers have lost 22% of their area, and ice surface elevation close to the current glacier terminus has decreased by 78 m on average. Conventional balance in the last decade, at -0.91 m w.e.a(-1), is 0.14 m w.e.a(-1) less negative than the reference-surface balance. About half of the negative (stabilizing) feedback on mass balance due to glacier terminus retreat is compensated by more negative mass balances due to surface lowering. Short-term climatic variability is clearly reflected in the conventional mass-balance series; however, the magnitude of the long-term negative trend is underestimated compared to that found in the reference-surface balance series. Both conventional and reference-surface specific balances show large spatial variability among the 36 glaciers.
|
|
| 25. |
- Huss, M., et al.
(author)
-
Determination of the seasonal mass balance of four Alpine glaciers since 1865
- 2008
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:F1, s. F01015-
-
Journal article (peer-reviewed)abstract
- Alpine glaciers have suffered major losses of ice in the last century. We compute spatially distributed seasonal mass balances of four glaciers in the Swiss Alps (Grosser Aletschgletscher, Rhonegletscher, Griesgletscher and Silvrettagletscher) for the period 1865 to 2006. The mass balance model is forced by daily air temperature and precipitation data compiled from various long-term data series. The model is calibrated using ice volume changes derived from five to nine high-resolution digital elevation models, annual discharge data and a newly compiled data set of more than 4000 in situ measurements of mass balance covering different subperiods. The cumulative mass balances over the 142 year period vary between -35 and -97 m revealing a considerable mass loss. There is no significant trend in winter balances, whereas summer balances display important fluctuations. The rate of mass loss in the 1940s was higher than in the last decade. Our approach combines different types of field data with mass balance modeling to resolve decadal scale ice volume change observations to seasonal and spatially distributed mass balance series. The results contribute to a better understanding of the climatic forcing on Alpine glaciers in the last century.
|
|
| 26. |
- Huss, Matthias, et al.
(author)
-
Glacier-dammed lake outburst events of Gornersee, Switzerland
- 2007
-
In: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 53:181, s. 189-200
-
Journal article (peer-reviewed)abstract
- Gornersee is an ice marginal lake, which drains almost every year subglacially within a few days. We present an analysis of the lake outburst events between 1950 and 2005, as well as results of detailed field investigations related to the lake drainage in 2004 and 2005. The latter included measurements of lake geometry, water pressure in nearby boreholes, and glacier surface motion. A distributed temperature-index melt model coupled to a linear-reservoir runoff model is used to calculate hourly discharge from the catchment of Gornergletscher in order to distinguish between the melt-precipitation component and the outburst component of the discharge hydrograph. In this way, drainage volume and timing are determined. There is a clear trend since 1950 for the outburst flood to occur earlier in the melt season, though lacking any relation to lake discharge volumes. Peak discharges from the lake lie significantly below the values obtained with the empirical relation proposed by Clague and Mathews (1973). The shapes of the 2004 and 2005 lake outflow hydrographs differ substantially, thereby suggesting different drainage mechanisms. From water balance onsiderations we infer a leakage of the glacier-dammed lake starting one week prior to the lake outburst in 2005. During the drainage events up to 50% of lake water is temporarily stored in the glacial system causing substantial uplifts of the glacier surface.
|
|
| 27. |
- Huss, Matthias, et al.
(author)
-
Global-scale hydrological response to future glacier mass loss
- 2018
-
In: Nature Climate Change. - : NATURE PUBLISHING GROUP. - 1758-678X .- 1758-6798. ; 8:2, s. 135-140
-
Journal article (peer-reviewed)abstract
- Worldwide glacier retreat and associated future runoff changes raise major concerns over the sustainability of global water resources(1-4), but global-scale assessments of glacier decline and the resulting hydrological consequences are scarce(5,6). Here we compute global glacier runoff changes for 56 large-scale glacierized drainage basins to 2100 and analyse the glacial impact on streamflow. In roughly half of the investigated basins, the modelled annual glacier runoff continues to rise until a maximum ('peak water') is reached, beyond which runoff steadily declines. In the remaining basins, this tipping point has already been passed. Peak water occurs later in basins with larger glaciers and higher ice-cover fractions. Typically, future glacier runoff increases in early summer but decreases in late summer. Although most of the 56 basins have less than 2% ice coverage, by 2100 one-third of them might experience runoff decreases greater than 10% due to glacier mass loss in at least one month of the melt season, with the largest reductions in central Asia and the Andes. We conclude that, even in large-scale basins with minimal ice-cover fraction, the downstream hydrological effects of continued glacier wastage can be substantial, but the magnitudes vary greatly among basins and throughout the melt season.
|
|
| 28. |
- Jonsell, Ulf, et al.
