Andreas Linsbauer

Modeling of glacier bed topography from glacier outlines, central branch lines, and a DEM

Due to the expected future climate change, glacier ice as a resource will be further diminished and its sea-level rise contribution further increased. A key for a more accurate determination of future glacier evolution is to improve our currently sparse knowledge on glacier bedrock topography. Here, we present a simplified method implemented in a geographic information system to approximate subglacial topography at a regional scale from spatial interpolation of local ice thickness values. The latter were derived from an ice-dynamical approach, which relates glacier thickness to its local surface slope, total vertical extent, and basal shear stress. The only input data required are glacier outlines, a set of central branch lines, and a digital elevation model (DEM). The modeled glacier beds are in good agreement with other, more complex modeling approaches and direct measurements. The observed local deviations can be explained with the sensitive dependence of our approach on the surface slope and the different methods used for spatial interpolation. The mean glacier thickness derived here for a sample of 40 glaciers in the Swiss Alps is slightly smaller than that derived from a similar, but scalar approach. Further adjustments of the data processing are possible to achieve agreement with available validation data. However, despite its local inaccuracies, the resulting DEM without glaciers can facilitate several applications such as the detection of overdeepenings or the modeling of future glacier evolution.

Modelling glacier-bed overdeepenings and possible future lakes for the glaciers in the Himalaya—Karakoram region

Abstract Surface digital elevation models (DEMs) and slope-related estimates of glacier thickness enable modelling of glacier-bed topographies over large ice-covered areas. Due to the erosive power of glaciers, such bed topographies can contain numerous overdeepenings, which when exposed following glacier retreat may fill with water and form new lakes. In this study, the bed overdeepenings for ~28 000 glaciers (40 775 km2) of the Himalaya-Karakoram region are modelled using GlabTop2 (Glacier Bed Topography model version 2), in which ice thickness is inferred from surface slope by parameterizing basal shear stress as a function of elevation range for each glacier. The modelled ice thicknesses are uncertain (±30%), but spatial patterns of ice thickness and bed elevation primarily depend on surface slopes as derived from the DEM and, hence, are more robust. About 16 000 overdeepenings larger than 104m2 were detected in the modelled glacier beds, covering an area of ~2200 km2 and having a volume of ~120km3 (3-4% of present-day glacier volume). About 5000 of these overdeepenings (1800 km2) have a volume larger than 106m3. The results presented here are useful for anticipating landscape evolution and potential future lake formation with associated opportunities (tourism, hydropower) and risks (lake outbursts).

Comparing three different methods to model scenarios of future glacier change in the Swiss Alps

Abstract Ongoing atmospheric warming causes rapid shrinking of glaciers in the European Alps, with a high chance of their near-complete disappearance by the end of the 21st century. Here we present a comparison of three independent approaches to model the possible evolution of the glaciers in the Swiss Alps over the 21st century. The models have different levels of complexity, work at a regional scale and are forced with three scenarios of temperature increase (low, moderate, high). The moderate climate scenario gives an increase in air temperature of ∼2°C and ∼4°C for the two scenario periods 2021-50 and 2070-99, respectively, resulting in an area loss of 60-80% by 2100. In reality, the shrinkage could be even faster, as the observed mean annual thickness loss is already stronger than the modelled one. The three approaches lead to rather similar results with respect to the overall long-term evolution. The choice of climate scenarios produces the largest spread (∼40%) in the final area loss, while the uncertainty in present-day ice-thickness estimation causes about half this spread.

The Swiss Alpine glaciers' response to the global '2 C air temperature target'

While there is general consensus that observed global mean air temperature has increased during the past few decades and will very likely continue to rise in the coming decades, the assessment of the effective impacts of increased global mean air temperature on a specific regional-scale system remains highly challenging. This study takes up the widely discussed concept of limiting global mean temperature to a certain target value, like the so-called 2 °C target, to assess the related impacts on the Swiss Alpine glaciers. A model setup is introduced that uses and combines homogenized long-term meteorological observations and three ensembles of transient gridded Regional Climate Model simulations to drive a distributed glacier mass balance model under a (regionalized) global 2 °C target scenario. 101 glaciers are analyzed representing about 50% of the glacierized area and 75% of the ice volume in Switzerland. In our study, the warming over Switzerland, which corresponds to the global 2 °C target is met around 2030, 2045 and 2055 (depending on the ensemble) for Switzerland, and all glaciers have fully adjusted to the new climate conditions at around 2150. By this time and relative to the year 2000, the glacierized area and volume are both decreased to about 35% and 20%, respectively, and glacier-based runoff is reduced by about 70%.

