Air temperature is a key control of processes affecting snow and glaciers in high-elevation catchments, including melt, snowfall and sublimation. It is therefore a key input variable to models of land–surface–atmosphere interaction. Despite this importance, its spatial variability is poorly understood and simple assumptions are made to extrapolate it from point observations to the catchment scale. We use a dataset of 2.75 years of air temperature measurements (from May 2012 to November 2014) at a network of up to 27 locations in the Langtang River, Nepal, catchment to investigate air temperature seasonality and consistency between years. We use observations from high elevations and from the easternmost section of the basin to corroborate previous findings of shallow lapse rates. Seasonal variability is strong, with shallowest lapse rates during the monsoon season. Diurnal variability is also strong and should be taken into account since processes such as melt have a pronounced diurnal variability. Use of seasonal lapse rates seems crucial for glacio-hydrological modelling, but seasonal lapse rates seem stable over the 2–3 years investigated. Lateral variability at transects across valley is high and dominated by aspect, with south-facing sites being warmer than north-facing sites and deviations from the fitted lapse rates of up to several degrees. Local factors (e.g. topographic shading) can reduce or enhance this effect. The interplay of radiation, aspect and elevation should be further investigated with high-elevation transects.

We estimate all the individual glacier area and volume changes in High Mountain Asia (HMA) by 2050 based on Randolph Glacier Inventory (RGI) version 4.0, using different methods of assessing sensitivity to summer temperatures driven by a regional climate model and the IPCC A1B radiative forcing scenario. A large range of sea-level rise variation comes from varying equilibrium-line altitude (ELA) sensitivity to summer temperatures. This sensitivity and also the glacier mass-balance gradients with elevation have the largest coefficients of variability (amounting to ~50%) among factors examined. Prescribing ELA sensitivities from energy-balance models produces the highest sea-level rise (9.2 mm, or 0.76% of glacier volume a–1), while the ELA sensitivities estimated from summer temperatures at Chinese meteorological stations and also from 1°x1° gridded temperatures in the Berkeley Earth database produce 3.6 and 3.8 mm, respectively. Different choices of the initial ELA or summer precipitation lead to 15% uncertainties in modelled glacier volume loss. RGI version 4.0 produces 20% lower sea-level rise than version 2.0. More surface mass-balance observations, meteorological data from the glaciated areas, and detailed satellite altimetry data can provide better estimates of sea-level rise in the future.

Gravitational mass flows may generate tsunamis as they hit water bodies such as oceans, reservoirs or mountain lakes. Upon impact, they can generate tremendous particle-laden or debris flows and floods. Rapidly cascading waves down mountain slopes can trigger debris flows or floods, potentially causing huge damage to civil structures and endangering life. Here we apply a general two-phase mass flow model (Pudasaini, 2012), and present three-dimensional (3-D), high-resolution simulations for a real two-phase debris impacting a fluid reservoir. An innovative formulation provides an opportunity, within a single framework, to simulate simultaneously the sliding two-phase debris/landslide, reservoir, debris impact at reservoir, water-wave generation, propagation and mixing, and separation between solid and fluid phases. The results demonstrate formation and propagation of very special solid and fluid structures in the reservoir, propagation of submarine debris, turbidity currents, and complex interactions between the subaerial debris, surface tsunami and submarine debris waves. Our results reveal that the submerge timescaling for a deformable two-phase debris deviates substantially from the same for a non-deformable solid. These results substantially increase our understanding of 3-D complex multiphase systems/flows. This allows for the proper modeling of landslide/debris-induced mountain tsunami, dynamics of turbidity currents and highly concentrated sediment transports in Himalayan and Alpine slopes and channels, with associated applications to engineering, environmental and hazard-mitigation plans.