(author)
-
Recent air and ground temperature increases at Tarfala Research Station, Sweden
- 2013
-
In: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 32:UNSP 19807
-
Journal article (peer-reviewed)abstract
- Long-term data records are essential to detect and understand environmental change, in particular in generally data-sparse high-latitude and high-altitude regions. Here, we analyse a 47-year air temperature record (1965 2011) at Tarfala Research Station (67 degrees 54.7'N, 18 degrees 36.7'E, 1135 m a.s.l.) in northern Sweden, and a nearby 11-year record of 100-m-deep ground temperature (2001-11; 1540 m a.s.l.). The air temperature record shows a mean annual air temperature of -3.5 +/- 0.9 degrees C (+/- 1 standard deviation sigma) and a linear warming trend of +/- 0.042 degrees C yr(-1). The warming trend shows large month-to-month variations with the largest trend in January followed by October. Also, the number of days with positive mean daily temperatures and positive degree-day sums has increased during the last two decades compared to the previous period. Temperature lapse rates derived from the mean daily Tarfala record and an air temperature record at the borehole site average 4.5 degrees C km(-1) and tend to be higher in summer than in winter. Mean summer air temperatures at Tarfala explain 76% of the variance of the summer glacier mass balance of nearby Storglaciaren. Consistent with the observed increase in Tarfala's air temperature, the ground temperature record shows significant permafrost warming with the largest trend (0.047 degrees C yr(-1)) found at 20 m depth.
|
|
| 29. |
- Kienholz, C., et al.
(author)
-
A new method for deriving glacier centerlines applied to glaciers in Alaska and northwest Canada
- 2014
-
In: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 8:2, s. 503-519
-
Journal article (peer-reviewed)abstract
- This study presents a new method to derive centerlines for the main branches and major tributaries of a set of glaciers, requiring glacier outlines and a digital elevation model (DEM) as input. The method relies on a "cost grid-least-cost route approach" that comprises three main steps. First, termini and heads are identified for every glacier. Second, centerlines are derived by calculating the least-cost route on a previously established cost grid. Third, the centerlines are split into branches and a branch order is allocated. Application to 21 720 glaciers in Alaska and northwest Canada (Yukon, British Columbia) yields 41 860 centerlines. The algorithm performs robustly, requiring no manual adjustments for 87.8% of the glaciers. Manual adjustments are required primarily to correct the locations of glacier heads (7.0% corrected) and termini (3.5% corrected). With corrected heads and termini, only 1.4% of the derived centerlines need edits. A comparison of the lengths from a hydrological approach to the lengths from our longest centerlines reveals considerable variation. Although the average length ratio is close to unity, only similar to 50% of the 21 720 glaciers have the two lengths within 10% of each other. A second comparison shows that our centerline lengths between lowest and highest glacier elevations compare well to our longest centerline lengths. For > 70% of the 4350 glaciers with two or more branches, the two lengths are within 5% of each other. Our final product can be used for calculating glacier length, conducting length change analyses, topological analyses, or flowline modeling.
|
|
| 30. |
- Kienholz, Christian, et al.
(author)
-
A new semi-automatic approach for dividing glacier complexes into individual glaciers
- 2013
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:217, s. 925-937
-
Journal article (peer-reviewed)abstract
- Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semi-automatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of similar to 1300 glaciers were misclassified. The algorithm was validated on >25 000 km(2) of ice in other regions in Alaska and on >40 000 km(2) of ice in Arctic Canada, resulting in similar to 2% and similar to 3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.
|
|
| 31. |
- Kienholz, Christian, et al.
(author)
-
Derivation and analysis of a complete modern-date glacier inventory for Alaska and northwest Canada
- 2015
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 61:227, s. 403-420
-
Journal article (peer-reviewed)abstract
- We present a detailed, complete glacier inventory for Alaska and neighboring Canada using multi-sensor satellite data from 2000 to 2011. For each glacier, we derive outlines and 51 variables, including center-line lengths, outline types and debris cover. We find 86 723 km(2) of glacier area (27 109 glaciers >0.025 km(2)), similar to 12% of the global glacierized area outside ice sheets. Of this area 12.0% is drained by 39 marine-terminating glaciers (74 km of tidewater margin), and 19.3% by 148 lake- and river-terminating glaciers (420 km of lake-/river margin). The overall debris cover is 11%, with considerable differences among regions, ranging from 1.4% in the Kenai Mountains to 28% in the Central Alaska Range. Comparison of outlines from different sources on >2500 km(2) of glacierized area yields a total area difference of similar to 10%, emphasizing the difficulties in accurately delineating debris-covered glaciers. Assuming fully correlated (systematic) errors, uncertainties in area reach 6% for all Alaska glaciers, but further analysis is needed to explore adequate error correlation scales. Preliminary analysis of the glacier database yields a new set of well-constrained area/length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries. The new glacier database will be valuable to further explore relations between glacier variables and glacier behavior.
|
|
| 32. |
- Kienholz, C., et al.
