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Debris cover significantly influences glacier melt rates, but our knowledge of debris physical properties, their variability and their effects on ablation is limited. In-situ measurements on debris-covered glaciers are relatively sparse and therefore literature values are often used in modelling studies. To address this issue, we have compiled DebDab, a database of debris cover properties that includes debris thickness, bulk thermal conductivity, surface roughness, albedo, emissivity, porosity and measured subseasonal melt rates from published literature and datasets. The first version contains debris thickness measurements for 73 glaciers, over 7000 individual debris thickness measurements and more than 1700 melt rate measurements. The other properties have more than 400 entries of which only 45% are actual measurements.DebDab is openly available as a community resource and will continue to develop in the coming years, and we welcome community contributions of their measurements of debris thickness and properties. We hope that it will be useful for physical parameter probability distributions, model uncertainty assessments, and as validation data for debris thickness estimation and melt modelling. To demonstrate its utility, we used DebDab to explore the sensitivity of point scale melt simulations to debris properties variability, and in particular to investigate (1) the effect of changing debris thickness on each debris property; (2) the relationship between debris properties; and (3) whether these relationships are the same for different climatic regions worldwide., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Glaciers in the European Alps recorded exceptional melt volumes in the summer of 2022. Impressions from High Mountain Asia also suggested higher-than-usual mass loss. Our observations at seven hotspots in the Pamir mountains highlighted glaciers suffering from small accumulation areas at the end of the balance year, due to reduced winter snowfall and increased summer melt. The glacier mass budget of this mountain range has been regarded as part of the Pamir-Karakoram Anomaly, but the most recent satellite observations suggest that the Karakoram Anomaly is coming to an end. Here, we draw together field and remote sensing observations to assess the severity of Pamir mass loss in recent years, and in the extreme 2022 summer in particular, as compared to the historical baseline. We examine climatic records and reanalyses to establish the degree to which recent years fit within the observed historic seasonal and annual ranges. We compare the recent to historic mass balance measurements at Abramov Glacier, the single long-term monitoring reference glacier for the region. We combine geodetic glacier mass balances surveyed from a variety of sources to consider how well observations agree with one another. We then consider changes to observed glacier surface albedo and surface temperature over the past 20 years based on satellite record. Finally, we examine interannual and decadal changes to on-glacier and catchment snowlines. Taken together, these data sources enable us to link direct meteorological and glaciological conditions to broad spatial and temporal patterns of change across the Pamir mountains., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

High Mountain Asia (HMA) hosts the largest mass of ice outside the Polar Regions and provides water to large downstream communities. Glacier change has been highly diverse across the region over the last decades, with glaciers in the Pamirs experiencing near-neutral mass balance while fast rates of mass loss are observed in the Southeastern Tibetan Plateau (STP). In a previous modelling study in the STP, we found that precipitation phase changes associated with climate warming were a major accelerator of glacier losses, but this mechanism of mass loss acceleration has yet to be explored across the rest of HMA. High-elevation measurements of precipitation phase are rare, especially along glacierized elevations, which lie at the solid-mixed-liquid boundary during summer months. Therefore, accurate representation of precipitation phase in models is essential for quantifying glacier accumulation rates and projecting change.Here we use downscaled and bias-corrected ERA5-Land reanalysis to show the high sensitivity of the solid precipitation ratio to the choice of parameterisation and its impacts on the seasonality of simulated snowfall accumulation at three glacierized catchments covering distinctive climates in HMA (Kyzylsu in the Northern Pamirs, Trakarding-Trambau in the Nepalese Himalayas and Parlung No.4 in the STP). We then apply a land-surface model at high spatio-temporal resolution (100m, hourly) to show the effect of the precipitation phase parametrization on the simulated glacier-mass balance, snowpack dynamics and catchment hydrology. Our results highlight the need to better constrain precipitation phase in glaciological studies and to consider the uncertainty associated with the choice of parameterisation., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Since 2010, central Chile has experienced one of the driest decadal-scale droughts of the past thousand years, with annual precipitation deficits of 20-40%. In the Andes, this ‘megadrought’ has manifested in acute reductions in snowpack; streamflow; lake, reservoir and glacier volume; and soil moisture, with knock-on effects especially for agriculture and vegetation productivity. While many studies have characterised such impacts via remote sensing, in-situ measurements and conceptual hydrological modelling, fewer have taken a mechanistic approach, leaving room to improve process understanding and disentangle the complex response of the mountain water cycle. Here we present preliminary results from a modelling study of the propagation of the megadrought in the Cajon del Maipo, to the east of Santiago. We simulate water, energy and carbon fluxes both before and during the drought, using the land-surface model Tethys-Chloris, at 250 m spatial and hourly temporal resolution. We force the model with a new meteorological dataset, CHELSA high-res, and evaluate its performance using in-situ streamflow and glacier mass balance data, as well as snow cover and leaf-area index data from satellite images. We explore in particular how reduced snow cover has affected vegetation dynamics and downstream hydrology to gain insights relevant for a snow-scarce future., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Data to support the article Supraglacial debris thickness and supply rate in High Mountain Asia in Communications Earth & Environment by McCarthy and others

