Glacier Altitude Research Articles

The surface of small glaciers as radioactive hotspots: Concentration of radioisotopes during predicted intensive melting in the Alps

Glaciers are considered secondary sources of pollutants, including radioisotopes such as Cesium or Plutonium, with heightened concentrations compared to other ecosystems. The predicted melting of glaciers poses a substantial risk of releasing stored radioisotopes, yet understanding the glacier-specific factors influencing their concentration remains limited. This study investigates the relationship between glacier altitude, surface area, organic matter content in dark supraglacial sediment (cryoconite), precipitation, and activity concentrations of natural (210Pb) and anthropogenic radionuclides (137Cs and 241Am) across 19 Alpine glaciers. Results indicate that radioisotope concentrations depend on organic matter content in the cryoconite, highlighting the role of biotic-abiotic interactions in pollutant accumulation on glaciers. Moreover, 210Pb activity concentration decreases with glacier altitude, likely due to atmospheric variations in 222Rn. Water precipitation events, such as during peaks in 137Cs deposition and after the Chernobyl Nuclear Power Plant disaster, do not impact current activity concentrations. Importantly, radioisotope concentrations in cryoconite are higher on smaller glaciers. This directly supports the hypothesis that the cryoconite retains a significant share of radioisotopes stored in the ice during intensive melting. Since many small glaciers in the Alps are predicted to disappear within the next 50 years, we anticipate release of radioisotopes to mountain ecosystems might be higher than previously forecasted.

Geomorphological record and equilibrium line altitude of glaciers during the last glacial maximum in the Rodna Mountains (eastern Carpathians) – Corrigendum

Geomorphological record and equilibrium line altitude of glaciers during the last glacial maximum in the Rodna Mountains (eastern Carpathians) – Corrigendum

Monitoring the Spatiotemporal Difference in Glacier Elevation on Bogda Mountain from 2000 to 2017.

The difference in glacier surface elevation is a sensitive indicator of climate change and is also important for disaster warning and water supply. In this paper, 25 glaciers on Bogda Mountain, in the eastern Tianshan Mountains, are selected as the study object as they are typical of glaciers in arid or semi-arid areas with importance for water supply. The Repeat Orbit Interferometry (ROI) method is used to survey the surface elevation of these glaciers using Sentinel-1A Radar data from 2017. Using data from the Shuttle Radar Topography Mission (SRTM) and a Digital Elevation Model (DEM), the difference in the glacier surface elevation between 2000 and 2017 is obtained. A scheme to evaluate the accuracy of estimated variations in glacier surface elevation is proposed in this article. By considering the surfaces of lakes in the study region as ideal horizontal planes, the average standard deviation (SD) value of the lake elevation is taken as the error caused by the radar sensor and observing conditions. The SD of the lake elevation is used as an index to evaluate the error in the estimated variation of the glacier surface elevation, and the obtained SD values indicate that the result obtained using the ROI method is reliable. Additionally, the glacier surface elevation variation pattern and a Logarithmic Fitting Model (LFM) are used to reduce the error in high-altitude glacial accumulation areas to improve the estimation of the difference in the glacier surface elevation obtained using ROI. The average SD of the elevation of the 12 lakes is ±2.87 m, which shows that the obtained glacier surface elevations are reliable. This article concludes that, between 2000 and 2017, the surface elevation of glaciers on Bogda Mountain decreased by an average of 11.6 ± 1.3 m, corresponding to an average decrease rate of 0.68 m/a, and glaciers volume decreased by an average of 0.504 km3. Meanwhile, the surface elevations of the lakes increased by an average of 8.16 m. The decrease of glacier surface elevation leads to the expansion of glacial lakes. From the north slope clockwise to the south slope, the glacier elevation variation showed a decreasing trend, and the elevation variation gradually increased from the south slope to the north slope. With the increase of glacier altitude, the variation of glacier surface elevation gradually changed from negative to positive. The findings of this article suggest that the rate of glacier retreat on Bogda Mountain increased from 2000 to 2017.