(author)
-
Geodeticmass balance of surge-type Black Rapids Glacier, Alaska, 1980-2001-2010, including role of rockslide deposition and earthquake displacement
- 2016
-
In: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 121:12, s. 2358-2380
-
Journal article (peer-reviewed)abstract
- We determine the geodetic mass balance of surge-type Black Rapids Glacier, Alaska, for the time periods 1980-2001 and 2001-2010 by combining modern interferometric synthetic aperture radar (InSAR)-derived digital elevation models (DEMs), DEMs derived from archival aerial imagery, laser altimetry data, and in situ surface elevation measurements. Our analysis accounts for both the large rockslides and terrain displacements caused by the 2002 M7.9 earthquake on the Denali fault, which runs through Black Rapids Glacier. To estimate uncertainties, we apply Monte Carlo simulations. For the earthquake-triggered rockslides we find a volume of 56.62 +/- 2.86 x 10(6) m(3), equivalent to an average debris thickness of 4.44 +/- 0.24 m across the 11.7 km(2) deposit area on the glacier. Terrain displacement due to the earthquake corresponds to an apparent glacier volume change of -53.1 x 106 m(3), which would cause an apparent specific mass balance of -0.19 meter water equivalent (mwe) if not taken into account. The geodetic mass balance of Black Rapids Glacier is -0.48 +/- 0.07 mwe a(-1) for the entire 30 year period, but more negative for the period 2001-2010 (-0.64 +/- 0.11 mwe a(-1)) than the period 1980-2001 (-0.42 +/- 0.11 mwe a(-1)), in agreement with trends indicated by in situ mass balance measurements. Elevation data indicate no net thickening of the surge reservoir between 1980 and 2010, in contrast to what is expected during the quiescent phase. A surge of Black Rapids Glacier in the near future is thus considered unlikely.
|
|
| 33. |
- Kienholz, Christian, et al.
(author)
-
Mass Balance Evolution of Black Rapids Glacier, Alaska, 1980-2100, and Its Implications for Surge Recurrence
- 2017
-
In: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 5
-
Journal article (peer-reviewed)abstract
- Surge-type Black Rapids Glacier, Alaska, has undergone strong retreat since it last surged in 1936-1937. To assess its evolution during the late Twentieth and Twenty-first centuries and determine potential implications for surge likelihood, we run a simplified glacier model over the periods 1980-2015 (hindcasting) and 2015-2100 (forecasting). The model is forced by daily temperature and precipitation fields, with downscaled reanalysis data used for the hindcasting. A constant climate scenario and an RCP 8.5 scenario based on the GFDL-CM3 climate model are employed for the forecasting. Debris evolution is accounted for by a debris layer time series derived from satellite imagery (hindcasting) and a parametrized debris evolution model (forecasting). A retreat model accounts for the evolution of the glacier geometry. Model calibration, validation and parametrization rely on an extensive set of in situ and remotely sensed observations. To explore uncertainties in our projections, we run the glacier model in a Monte Carlo fashion, varying key model parameters and input data within plausible ranges. Our results for the hindcasting period indicate a negative mass balance trend, caused by atmospheric warming in the summer, precipitation decrease in the winter and surface elevation lowering (climate-elevation feedback), which exceed the moderating effects from increasing debris cover and glacier retreat. Without the 2002 rockslide deposits on Black Rapids' lower reaches, the mass balances would be more negative, by similar to 20% between the 2003 and 2015 mass-balance years. Despite its retreat, Black Rapids Glacier is substantially out of balance with the current climate. By 2100, similar to 8% of Black Rapids' 1980 area are projected to vanish under the constant climate scenario and similar to 73% under the RCP 8.5 scenario. For both scenarios, the remaining glacier portions are out of balance, suggesting continued retreat after 2100. Due to mass starvation, a surge in the Twenty-first century is unlikely. The projected retreat will affect the glacier's runoff and change the landscape in the Black Rapids area markedly.
|
|
| 34. |
- Konya, Keiko, et al.