The Indian and East Asian Summer Monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature ranges, high atmospheric water content and high precipitation rates. Glacier energy and mass balance modelling using in-situ measurements offer insights into the ways in which surface processes are shaped by climatic regimes. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Central and Eastern Himalaya to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget primarily controls the melt of clean ice glaciers, but turbulent fluxes play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux decreases during core monsoon, but the latent heat flux cools the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes causes debris-covered glacier melt rates to stay almost constant through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface and the turbulent fluxes, which intensify melt during monsoon through surface heating and condensation. Pre monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover lowers the melt rates at high elevation. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget, while informing and motivating further glacier- and catchment-scale research using process-based models.

Melt from supraglacial ice cliffs is an important contributor to the mass loss of debris-covered glaciers. However, ice cliff contribution is difficult to quantify as they are highly dynamic features, and the paucity of observations of melt rates and their variability leads to large modelling uncertainties. We quantify monsoon season melt and 3D evolution of four ice cliffs over two debris-covered glaciers in High Mountain Asia (Langtang Glacier, Nepal, and 24K Glacier, China) at very high resolution using terrestrial photogrammetry applied to imagery captured from time-lapse cameras installed on lateral moraines. We derive weekly flow-corrected digital elevation models (DEMs) of the glacier surface with a maximum vertical bias of ±0.2 m for Langtang Glacier and ±0.05 m for 24K Glacier and use change detection to determine distributed melt rates at the surfaces of the ice cliffs throughout the study period. We compare the measured melt patterns with those derived from a 3D energy balance model to derive the contribution of the main energy fluxes. We find that ice cliff melt varies considerably throughout the melt season, with maximum melt rates of 5 to 8 cm d−1, and their average melt rates are 11–14 (Langtang) and 4.5 (24K) times higher than the surrounding debris-covered ice. Our results highlight the influence of redistributed supraglacial debris on cliff melt. At both sites, ice cliff albedo is influenced by the presence of thin debris at the ice cliff surface, which is largely controlled on 24K Glacier by liquid precipitation events that wash away this debris. Slightly thicker or patchy debris reduces melt by 1–3 cm d−1 at all sites. Ultimately, our observations show a strong spatio-temporal variability in cliff area at each site, which is controlled by supraglacial streams and ponds and englacial cavities that promote debris slope destabilisation and the lateral expansion of the cliffs. These findings highlight the need to better represent processes of debris redistribution in ice cliff models, to in turn improve estimates of ice cliff contribution to glacier melt and the long-term geomorphological evolution of debris-covered glacier surfaces., The Cryosphere, 16 (11), ISSN:1994-0416, ISSN:1994-0424