This study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area ~25km2) under the influence of climate change using multitemporal satellite imagery and local climate data. Between 1962 and 2013, Imja Lake expanded from 0.03±0.01 to 1.35±0.05 km2 at a rate of 0.026±0.001 km2 a-1. The mean glacier-wide flow velocity was 37±30ma-1 during 1992–93 and 23±15ma-1 during 2013–14, indicating a decreasing velocity. A mean elevation change of –1.29±0.71ma-1 was observed over the lower part of the glacier in the period 2001–14, with a rate of –1.06±0.63ma-1 in 2001–08 and –1.56±0.80ma-1 in 2008–14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions.

An ice core was extracted from the Zangser Kangri (ZK) ice field in the northern Tibetan Plateau (NTP), a location with limited instrumental and proxy records. In this paper, we present a continuous high–resolution dust concentration time series spanning the period AD 1951-2008 to investigate variations in atmospheric dust loading over the NTP. The results show that atmospheric dust loading exhibited significant decadal variations, with two periods of high dust loading (AD 1959–67 and AD 1979–89) and three periods of relatively low loading (AD 1951-58, AD 1968–78 and AD 1990–2008). The variability of atmospheric dust loading was related to wind speed at 500 hPa over the dust source regions. The winter Arctic Oscillation (AO) index showed a significant negative correlation with the annual dust concentration, implying a possible connection between the winter AO and the atmospheric dust loading over the NTP.

Two ice cores drilled to the bottom were recovered from Miaoergou flat-topped glacier (43°03'19“N, 94°19'21“E; 4512 ma.s.l.), eastern Tien Shan, central Asia, in 2005. A high–resolution record of cadmium was established by applying inductively coupled plasma mass spectrometry to one of the ice cores (57.6 m), covering a 228 year period from AD 1776 to 2004. The results showed long-term variations of atmospheric transport and deposition of cadmium at high altitudes. Trend analysis based on the sequential Mann-Kendall test and the analysis of crustal enrichment factors of the cadmium shows that natural contribution, mainly from rock and mineral dust, dominated the atmospheric cycles of cadmium during the period AD 1776–1957, which was confirmed by the significant correlation between the winter North Atlantic Oscillation (NAO) index and annual cadmium concentration. The concentration of cadmium increased sharply from AD 1957 to 2004, suggesting increasing influence from human activities, such as metals production. The ice–core record indicated increasing atmospheric cadmium pollution in response to rapid economic growth after AD 1957 in the region.

Snow cover and glaciers in the Karakoram region are important freshwater resources for many down-river communities as they provide water for irrigation and hydropower. A better understanding of current glacier changes is hence an important informational baseline. We present glacier elevation changes in the central Karakoram region using TanDEM-X and SRTM/X-SAR DEM differences between 2000 and 2012. We calculated elevation differences for glaciers with advancing and stable termini or surge-type glaciers separately using an inventory from a previous study. Glaciers with stable and advancing termini since the 1970s showed nearly balanced elevation changes of -0.09 ±0.12 m a-1 on average or mass budgets of -0.01 ±0.02Gt a-1 (using a density of 850 kg m-3). Our findings are in accordance with previous studies indicating stable or only slightly negative glacier mass balances during recent years in the Karakoram. The high-resolution elevation changes revealed distinct patterns of mass relocation at glacier surfaces during active surge cycles. The formation of kinematic waves at quiescent surge-type glaciers could be observed and points towards future active surge behaviour. Our study reveals the potential of the TanDEM-X mission to estimate geodetic glacier mass balances, but also points to still existing uncertainties induced by the geodetic method.