(author)
-
Temperature lapse rates and surface energy balance at Storglaciären, northern Sweden
- 2007
-
In: Glacier Mass Balance Changes and Meltwater Discharge. - Wallingford : IAHS. ; , s. 186-194
-
Conference paper (peer-reviewed)abstract
- A detailed meteorological experiment, including the operation of several automatic weather stations on and outside the glacier, was performed on Storglaciären, a valley glacier in Sweden, in summer 2003. On average, near surface air temperature lapse rates derived from several weather stations on the glacier were –6.0 ± 3.5°C km-1, indicating strong temporal variability. We found no correlation with meteorological variables as a base for param-eterization in melt modelling. Surface energy balance computations showed that, on average, net radiation is the largest contributor to melt energy, in agreement with previous studies. Latent heat fluxes were positive throughout the simulation period indicating condensation. It was not possible to constrain roughness lengths within several orders of magnitudes, since the differences in modelled melt for all cases were still within the range of uncertainty pertinent to the melt measurements during the 13-day period of coincident meteorolo-gical and melt measurements.
|
|
| 35. |
- McNabb, B, et al.
(author)
-
Using surface velocities to infer ice thickness and bed topography : A case study a Columbia Glacier, Alaska, USA
- 2012
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:212, s. 1151-1164
-
Journal article (peer-reviewed)abstract
- Information about glacier volume and ice thickness distribution is essential for manyglaciological applications, but direct measurements of ice thickness can be diffcult and costly. Wepresent a new method that calculates ice thickness via an estimate of ice fux. We solve the familiarcontinuity equation between adjacent fowlines, which decreases the computational time requiredcompared to a solution on the whole grid. We test the method on Columbia Glacier, a large tidewaterglacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results.This shows the potential of this method for estimating ice thickness distribution of glaciers for whichonly surface data are available. We fnd that both the mean thickness and volume of Columbia Glacierwere approximately halved over the period 1957–2007, from 281m to 143m, and from 294km3to134km3, respectively. Using bedrock slope and considering how waves of thickness change propagatethrough the glacier, we conduct a brief analysis of the instability of Columbia Glacier, which leads usto conclude that the rapid portion of the retreat may be nearing an end.
|
|
| 36. |
- McNabb, R. W., et al.
(author)
-
Alaska tidewater glacier terminus positions, 1948-2012
- 2014
-
In: J GEOPHYS RES-EARTH. - 2169-9003. ; 119:2, s. 153-167
-
Journal article (peer-reviewed)abstract
- A significant portion of the world's glacier ice drains through tidewater outlets, though much remains unknown about the response to recent climate change of tidewater glaciers. We present a 64 year record of length change for 50 Alaska tidewater glaciers. We use U.S. Geological Survey topographic maps to provide a base length for glaciers before 1970. Using all available cloud-free Landsat images, we manually digitize calving front outlines for each glacier between 1972 and 2012, resulting in a total of more than 10,000 outlines. Tidewater glacier lengths vary seasonally; focusing on the 36 glaciers terminating in tidewater throughout the study period, we find a mean ( standard deviation) seasonal variation of 60 85m a(-1). We use these oscillations to determine the significance of interannual changes in glacier length. All 36 glaciers underwent at least one period (1 year) of significant advance or retreat; 28 glaciers underwent at least one period of both significant advance and retreat. Over the entire period 1948-2012, 24 of these glaciers retreated a total ( uncertainty) of 107.950.29 km, 11 advanced a total of 7.71 +/- 0.20, and one (Chenega Glacier) did not change significantly. Retreats and advances are highly variable in time; several glaciers underwent rapid, short-term retreats of a few years duration. These retreats occurred after large changes in summer sea surface temperature anomalies; further study is needed to determine what triggered these retreats. No coherent regional behavior signal is apparent in the length record, although two subregions show a coherence similar to recent observations in Greenland. Key Points Alaska tidewater glacier length record, 1948-2012 Tidewater glacier retreat not constant in time Some retreats appear to be triggered by changes in ocean temperature
|
|
| 37. |
- McNabb, R. W., et al.