Geomorphological record and equilibrium line altitude of glaciers during the last glacial maximum in the Rodna Mountains (eastern Carpathians)

AbstractIn the eastern Carpathians the legacy of glaciation is preserved in several isolated mountain massifs. This paper presents new mapping results of glaciated valley land systems in the Rodna Mountains, the highest part of the eastern Carpathians (2303 m above seal level). In most of the glacial valleys, the maximal Pleistocene extent is marked by freshly shaped moraines, which are referred in this study as the Pietroasa glacial stage and regarded as the last glacial maximum (LGM) advance. Only in three valleys do older Şesura glacial stage moraines (pre-LGM, likely Marine Oxygen Isotope Stage 6) occur. On the basis of the geomorphological record, we reconstruct the extent, surface geometry, and equilibrium line altitude (ELA) of Pietroasa-stage glaciers. The local ELA pattern of north-exposed glaciers in the Rodna Mountains shows a rising trend towards the southeast, which suggests dominant snow-bearing winds and orographically induced precipitation from the west. This finding fits well with the dominant palaeo-wind direction inferred from other Carpathian proxies and confirms the dominance of zonal circulation pattern during the global LGM in central eastern Europe.

A glacial buzzsaw effect generated by efficient erosion of temperate glaciers in a steady state model

Studies on relief and hypsometry in glaciated mountain ranges have recognized the equilibrium line altitude of glaciers as a major control on mountain height. This has led to the belief that, in contrast to fluvial topography, glacial topography is limited by climate, with tectonics playing a secondary role. This concept is known as the glacial buzzsaw. However, the understanding of controls on glacial relief has remained mainly qualitative, in part because a reference scenario for glacial landscape evolution — a glacial topographic steady state linked to the base level by a fluvial topographic steady-state downstream of the glacier terminus - and its dependencies have not yet been defined. Here we define such a reference and compare steady state longitudinal profiles in a coupled system of glacial and fluvial erosion that involves both tectonics and climate. Our model is based on the stream power law for fluvial erosion, the shallow ice approximation in combination with a glacial erosion rule, and an empirically determined drainage area-flow length relationship for both rivers and glaciers. Further, we introduce a new approach to incorporate dendritic glacier network structures into the one-dimensional model. Modeling of coupled glacial-fluvial steady-state profiles with empirical glacial and fluvial erosion parameters shows that the difference between glacial and fluvial relief depends on climate, tectonics and the applied erosion laws. Our results imply that glacial erosion can typically balance tectonic uplift rates at lower relief and topographic slopes than fluvial erosion. This steady state equivalent of the glacial buzzsaw effect suggests that glaciers may indeed be more efficient erosional agents than rivers increasing erosion in a cooling climate.

Long-term mass balance modelling (1986–2018) and climate sensitivity of Siachen Glacier, East Karakoram

Located in the eastern lap of the Karakoram Range, the Siachen Glacier is the second longest glacier in the non-polar areas of the world. High altitude, extreme climate and frequent military conflicts on this glacier create antagonistic surroundings for conventional field studies. Although recent advancements in geodetic technique have helped in the estimation of Siachen mass budget (MB), these geodetic estimates have been observed only for short time periods ranging 6 to 10years. Hence, current study presents a comprehensive assessment of the Siachen long-term MB (32 years) based on temperature index(TI) model. Annual surface MB variability was modelled between 1986 and 2018 by forcing daily air temperature and precipitation from multiple ground stations distributed well across accumulation/ablation zone of the glacier. Mean annual temperature lapse rate (LR) was found midway between dry adiabatic and moist adiabatic LRs. Precipitation gradient (PG) was observed remarkably different below and above 4800m.a.s.l. glacier altitude. Furthermore, snowmelt factor (SMF) was also estimated using snow thickness and positive degree days (PDDs) information over the glacier surface. Model results showed a nearly balanced condition (- 0.02 ± 0.05m.w.e./year) during 1986-2006 followed by anaccelerated rate of mass loss during 2007-2018 (- 0.11 ± 0.05m.w.e./year), thus making the overall condition of Siachen MB negative during the period 1986-2018 (- 0.05 ± 0.05m.w.e./year). Comparison of modelled MB was made with few geodetic studies conducted for the Siachen Glacier at different time scales (mainly after year 2000). Further, the sensitivity of the modelled glacier-wide MB was - 0.24m.w.e./year for a temperature rise by 1°C, while the sensitivity towards 10% increasein precipitation was estimated to be + 0.16m.w.e./year. A relationship of the annual MB with accumulation area ratio (AAR) and equilibrium line altitude (ELA) was also established for Siachen glacier.