Glacial lake outburst flood risk in Himachal Pradesh, India: an integrative and anticipatory approach considering current and future threats

Glacial lake outburst floods (GLOFs) are a serious and potentially increasing threat to livelihoods and infrastructure in most high-mountain regions of the world. Here, we integrate modelling approaches that capture both current and future potential for GLOF triggering, quantification of affected downstream areas, and assessment of the underlying societal vulnerability to such climate-related disasters, to implement a first-order assessment of GLOF risk across the Himalayan state of Himachal Pradesh (HP), Northern India. The assessment thereby considers both current glacial lakes and modelled future lakes that are expected to form as glaciers retreat. Current hazard, vulnerability, and exposure indices are combined to reveal several risk ‘hotspots’, illustrating that significant GLOF risk may in some instances occur far downstream from the glaciated headwaters where the threats originate. In particular, trans-national GLOFs originating in the upper Satluj River Basin (China) are a threat to downstream areas of eastern HP. For the future deglaciated scenario, a significant increase in GLOF hazard levels is projected across most administrative units, as lakes expand or form closer towards steep headwalls from which impacts of falling ice and rock may trigger outburst events. For example, in the central area of Kullu, a 7-fold increase in the probability of GLOF triggering and a 3-fold increase in the downstream area affected by potential GLOF paths can be anticipated, leading to an overall increase in the assigned GLOF hazard level from ‘high’ to ‘very high’. In such instances, strengthening resilience and capacities to reduce the current GLOF risk will provide an important first step towards adapting to future challenges.

Mass Balance Re-analysis of Findelengletscher, Switzerland; Benefits of Extensive Snow Accumulation Measurements

A re-analysis is presented here of a 10-year mass balance series at Findelengletscher, a temperate mountain glacier in Switzerland. Calculating glacier-wide mass balance from the set of glaciological point balance observations using conventional approaches, such as the profile or contour method, resulted in significant deviations from the reference value given by the geodetic mass change over a five-year period. This is attributed to the sparsity of observations at high elevations and to the inability of the evaluation schemes to adequately estimate accumulation in unmeasured areas. However, measurements of winter mass balance were available for large parts of the study period from snow probings and density pits. Complementary surveys by helicopter-borne ground-penetrating radar (GPR) were conducted in three consecutive years. The complete set of seasonal observations was assimilated using a distributed mass balance model. This model-based extrapolation revealed a substantial mass loss at Findelengletscher of -0.43m w.e. a^-1 between 2004 and 2014, while the loss was less pronounced for its former tributary, Adlergletscher (-0.30m w.e. a^-1). For both glaciers, the resulting time series were within the uncertainty bounds of the geodetic mass change. We show that the model benefited strongly from the ability to integrate seasonal observations. If no winter mass balance measurements were available and snow cover was represented by a linear precipitation gradient, the geodetic mass balance was not matched. If winter balance measurements by snow probings and snow density pits were taken into account, the model performance was substantially improved but still showed a significant bias relative to the geodetic mass change. Thus the excellent agreement of the model-based extrapolation with the geodetic mass change was owed to an adequate representation of winter accumulation distribution by means of extensive GPR measurements.

Current and Future Glacial Lake Outburst Flood Hazard: Application of GIS-Based Modeling in Himachal Pradesh, India

Most studies concerning the hazard from glacial lake outburst floods have focused on the threat from lakes that have formed over the past century, some of which have demonstrated significant growth in response to recent warming of the climate system. However, attention is shifting toward the anticipation of future hazard and risk associated with new lakes that will develop as glaciers continue to retreat and water accumulates within depressions in the exposed bed topography. Using the Indian Himalayan state of Himachal Pradesh as a case study, this chapter provides both a review and implementation of modern approaches to assess current and future glacier lake outburst flood hazard over large spatial scales. Across Himachal Pradesh, the formation of new lakes over the next decades will lead to a minimum two- to threefold increase in land area affected by potential lake outburst floods in several districts. Generally the potential increase in glacial lake outburst flood frequency is demonstrated to be even greater, owing to the heightened opportunity for ice or rock avalanches to impact into larger and more numerous glacial lakes. Methods described herein allow early anticipation of future threats, providing a scientific basis for sound adaptation and planning responses.