Correlations between a 1000 year record of the major ions in a 108.83 m ice core from East Rongbuk Glacier (28°01’N, 86°58’E; 6518ma.s.l.) on the northeast slope of Qomolangma (Mount Everest) and the Southern Oscillation Index (SOI) were examined to investigate possible links between the ice-core records of the southern Tibetan Plateau (TP) and El Niño Southern Oscillation (ENSO). The results show that years with the highest crustal ion concentrations and lowest marine ion concentrations corresponded with a low SOI, and vice versa. Cross wavelet and wavelet coherence analysis between major ion time series and the SOI indicated that there were significant sections with high common power between the major ion time series and the SOI, suggesting a correlation between the ion records of the Qomolangma ice core and ENSO. Further investigation indicated that the higher SOI years corresponded with weaker continental air masses and stronger south Asian monsoons over the southern TP, leading to increased marine ions and decreased continental ions transported to the southern TP. The in-phase surface pressure anomalies of the southern TP and Darwin, Australia, link ENSO and ion transport over the southern TP, and thus suggest a link between aerosol transport over the southern TP and ENSO.

This study presents the first decadal mass-balance record of a small debris-free glacier in the Bhutan Himalaya, where few in situ measurements have been reported to date. Since 2003 we have measured the mass balance of Gangju La glacier, which covers an area of 0.3km2 and extends from 4900 to 5200ma.s.l., using both differential GPS surveys (geodetic method) and stake measurements (direct method). The observed mass balance ranged from –1.12 to –2.04mw.e. a–1 between 2003 and 2014. The glacier exhibited much greater mass loss than neighbouring glaciers in the eastern Himalaya and southeastern Tibet, which are expected to be sensitive to climate change due to the monsooninfluenced humid climate. Observed mass-balance profiles suggest that the equilibrium-line altitude has been higher than Gangju La glacier since 2003, implying that the entire glacier has experienced net ablation for at least the past decade.

Estimates of melt from debris-covered glaciers require distributed estimates of meteorological variables and air temperature in particular. Meteorological data are scarce for this environment, and spatial variability of temperature over debris is poorly understood. Based on multiple measurements of air and surface temperature from three ablation seasons (2012–14) we investigate the variability of temperature over Lirung Glacier, Nepal, in order to reveal how air temperature is affected by the debris cover and improve ways to extrapolate it. We investigate how much on-glacier temperature deviates from that predicted from a valley lapse rate (LR), analyse on-glacier LRs and test regression models of air temperature and surface temperature. Air temperature over the debris-covered glacier tongue is much higher than what a valley LR would prescribe, so an extrapolation from off-glacier stations is not applicable. An on-glacier LR is clearly defined at night, with strong correlation, but not during the day, when the warming debris disrupts the elevation control. An alternative to derive daytime air temperature is to use a relationship between air and surface temperature, as previously suggested. We find strong variability during daytime that should be accounted for if these regressions are used for temperature extrapolation.

Glacier responses to future climate change will affect hydrology at sub-basin scales. The main goal of this study is to assess glaciological and hydrological sensitivities of sub-basins throughout the Hindu Kush-Himalaya region. We use a simple geometrical analysis based on a full glacier inventory and digital elevation model to estimate sub-basin equilibrium-line altitudes (ELAs) from assumptions of steady-state accumulation area ratios. The ELA response to an increase in temperature is expressed as a function of mean annual precipitation, derived from a range of high-altitude studies. Changes in glacier contributions to streamflow in response to increased temperatures are examined for scenarios of both static and adjusted glacier geometries. On average, glacier contributions to streamflow increase by ~50% for a +1 K warming based on a static geometry. Large decreases (-60% on average) occur in all basins when glacier geometries are instantaneously adjusted to reflect the new ELA. Finally, we provide estimates of sub-basin glacier response times that suggest a majority of basins will experience declining glacier contributions by 2100.