(author)
-
Variations in Alaska tidewater glacier frontal ablation, 1985-2013
- 2015
-
In: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 120:1, s. 120-136
-
Journal article (peer-reviewed)abstract
- Our incomplete knowledge of the proportion of mass loss due to frontal ablation (the sum of ice loss through calving and submarine melt) from tidewater glaciers outside of the Greenland and Antarctic ice sheets has been cited as a major hindrance to accurate predictions of global sea level rise. We present a 28 year record (1985-2013) of frontal ablation for 27 Alaska tidewater glaciers (representing 96% of the total tidewater glacier area in the region), calculated from satellite-derived ice velocities and modeled estimates of glacier ice thickness. We account for cross-sectional ice thickness variation, long-term thickness changes, mass lost between an upstream fluxgate and the terminus, and mass change due to changes in terminus position. The total mean rate of frontal ablation for these 27 glaciers over the period 1985-2013 is 15.11 3.63Gta(-1). Two glaciers, Hubbard and Columbia, account for approximately 50% of these losses. The regional total ablation has decreased at a rate of 0.14Gta(-1) over this time period, likely due to the slowing and thinning of many of the glaciers in the study area. Frontal ablation constitutes only approximate to 4% of the total annual regional ablation, but roughly 20% of net mass loss. Comparing several commonly used approximations in the calculation of frontal ablation, we find that neglecting cross-sectional thickness variations severely underestimates frontal ablation.
|
|
| 38. |
- Möller, Marco, et al.
(author)
-
Climatic mass balance of the ice cap Vestfonna, Svalbard : A spatially distributed assessment using ERA-Interim and MODIS data
- 2011
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116:F3
-
Journal article (peer-reviewed)abstract
- The ice cap Vestfonna in the northern Svalbard archipelago is one of the largest ice bodies of the European Arctic (similar to 2400 km(2)), but little is known about its mass balance. We model the climatic mass balance of the ice cap for the period September 2000 to August 2009 on a daily basis. Ablation is calculated by a spatially distributed temperature-radiation-index melt model. Air temperature forcing is provided by ERA-Interim data that is downscaled using data from an automatic weather station operated on the ice cap. Spatially distributed net shortwave radiation fluxes are obtained from standard trigonometric techniques combined with Moderate Resolution Imaging Spectroradiometer-based cloud cover and surface albedo information. Accumulation is derived from ERA-Interim precipitation data that are bias corrected and spatially distributed as a function of elevation. Refreezing is incorporated using the P(max) approach. Results indicate that mass balance years are characterized by short ablation seasons (June to August) and correspondingly longer accumulation periods (September to May). The modeled, annual climatic mass balance rate shows an almost balanced mean of -0.02 +/- 0.20 m w.e. yr(-1) (meters water equivalent per year) with an associated equilibrium line altitude of 383 +/- 54 m above sea level (mean +/- one standard deviation). The mean winter balance is +0.32 +/- 0.06 m w.e. yr(-1), and the mean summer balance -0.35 +/- 0.17 m w.e. yr(-1). Roughly one fourth of total surface ablation is retained by refreezing indicating that refreezing is an important component of the mass budget of Vestfonna.
|
|
| 39. |
- Osmanoglu, B., et al.
(author)
-
Surface velocity and ice discharge of the ice cap on King George Island, Antarctica
- 2013
-
In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 54:63, s. 111-119
-
Journal article (peer-reviewed)abstract
- Glaciers on King George Island, Antarctica, have shown retreat and surface lowering in recent decades, concurrent with increasing air temperatures. A large portion of the glacier perimeter is ocean-terminating, suggesting possible large mass losses due to calving and submarine melting. Here we estimate the ice discharge into the ocean for the King George Island ice cap. L-band synthetic aperture radar images covering the time-span January 2008 to January 2011 over King George Island are processed using an intensity-tracking algorithm to obtain surface velocity measurements. Pixel offsets from 40 pairs of radar images are analysed and inverted to estimate a weighted average surface velocity field. Ice thicknesses are derived from simple principles of ice flow mechanics using the computed surface velocity fields and in situ thickness data. The maximum ice surface speeds reach >225 m a(-1), and the total ice discharge for the analysed flux gates of King George Island is estimated to be 0.720 +/- 0.428 Gt a(-1), corresponding to a specific mass loss of 0.64 +/- 0.38 m w.e. a(-1) over the area of the entire ice cap (1127 km(2)).
|
|
| 40. |
- Osmanoglu, B., et al.