Multi-Criteria Evaluation of Snowpack Simulations in Complex Alpine Terrain Using Satellite and In Situ Observations

This work presents an extensive evaluation of the Crocus snowpack model over a rugged and highly glacierized mountain catchment (Arve valley, Western Alps, France) from 1989 to 2015. The simulations were compared and evaluated using in-situ point snow depth measurements, in-situ seasonal and annual glacier surface mass balance, snow covered area evolution based on optical satellite imagery at 250 m resolution (MODIS sensor), and the annual equilibrium-line altitude of glaciers, derived from satellite images (Landsat, SPOT, and ASTER). The snowpack simulations were obtained using the Crocus snowpack model driven by the same, originally semi-distributed, meteorological forcing (SAFRAN) reanalysis using the native semi-distributed configuration, but also a fully distributed configuration. The semi-distributed approach addresses land surface simulations for discrete topographic classes characterized by elevation range, aspect, and slope. The distributed approach operates on a 250-m grid, enabling inclusion of terrain shadowing effects, based on the same original meteorological dataset. Despite the fact that the two simulations use the same snowpack model, being potentially subjected to same potential deviation from the parametrization of certain physical processes, the results showed that both approaches accurately reproduced the snowpack distribution over the study period. Slightly (although statistically significantly) better results were obtained by using the distributed approach. The evaluation of the snow cover area with MODIS sensor has shown, on average, a reduction of the Root Mean Squared Error (RMSE) from 15.2% with the semi-distributed approach to 12.6% with the distributed one. Similarly, surface glacier mass balance RMSE decreased from 1.475 m of water equivalent (W.E.) for the semi-distributed simulation to 1.375 m W.E. for the distribution. The improvement, observed with a much higher computational time, does not justify the recommendation of this approach for all applications; however, for simulations that require a precise representation of snowpack distribution, the distributed approach is suggested.

Glacier variations in response to climate change in the eastern Nyainqêntanglha Range, Tibetan Plateau from 1999 to 2015

ABSTRACT Changes in glaciers in response to climate change in the eastern Nyainqêntanglha Range were studied using Landsat TM/ETM+/OLI. The entire mountain range contained approximately 6,426 glaciers, covering an area of 6508.03 ± 252.02 km2 in 1999. The glaciers shrank from 1999 to 2015 and the total ice cover was reduced by 1285.99 ± 6.01 km2, accounting for 19.76 ± 3.78% of the glacierized area in 1999. The mean loss of glacier area was 1.24%•a−1 during 1999–2015. The analysis of meteorological data showed a remarkable pattern in mean annual air temperature (especially after 1998), whereas the annual precipitation displayed a stable pattern from 1989 to 2011. The glacier shrinkage in the region can probably be attributed to the increase in air temperature. The largest glaciers in the area show a maximum elevation of about 5,200–5,400 m a.s.l. in 1990, 2013, and 2015. The altitude of glaciers varied from 4,000 m a.s.l. to 6,000 m a.s.l. and the majority of the glaciers were distributed between 4,800 m and 5,800 m. All glaciers, regardless of their orientation, have shrunk, but glaciers mainly south-facing retreated faster than those facing others directions.