Radio-echo sounding techniques are very useful for fast profiling of seasonal snowpack. Ground-penetrating radar (GPR) is used widely for various cryospheric applications, such as snow/glacier depth estimation, snow layer identification and snow water equivalent assessment. The dielectric constant of snow is an important input parameter for the acquisition and interpretation of GPR data from the snowpack. In this study, snow dielectric constant was measured along with physical properties of snow using a snow fork operating at 1 GHz frequency. Experiments were conducted at field observatories of the Snow and Avalanche Study Establishment located in different Himalayan ranges: Patseo (Greater Himalayan range), Dhundhi and Solang (Pir Panjal range). Interseasonal spatial and temporal variations in snow dielectric constant and associated snowpack properties were analysed for five winter seasons (2010-14). The mean seasonal snow dielectric constant is higher at Dhundhi (1.82 ±0.02) than at Patseo (1.69 ±0.02). The measured snow dielectric constant was used to derive snow density and liquid-water content (LWC). A better correlation between snow dielectric constant and LWC is observed for high-density snow (>300kgm-3; R2 = 0.95) than for low-density snow (<200kgm-3; R2 = 0.73). Snow-fork-derived snow density was in good agreement with manually measured values. The snow dielectric constant database generated during this study can be used as a reference for various field applications of GPR in snow-related studies.

We present the updated glaciological mass balance (MB) of Chhota Shigri Glacier, the longest continuous annual MB record in the Hindu-Kush Karakoram Himalaya (HKH) region. Additionally, 4 years of seasonal MBs are presented and analyzed using the data acquired at an automatic weather station (AWS-M) installed in 2009 on a lateral moraine (4863ma.s.l.). The glaciological MB series since 2002 is first recalculated using an updated glacier hypsometry and then validated against geodetic MB derived from satellite stereo-imagery between 2005 (SPOT5) and 2014 (Pléiades). Chhota Shigri Glacier lost mass between 2002 and 2014 with a cumulative glaciological MB of –6.72mw.e. corresponding to a mean annual glacier-wide MB (Ba) of –0.56mw.e. a–1. Equilibrium-line altitude (ELA0) for the steady-state condition is calculated as ~4950ma.s.l., corresponding to an accumulation–area ratio (AAR0) of ~61%. Analysis of seasonal MBs between 2009 and 2013 with air temperature from AWS-M and precipitation from the nearest meteorological station at Bhuntar (1050ma.s.l.) suggests that the summer monsoon is the key season driving the interannual variability of Ba for this glacier. The intensity of summer snowfall events controls the Ba evolution via controlling summer glacier-wide MB (Bs).

Water stored as ice and snow at high elevations is a resource that plays an important role in the hydrologic cycle, particularly in the timing and volume of downstream discharge. Here we use geochemical and isotopic values of water samples to evaluate relative contributions of melting glacier ice and groundwater to discharge in Bhutan. River water samples were collected between 3100 and 4500 m in the Chamkar Chhu (river) watershed of central Bhutan's Himalaya. Glacier ice and snow were sampled in the ablation zone of Thanagang glacier. Groundwater was parameterized from spring water at elevations of 3100 and 3600 m. Synoptic sampling was carried out in separate expeditions in July, August and late September 2014, to characterize monsoon and post-monsoon conditions. Results from a two-component hydrologic mixing model using isotopic and geochemical (sulphate) values show that the glacier outflow contributions decrease from ∼76% at 4500 m to 31% at 3100 m. A four-component hydrologic mixing model using end-member mixing analysis shows glacier ice melt increasing as a proportion of discharge over the 3 month sampling period, and consistently decreasing with distance downstream of Thanagang glacier terminus. These results indicate that isotopic and geochemical tracers can provide a quantitative evaluation of the source water contributions to streamflow in Bhutan.