(author)
-
Surface velocity and mass balance of Livingston Island ice cap, Antarctica
- 2014
-
In: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 8:5, s. 1807-1823
-
Journal article (peer-reviewed)abstract
- The mass budget of the ice caps surrounding the Antarctica Peninsula and, in particular, the partitioning of its main components are poorly known. Here we approximate frontal ablation (i.e. the sum of mass losses by calving and submarine melt) and surface mass balance of the ice cap of Livingston Island, the second largest island in the South Shetland Islands archipelago, and analyse variations in surface velocity for the period 2007-2011. Velocities are obtained from feature tracking using 25 PALSAR-1 images, and used in conjunction with estimates of glacier ice thicknesses inferred from principles of glacier dynamics and ground-penetrating radar observations to estimate frontal ablation rates by a flux-gate approach. Glacier-wide surface mass-balance rates are approximated from in situ observations on two glaciers of the ice cap. Within the limitations of the large uncertainties mostly due to unknown ice thicknesses at the flux gates, we find that frontal ablation (-509 +/- 263 Mt yr(-1), equivalent to -0.73 +/- 0.38 m w.e. yr(-1) over the ice cap area of 697 km(2)) and surface ablation (- 0.73 +/- 0.10 m w.e. yr(-1)) contribute similar shares to total ablation (-1.46 +/- 0.39 m w. e. yr(-1)). Total mass change ( delta M = - 0.67 +/- 0.40 m w.e. yr(-1)) is negative despite a slightly positive surface mass balance (0.06 +/- 0.14 m w .e. yr(-1)). We find large interannual and, for some basins, pronounced seasonal variations in surface velocities at the flux gates, with higher velocities in summer than in winter. Associated variations in frontal ablation ( of similar to 237 Mt yr(-1); -0.34 m w.e. yr(-1)) highlight the importance of taking into account the seasonality in ice velocities when computing frontal ablation with a flux-gate approach.
|
|
| 41. |
- Ostby, Torbjorn I., et al.
(author)
-
Parameter uncertainty, refreezing and surface energy balance modelling at Austfonna ice cap, Svalbard, 2004-08
- 2013
-
In: Annals of Glaciology. - 0260-3055 .- 1727-5644. ; 54:63, s. 229-240
-
Journal article (peer-reviewed)abstract
- We apply a physically based coupled surface energy balance and snowpack model to a site close to the equilibrium line on Austfonna ice cap, Svalbard, over the 2004-08 melt seasons, to explain contributions to the energy available for melting and to quantify the significance of refreezing. The model is forced using in situ meteorological measurements and precipitation downscaled from ERA-Interim reanalysis. Applying a Monte Carlo approach to determine the tunable parameters of the model, we estimate the uncertainty related to the choice of parameter values. Multiple criteria are evaluated to identify well-performing parameter combinations, evaluating the model performance with respect to longwave outgoing radiation, snow and ice temperatures and surface displacement. On average, over the investigated melt seasons (1 June to 15 September) net radiation and sensible heat contributed 90 +/- 2% and 10 +/- 2%, respectively, to the mean energy available for melting snow and ice. The energy consumed by subsurface heat exchange reduced runoff by 15 +/- 2% in 2004 and 49 +/- 3% in 2008. Refreezing of meltwater and rain was estimated to be 0.37 +/- 0.04 m w.e. a(-1) on average over the five seasons, which represents a considerable reduction of mass loss during summer. Our findings suggest that refreezing potentially exerts a decisive control on glacier mass balance in persistently snow- or firn-covered areas.
|
|
| 42. |
- Pettersson, Rickard, 1972-
(author)
-
Dynamics of the cold surface layer of polythermal Storglaciären, Sweden
- 2004
-
Doctoral thesis (other academic/artistic)abstract
- Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing.A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates.The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären.Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.
|
|
| 43. |
- Pfeffer, W. Tad, et al.
(author)
-
The Randolph Glacier Inventory : a globally complete inventory of glaciers
- 2014
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:221, s. 537-552
-
Journal article (peer-reviewed)abstract
- The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the similar to 198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999-2010 provided most of the outlines. Their total extent is estimated as 726 800 +/- 34 000 km(2). The uncertainty, about +/- 5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.
|
|
| 44. |
- Radic, Valentina, et al.
(author)
-
Analysis of scaling methods in deriving future volume evolutions of valley glaciers
- 2008
-
In: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:187, s. 601-612
-
Journal article (peer-reviewed)abstract
- Volume-area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea-level rise. We analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one-dimensional ice-flow model. The model is calibrated for six glaciers (Nigardsbreen, Rhonegletscher, South Cascade Glacier, Sofiyskiy glacier, midre Lovenbreen and Abramov glacier). Volume evolutions forced by different hypothetical mass-balance perturbations are compared with those obtained from volume-area (V-A), volume-length (V-L) and volume-area-length (V-A-L) scaling. Results show that the scaling methods mostly underestimate the volume losses predicted by the ice-flow model, up to 47% for V-A scaling and up to 18% for V-L scaling by the end of the 100 year simulation period. In general, V-L scaling produces closer simulations of volume evolutions derived from the ice-flow model, suggesting that V-L scaling may be a better approach for deriving volume projections than V-A scaling. Sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants, yielding both over- and underestimates. However, when normalized by initial volume, volume evolutions are relatively insensitive to the choice of scaling constants, especially in the V-L scaling. The 100 year volume projections differ within 10% of initial volume when the V-A scaling exponent commonly assumed, gamma = 1.375, is varied by -30% to +45% (gamma = [0.95, 2.00]) and the V-L scaling exponent, q = 2.2, is varied by -30% to +45% (q = [1.52, 3.20]). This is encouraging for the use of scaling methods in glacier volume projections, particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown.
|
|
| 45. |
- Radic, Valentina, et al.