Modelling of Meteorological Parameters for the Chorabari Glacier Valley, Central Himalaya, India

In the present study, we have developed empirical relationships to estimate meteorological parameters at the glacier altitude from the data on non-glacier altitude. Meteorological data collected from automatic weather station at Chorabari Glacier from November 2011 to May 2013 are analysed and empirical equations for air temperature, relative humidity and incoming global radiation are proposed. The dataset of one year (November 2011-October 2012) is used in the calibration of models, while data for the next seven months (November 2012-May 2013) are employed to validate the models. Moreover, an analytical study is also conducted on incoming diffuse radiation (estimated through the established model for India). Further, a relationship is established to correlate the diffuse component of two sites. Variation trend of meteorological parameters with altitude is found to be different for each of the parameters, viz. quadratic for air temperature, logarithmic for relative humidity, and linear for global and diffuse radiation. Performance of the generated equations is tested through various statistical methods. The study reveals that developed correlations are able to give a good match with in situ measurements.

Recent trends in annual snowline variations in the northern wet outer tropics: case studies from southern Cordillera Blanca, Peru

This paper describes the changes in the annual maximum snowlines of a selected set of mountain glaciers at the southern end of the Cordillera Blanca between 1984 and 2015 using satellite images. Furthermore, we analysed the existing glacier records in the Cordillera Blanca since the last glacial maximum to understand the evolution of glaciers in this region over a few centuries. There was a rise in the snowline altitude of glaciers in this region since the late 1990s with a few small glacier advances. Historical to the present El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) records were also analysed to understand whether there was a teleconnection between the glacier fluctuations in the region and the phase changes of ENSO and PDO. We also assessed the variations in three important climatic parameters that influence the glacier retreat—temperature, precipitation, and relative humidity—over a few decades. We calculated the anomalies as well as the seasonal changes in these variables since the mid-twentieth century. There was an increase in temperature during this period, and the decrease in precipitation was not so prominent compared with the temperature rise. There was an exceptionally higher increase in relative humidity since the early 2000s, which is relatively higher than that expected due to the observed rate of warming, and this increase in humidity is believed to be the reason behind the unprecedented rise in the snowline altitudes since the beginning of the twenty-first century.

New inventory of glaciers in southeastern part of the Eastern Sayan Mountains

Satellite images with high (Quick Bird, 2006, WorldView-1, 2008, 0.5–0.6 m) and middle (Landsat-7 ETM +, 2001, 15–30 m) resolution were used to map contemporary glaciers on two mountain peaks of south-eastern part of East Sayan Ridge – Munky Sardyk (3491 m a.s.l.) and Topographov (3089 m a.s.l.). Topographic maps of 1978 and 1981 and Landsat-7 images (summer 2001) were used to assess glacier changes during second half of XX century. Modern terminal and lateral moraines near glacier snouts were used to reconstruct former outlines during the end of the Little Ice Age (middle of XIX century). Also SRTM data and GPS-surveys in Munku-Sardyk area were applied to measure glacier altitudes. GIS technologies allowed forming digital glacier data base with attribute information and new inventory was made. Totally 13 glaciers with area of 5.1 km² were investigated and mapped. Glaciers are located in vertical range from 2800–3490 m a.s.l. (Munku-Sardyk area) and 2340–2950 m a.s.l. (Topographov area). Firn line on glaciers vary from 2540 to 3110 m a.s.l., rising to the southeast. On average, over the past 160 years (since the end of the Little Ice Age) glaciers have significantly decreased. Ice area has decreased by 49%, length has diminished by 570 m, the glacier snouts has risen by 124 m. Analysis of regional climate data shows that the rate of deglaciation is well correlated with summer temperatures increasing in the second half of XX century, especially in 1980–1990s. A tendency to recover glacier mass balance was revealed during the last decade based on climatic data.