To simulate a glacial lake outburst flood, we employ a comprehensive physically based general two-phase mass flow model (Pudasaini, 2012). This model accounts for a strong interaction between the solid and fluid phases and incorporates buoyancy and other dominant physical aspects of the mass flows such as enhanced non-Newtonian viscous stress, virtual mass force and generalized drag. Our real two-phase mass flow simulation describes explicit evolution of the solid and fluid phases and the debris bulk as a whole, akin to torrential debris flows or debris floods during glacial lake outburst floods (GLOFs). The emptying of a lake following rapid collapse of a restraining dam, the consequent downslope motion of a mixed solid–fluid mass, and the tendency of the mass to form extruding plumes are analyzed in detail for different flow configurations, volumes, conduit geometries and boundary conditions. The solid and fluid phases evolve completely differently and reveal fundamentally different dynamical behaviours. During the flow, the relatively long fluid tail follows the solid-rich dense frontal surge head. The bulk debris develops into a frontal and side levee as derived from the initial frontal moraine dam. Results show that our high-resolution, unified simulation strategies and the advanced model equations can be applied to study the flow dynamics of a wide range of geophysical mass flows such as snow and rock–ice avalanches, debris flows and flash floods as well as GLOFs. This may help substantially in forming a basis for appropriate mitigation measures against potential natural hazards in high mountain slopes and valleys.

We use numerical modelling of glacier mass balance combined with recent and past glacier extents to obtain information on Little Ice Age (LIA) climate in southeastern Tibet. We choose two glaciers that have been analysed in a previous study of equilibrium-line altitudes (ELA) and LIA glacier advances with remote-sensing approaches. We apply a physically based surface energy- and mass-balance model that is forced by dynamically downscaled global analysis data. The model is applied to two glacier stages mapped from satellite imagery, modern (1999) and LIA. Precipitation scaling factors (PSF) and air temperature offsets (ATO) are applied to reproduce recent ELA and glacier mass balance (MB) during the LIA. A sensitivity analysis is performed by applying seasonally varying gradients of precipitation and air temperature. The calculated glacier-wide MB estimate for the period 2000–12 is negative for both glaciers (–992±366 kgm–2 a–1 and –1053±258 kgm–2 a–1). Relating recent and LIA PSF/ATO sets suggests a LIA climate with ~8–25% increased precipitation and ~1–2.5°C lower mean air temperature than in the period 2000–12. The results only provide an order of magnitude because deviations in other input parameters are not considered.

Photogrammetric measurements of powder-cloud surfaces from large avalanches enable the observation of cloud evolution and dispersion as well as quantification of cloud velocities and powder volumes. Since 2002, a total of six large powder avalanches have been recorded at the test site, Vallée de la Sionne, Switzerland. The high-spatial-resolution photographs, acquired from two different observation angles, allow us to measure the velocity and height of plume-and-cleft structures on the powder-cloud surface. The photogrammetric measurements are supplemented by airborne laser scans of release, entrainment and deposition zones before and after the artificial avalanche release. Even though the precision of the photogrammetric measurements is limited, they are the best data available to test models of powder snow avalanche dynamics. The laser scan data capture initial and boundary conditions while time series of photogrammetric measurements provide insight into mechanisms driving blow-out formation and inertial propagation of the cloud. In this paper we present the experimental measurements and make direct comparisons with model simulations.

We describe changes in glaciers of the Balkhash-Alakol basin, central Asia, and analyse unified glacier inventories of the Zailiyskiy-Kungei and Jungar glacier systems and the Chinese part of the Ili river basin, as well as mass-balance monitoring data from Tsentralniy Tuyuksu glacier for the period 1957-2014. In spite of significant inter-basin differences, glaciation of the three glacial systems in the Ili river basin within Kazakhstan as well as within Chinese territory is changing simultaneously and similarly. Differences in the rates of glacier degradation are small and are affected primarily by the orientation of the flanks of the mountain ridges. Since the mid-1950s, glaciation of the region has remained degraded and, on average over the period examined, glaciers shrank at a rate of about 0.8% a-1 in area and about 1 % a-1 in ice volume. Glacial systems in large basins such as Balkhash-Alakol change simultaneously, linearly and at similar rates. The average rates of glacier reduction of the Zailiyskiy-Kungei, Jungar and upper Ili glacier systems for the period 1955/56-2008 amounted to 0.76%, 0.75% and 0.73% a-1 respectively.