(author)
-
Glaciers in The Earth’s Hydrological Cycle : Assessments of Glacier Mass and Runoff Changes on Global and Regional Scales
- 2014
-
In: Surveys in geophysics. - 0169-3298 .- 1573-0956. ; 35:3, s. 813-837
-
Journal article (peer-reviewed)abstract
- Changes in mass contained by mountain glaciers and ice caps can modify theEarth’s hydrological cycle on multiple scales. On a global scale, the mass loss fromglaciers contributes to sea-level rise. On regional and local scales, glacier meltwater is animportant contributor to and modulator of river flow. In light of strongly acceleratedworldwide glacier retreat, the associated glacier mass losses raise concerns over the sus-tainability of water supplies in many parts of the world. Here, we review recent attempts toquantify glacier mass changes and their effect on river runoff on regional and global scales.We find that glacier runoff is defined ambiguously in the literature, hampering directcomparison of findings on the importance of glacier contribution to runoff. Despite con-sensus on the hydrological implications to be expected from projected future warming,there is a pressing need for quantifying the associated regional-scale changes in glacierrunoff and responses in different climate regimes.
|
|
| 46. |
- Radic, Valentina, et al.
(author)
-
Modeling future glacier mass balance and volume changes using ERA-40 reanalysis and climate models: A sensitivity study at Storglaciären, Sweden
- 2006
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:F03003
-
Journal article (peer-reviewed)abstract
- Modeling the response of glaciers to future climate change is important for predicting changes in global sea level rise and local water resources. We compute until the year 2100 the mass balance and volume evolution of Storglacia¨ren, a small valley glacier in Sweden, using a temperature index mass balance model. We focus on the sensitivity of results to the choice of climate model and variants of adjusting ERA-40 temperatures to local conditions. ERA-40 temperature and precipitation series from 1961 to 2001 are validated and used both as input to the mass balance model and for statistical downscaling of one regional and six global climate models (GCMs). Future volume projections are computed using area-volume scaling and constant glacier area. ERA-40 data correlate well with observations and capture observed interannual variability of temperature and precipitation. The mass balance model driven by several variants of ERA-40 input performs similarly well regardless of temporal resolution of the input series (daily or monthly). The model explains _70% of variance of measured mass balance when the input temperatures are reduced by the lapse rate that maximizes model performance. Fitting ERA-40 temperatures to observations close to the glacier does not improve the performance of the model, leading us to conclude that ERA-40 can be used for mass balance modeling independent of meteorological observations. Projected future volume series show a loss of 50–90% of the initial volume by 2100. The differences in volume projections vary by 40% of the initial volume for six different GCMs input to mass balance model, while each volume projection varies by 20% depending on whether volume-area scaling or constant area is used and by 10% depending on details in the mass balance model used. The correction of biases in the seasonal temperature cycle of the GCMs with respect to the ERA-40 data is crucial for deriving realistic volume evolution. Static mass balance sensitivities to temperature and precipitation change in the 21st century are -0.48 m yr_1 K_1 and 0.025 m yr_1 per % increase, respectively.
|
|
| 47. |
- Radic, V, et al.
(author)
-
Regional and global projections of 21st century glacier mass changes in response to climate scenarios from global climate models.