Arctic Holocene proxy climate database – new approaches to assessing geochronological accuracy and encoding climate variables

Abstract. We present a systematic compilation of previously published Holocene proxy climate records from the Arctic. We identified 170 sites from north of 58° N latitude where proxy time series extend back at least to 6 cal ka (all ages in this article are in calendar years before present – BP), are resolved at submillennial scale (at least one value every 400 ± 200 years) and have age models constrained by at least one age every 3000 years. In addition to conventional metadata for each proxy record (location, proxy type, reference), we include two novel parameters that add functionality to the database. First, "climate interpretation" is a series of fields that logically describe the specific climate variable(s) represented by the proxy record. It encodes the proxy–climate relation reported by authors of the original studies into a structured format to facilitate comparison with climate model outputs. Second, "geochronology accuracy score" (chron score) is a numerical rating that reflects the overall accuracy of 14C-based age models from lake and marine sediments. Chron scores were calculated using the original author-reported 14C ages, which are included in this database. The database contains 320 records (some sites include multiple records) from six regions covering the circumpolar Arctic: Fennoscandia is the most densely sampled region (31% of the records), whereas only five records from the Russian Arctic met the criteria for inclusion. The database contains proxy records from lake sediment (60%), marine sediment (32%), glacier ice (5%), and other sources. Most (61%) reflect temperature (mainly summer warmth) and are primarily based on pollen, chironomid, or diatom assemblages. Many (15%) reflect some aspect of hydroclimate as inferred from changes in stable isotopes, pollen and diatom assemblages, humification index in peat, and changes in equilibrium-line altitude of glaciers. This comprehensive database can be used in future studies to investigate the spatio-temporal pattern of Arctic Holocene climate changes and their causes. The Arctic Holocene data set is available from NOAA Paleoclimatology.

Wind effects on snow cover in Pascua-Lama, Dry Andes of Chile

We present the first application of a distributed snow model (SnowModel) in the instrumented site of Pascua-Lama in the Dry Andes (2600–5630m above sea level, 29°S). A model experiment was performed to assess the effect of wind on the snow cover patterns. A particular objective was to evaluate the role of blowing snow on the glacier formation. The model was run using the data from 11 weather stations over a complete snow season. First, a cross-validation of the meteorological variables interpolation model (MicroMet submodel) was performed to evaluate the performance of the simulated meteorological forcing. Secondly, two SnowModel simulations were set up: one without and the other with the wind transport submodel (SnowTran-3D). Results from both simulations were compared with in situ snow depth measurements and remotely sensed snow cover data. The inclusion of SnowTran-3D does not change the fact that the model is unable to capture the small-scale snow depth spatial variability (as captured by in situ snow depth sensors). However, remote sensing data (MODIS daily snow product) indicate that at broader scales the wind module produced an improved representation of the snow distribution near the glaciers (2-D correlation coefficient increased from R=0.04 to R=0.27). The model outputs show that a key process is the sublimation of blowing snow, which amounts to 18% of the total ablation over the whole study area, with a high spatial variability. The effect of snow drift is more visible on the glaciers, where wind-transported snow accumulates preferentially. Net deposition occurred for 43% of the glacier grid points, whereas it is only 23% of non-glacier grid points located above the minimum glacier altitude (4475m).

Reconstructions of annual discharge and equilibrium line altitude of glaciers at Qilian Shan, northwest China, from 1978 to 2002

AbstractDischarge was calculated from a mountainous area, including discharge from glaciers, in the Qilian Shan (Qilian Mountains) of northwest China. The studied Yingluoxia basin is 9983 km2 in area, with glaciers making up 0·3% of the basin. The calculation method was based on the heat balance, requiring only daily temperature and precipitation. Calculated annual discharge from the basin corresponded well with the observed data. Calculated annual discharge from glaciers was 3·6% of the total discharge from the basin.The temporal trend of the calculated equilibrium line altitude (ELA) at the July 1st Glacier (western side of the Yingluoxia basin) was similar to that of the observed ELA. The calculated annual mass balance of glaciers within the Yingluoxia basin has a larger negative value than the other glaciers in China, as the ratio of accumulation area to the total glacier area in the Yingluoxia basin is much lower than in neighbouring basins to the west. Copyright © 2010 John Wiley & Sons, Ltd.