- 2013
-
In: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 42:1-2, s. 37-58
-
Journal article (peer-reviewed)abstract
- A large component of present-day sea-level rise is due to the melt of glaciers other than the ice sheets. Recent projections of their contribution to global sea-level rise for the twenty-first century range between 70 and 180 mm, but bear significant uncertainty due to poor glacier inventory and lack of hypsometric data. Here, we aim to update the projections and improve quantification of their uncertainties by using a recently released global inventory containing outlines of almost every glacier in the world. We model volume change for each glacier in response to transient spatially-differentiated temperature and precipitation projections from 14 global climate models with two emission scenarios (RCP4.5 and RCP8.5) prepared for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The multi-model mean suggests sea-level rise of 155 ± 41 mm (RCP4.5) and 216 ± 44 mm (RCP8.5) over the period 2006–2100, reducing the current global glacier volume by 29 or 41 %. The largest contributors to projected global volume loss are the glaciers in the Canadian and Russian Arctic, Alaska, and glaciers peripheral to the Antarctic and Greenland ice sheets. Although small contributors to global volume loss, glaciers in Central Europe, low-latitude South America, Caucasus, North Asia, and Western Canada and US are projected to lose more than 80 % of their volume by 2100. However, large uncertainties in the projections remain due to the choice of global climate model and emission scenario. With a series of sensitivity tests we quantify additional uncertainties due to the calibration of our model with sparsely observed glacier mass changes. This gives an upper bound for the uncertainty range of ±84 mm sea-level rise by 2100 for each projection.
|
|
| 48. |
- Radic, Valentina, et al.
(author)
-
Regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data
- 2010
-
In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:1, s. F01010-
-
Journal article (peer-reviewed)abstract
- Very few global-scale ice volume estimates are available for mountain glaciers and ice caps, although such estimates are crucial for any attempts to project their contribution to sea level rise in the future. We present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from similar to 123,000 glaciers from a recently extended World Glacier Inventory. We compute glacier volumes and their sea level equivalent (SLE) for 19 glacierized regions containing all mountain glaciers and ice caps on Earth. On the basis of total glacierized area of 741 x 10(3) +/- 68 x 10(3) km(2), we estimate a total ice volume of 241 x 10(3) +/- 29 x 10(3) km(3), corresponding to 0.60 +/- 0.07 m SLE, of which 32% is due to glaciers in Greenland and Antarctica apart from the ice sheets. However, our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried, i.e., Antarctica, North America, Greenland, and Patagonia. This emphasizes the need for more volume observations, especially of large glaciers and a more complete World Glacier Inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps.
|
|
| 49. |
- Radic, Valentina, et al.
(author)
-
Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise
- 2011
-
In: Nature Geoscience. - : Springer Nature. - 1752-0894 .- 1752-0908. ; 4:2, s. 91-94
-
Journal article (peer-reviewed)abstract
- The contribution to sea-level rise from mountain glaciers and ice caps has grown over the past decades. They are expected to remain an important component of eustatic sea-level rise for at least another century(1,2), despite indications of accelerated wastage of the ice sheets(3-5). However, it is difficult to project the future contribution of these small-scale glaciers to sea-level rise on a global scale. Here, we project their volume changes due to melt in response to transient, spatially differentiated twenty-first century projections of temperature and precipitation from ten global climate models. We conduct the simulations directly on the more than 120,000 glaciers now available in the World Glacier Inventory(6), and upscale the changes to 19 regions that contain all mountain glaciers and ice caps in the world (excluding the Greenland and Antarctic ice sheets). According to our multi-model mean, sea-level rise from glacier wastage by 2100 will amount to 0.124 +/- 0.037 m, with the largest contribution from glaciers in Arctic Canada, Alaska and Antarctica. Total glacier volume will be reduced by 21 +/- 6%, but some regions are projected to lose up to 75% of their present ice volume. Ice losses on such a scale may have substantial impacts on regional hydrology and water availability(7).
|
|
| 50. |
- Radic, Valentina, et al.
(author)
-
Volume-area scaling vs flowline modelling in glacier volume projections
- 2007
-
In: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 46:1, s. 234-240
-
Journal article (peer-reviewed)abstract
- Volume-area scaling provides a practical alternative to ice-flow modelling to account for glacier size changes when modelling future glacier evolutions, however, uncertainties remain as to the validity of the approach under non-steady conditions. We address these uncertainties by deriving scaling exponents in volume-area relationship from one-dimensional ice-flow modelling. We generate a set of 37 synthetic steady-state glaciers of different sizes, and then model volume evolutions due to climate warming and cooling as prescribed by negative and positive mass balance perturbations, respectively, on a century time scale. The scaling exponent derived for the steady-state glaciers (=1.56) differs from the exponents derived from the glaciers in transient (non-steady) state by up to 86%. Nevertheless, volume projections employing volume-area scaling are relatively insensitive to these differences in scaling exponents. Volume-area scaling agrees well with the results from ice-flow modelling and is able to simulate the approach of a glacier to a new steady state, if mass-balance elevation feedback is considered by adding or removing elevation bands at the lowest part of the glacier in response to mass balance variations. Provided area-changes are considered in the mass balance computations in this way, our results indicate that volume-area scaling is a powerful tool for glacier volume projections on multi-century time scales.
|
|