Glacier volume response time and its links to climate and topography based on a conceptual model of glacier hypsometry

Abstract. Glacier volume response time is a measure of the time taken for a glacier to adjust its geometry to a climate change. It has been previously proposed that the volume response time is given approximately by the ratio of glacier thickness to ablation at the glacier terminus. We propose a new conceptual model of glacier hypsometry (area-altitude relation) and derive the volume response time where climatic and topographic parameters are separated. The former is expressed by mass balance gradients which we derive from glacier-climate modelling and the latter are quantified with data from the World Glacier Inventory. Aside from the well-known scaling relation between glacier volume and area, we establish a new scaling relation between glacier altitude range and area, and evaluate it for seven regions. The presence of this scaling parameter in our response time formula accounts for the mass balance elevation feedback and leads to longer response times than given by the simple ratio of glacier thickness to ablation at the terminus. Volume response times range from decades to thousands of years for glaciers in maritime (wet-warm) and continental (dry-cold) climates respectively. The combined effect of volume-area and altitude-area scaling relations is such that volume response time can increase with glacier area (Axel Heiberg Island and Svalbard), hardly change (Northern Scandinavia, Southern Norway and the Alps) or even get smaller (The Caucasus and New Zealand).

Temperature and precipitation climate at the equilibrium-line altitude of glaciers expressed by the degree-day factor for melting snow

AbstractSeveral authors relate accumulation (or precipitation) at the glacier equilibrium-line altitude (ELA) to summer mean temperature using exponential or power-law functions. I analyze the accumulation–temperature relation at the ELA with a degree-day model using data from the 1992 paper by A. Ohmura and others. The dataset includes estimates at the ELA of winter balance and of ‘winter balance plus summer precipitation’ which represent respectively low and high estimates of annual accumulation, which is seldom measured. The Ohmura dataset only lists summer mean temperature, but I recover monthly temperatures for the whole year for 66 of the glaciers by assuming sinusoidal temperature variation through the year and using annual temperature range from a gridded climatology. Monthly degree-day sums are then estimated from monthly mean temperature and summed to give annual totals so degree-day factors for melting snow at the ELA are obtained. The degree-day factors fall close to those reported in the literature for glacier snowmelt, with averages of 3.5 ± 1.4 and 4.6 ± 1.4 mm d−1 K−1 for low- and high-accumulation estimates on the 66 glaciers. The degree-day model gives a family of accumulation–temperature curves that depend upon the annual temperature range, representing the contrast between maritime and continental climates.

An inventory and morphometric analysis of British Columbia glaciers, Canada

AbstractWe describe an automated method to generate an inventory of glaciers and glacier morphometry from a digital topographic database containing glacier boundaries and a digital elevation model for British Columbia, Canada. The inventory contains over 12 000 glaciers with a total cumulative area that exceeds 25 000 km2, based on mapping from aerial photographs circa the mid-1980s. We use the inventory to examine dimensional characteristics among glaciers, namely the scaling relations between glacier length, width and area. Glacier length is a good predictor of glacier area, and its predictive ability improves when glaciers are stratified by the number of up-valley accumulation basins. The spatial pattern of glacier mid-range altitude parallels glaciation limits previously mapped for British Columbia and similarly reflects large-scale controls of orographic precipitation and continentality. The inventory is also used to refine models that relate glacier mid-range and terminus altitudes to regional position, aspect and, in the case of terminus altitudes, an index of glacier shape. Relations between glacier altitude limits and controlling spatial and topographic factors are used to make further climatic and mass-balance inferences from the glacier inventory.

Distributed modelling of the regional climatic equilibrium line altitude of glaciers in the European Alps

Glaciers are among the key indicators of ongoing climate change. The equilibrium line altitude is a theoretical line which defines the altitude at which annual accumulation equals the ablation. It represents the lowest boundary of the climatic glacierisation and, therefore, is an excellent proxy for climate variability. In this study we introduce a simple approach for modelling the glacier distribution at high spatial resolution over entire mountain ranges using a minimum of input data. An empirical relationship between precipitation and temperature at the steady-state equilibrium line altitude (ELA 0), is derived from direct glaciological mass balance measurements. Using geographical information systems (GIS) and a digital elevation model, this relationship is then applied over a spatial domain, to a so-called distributed modelling of the regional climatic ELA 0 (rcELA 0) and the climatic accumulation area (cAA) of 1971–1990 over the entire European Alps. A sensitivity study shows that a change in rcELA 0 of ± 100 m is caused by a temperature change of ± 1 °C or a precipitation decrease of 20% and increase of 27%, respectively. The modelled cAA of 1971–1990 agrees well with glacier outlines from the 1973 Swiss Glacier Inventory. Assuming a warming of 0.6 °C between 1850 and 1971–1990 leads to a mean rcELA 0 rise of 75 m and a corresponding cAA reduction of 26%. A further rise in temperature of 3 °C accompanied by an increase in precipitation of 10% leads to a further mean rise of the rcELA 0 of about 340 m and reduces the cAA of 1971–1990 by 74%.

Glacier distribution in the alps: statistical modelling of altitude and aspect

Mass balance of glaciers in mountain areas varies not only with altitude and regional position but also with aspect, gradient, glacier size, glacier type and detailed topographic position. These factors are combined here in models of how glacier altitude varies, tested with data for the Alps edited from the World Glacier Inventory. An overall northward tendency in glacier numbers (toward 005 ± 4°) and lower altitudes (013 ± 5°) is maintained across a range of glacier sizes, types, altitudes and the major divisions of the Alps. Variation with aspect of glacier altitude (and, by implication, of glacier balance) in the Alps is essentially unimodal, and north‐facing glaciers average 220 m lower in middle altitude than south‐facing: 148 m in the Western Alps, 232 m in the West‐central, 252 m in the East‐central, and 268 m in the Eastern Alps. For smaller subdivisions, confidence intervals on estimates are broader and many differences lack statistical significance. Contrasts are greater in the higher massifs, with greater relief, and lower in cloudy, windward areas. There are small windrelated tendencies east of north along the northern and western fringes, but trends across space are weak: position is thus treated by subdivision into districts and groups. Mid‐altitude averages 2891 m overall and varies from 2552 to 3127 m for 27 glacier districts, and from 2124 to 3209 m for 103 glacier groups. Glacier mid‐altitude varies also with glacier form, nourishment, height range and area, which account for over two‐thirds of variance in combined models.

Accumulation at the equilibrium-line altitude of glaciers inferred from a degree-day model and tested against field observations

AbstractWe extrapolate temperature data from a gridded climatology to the equilibrium-line altitude (ELA) of a glacier and tune a degree-day model by adjusting precipitation to give zero mass balance at the ELA. We verify the tuned model by comparing modelled accumulation with winter balance where this has been measured (presently for 180 glaciers). The modelled accumulation naturally depends upon the vertical lapse rate (VLR) for temperature and the degree-day factor (DDF) for snowmelt. Both are somewhat uncertain in high-mountain areas, but modelled accumulation and measured winter balance are in reasonable agreement for most glaciers. The degree-day model predicts a non-linear relation between accumulation and summer temperature at the ELA as assumed by many workers, but we find a family of curves rather than a single universal curve. Maritime glaciers with low annual temperature range have proportionally more accumulation than continental glaciers with high annual temperature range for a similar summer mean temperature. Averages of winter balance for the five main geographical regions where mass-balance data are available agree well with annual accumulation from the degree-day model.