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High Mountain Glaciers and Hydrology (HIMAL)

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Glacier shrinkage is one of the most striking signals of climate change and has profound impacts for downstream and coastal communities. High altitude glaciers, difficult to access and little understood to date, play a key role in contributing to streamflow in many of the poorer regions of the world. For these areas, where water is a vital supply for crops and communities, understanding changes in high-altitude cryosphere is crucial to assess vulnerability to future climate change.

We use a synthesis of observational methods to span scales of cryospheric and hydrological change, from local, process-oriented field research to catchment- and regional-scale remote sensing. We use these observations to drive physically-based radiative, glacier and hydrological models for the recent past, present day, and into the future. Our research seeks to understand key processes in distinct study sites, and we leverage novel observations and understanding to produce robust ablation and streamflow projections for the Alps, Andes, and across High Mountain Asia. Understanding debris-covered glaciers and their role in the water cycle has been a key recent focus.

Projects

	RAVEN - Rapid mass loss of debris covered glaciers in High Mountain Asia One of the most important questions of climate change impact research today is how glaciers are responding to global warming. ERC-funded, RAVEN aims to determine the role that debris-covered glaciers play in the water cycle of High Mountain Asia and better incorporate processes unique to debris-covered glaciers into regional assessments of future runoff projections.
	Glaciers, snow and the hydrology of the dry Andes of Chile Together with researchers at University of Chile and Centro de Estudios Avanzados en Zona Arida (CEAZA), we combine field observations and modelling to understand the cryospheric importance and trends of glacier and runoff changes in the dry Andes of Chile. Our current research activities are focused on 1) modelling recent and future changes in glaciers and high-mountain runoff, 2) determining the importance of snow sublimation for the water balance in this arid region, and 3) understanding snow accumulation and seasonal snow in the catchments.
	Mapping global debris cover and changes in debris-covered area over the satellite era Debris-covered glaciers are common in many mountain ranges. Debris considerably alters the response of glaciers to climate, but supraglacial debris distribution is still not documented at the global scale. Debris-covered glaciers are notoriously difficult to delineate due to their fuzzy boundaries and spectral similarities to marginal moraines. Their surface is often characterized by supraglacial ponds and exposed ice cliffs, whitch contribute disproportionately to their melt. Ongoing research has worked to develop robust, automated routines to delineate the debris-covered area and to identify their dynamic surface features from multispectral satellite data and high-resolution digital elevation models.
	Understanding glaciers and hydrological changes in the Tibetan Plateau using high resolution monitoring and modelling This collaboration with the Institute of Tibetan Plateau Research (ITP), Delft University and Northumbria University is supported by a Newton Advanced Fellowship by the Royal Society (UK) and an European Space Agency (ESA) project and aims to advance understanding of the cryosphere and hydrology of high elevation catchments on the Tibetan Plateau. Combining comparative modelling, satellite and field-based methods, the study focuses on several glaciers and catchments across the Tibetan Plateau. The project also makes use of repeat UAV surveys and field methods on Glacier 24K and Parlung Glacier in the upper Yarlung Tsangpo catchment to investigate the effect of debris cover on mass balance rates in the region, to understand differences between debris-covered and debris-free glaciers.
	High-elevation precipitation in High-Mountain Asia High-mountain precipitation is a key variable for simulating glacier runoff in High-Mountain Asia but is poorly known and difficult to measure directly. This project combines in-situ data with glacier mass balance and hydrological models in order to reconstruct high-mountain precipitation in High-Mountain Asia, investigating the quantity, seasonality and variability of precipitation in selected catchments, and determining the mechanisms that cause or modify these characteristics.
	Peru GROWS – Peruvian glacier retreat and its impact on water security Peruvian glaciers are an important water resource for downstream populations and have shrunk significantly in recent decades in response to climatic change. This project investigates the impacts of ongoing and projected climatic change on glacier retreat and water resources in Peru’s most glacierised river catchment, and assesses the potential of various adaptation strategies for enhancing the resilience of local communities and ecosystems.

Research in pictures

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Assembling an Automated Weather Station as part of a study of catchment meteorology in Nepal. Photo: Eduardo Soteras

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Testing meteorological instruments on the rugged debris surface of a Himalayan glacier. Photo: Eduardo Soteras

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Supraglacial ice cliffs act as melt hot spots for debris-covered glaciers, and play a key role in determining glacier mass balance. Photo: Eduardo Soteras

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Ponds on the glacier surface regulate discharge from the glacier, but also rapidly absorb atmospheric energy. Photo: Eduardo Soteras

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A research team navigating the debris surface of Lirung Glacier, Nepal. Photo: Eduardo Soteras

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An avalanche descending from 7000 m in Nepal; such avalanches are a principal supply of ice for many debris-covered glaciers. Photo: Evan Miles

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Further information

Staff

High Mountain Glaciers and Hydrology

Dr. Francesca Pellicciotti	teamleader, senior scientist
Ursin Jacob Eberhard	trainee
Adria Fontrodona Bach	visiting scientist
Stefan Fugger	PhD student
Prof. Regine Hock	fellow
Marin Kneib	PhD student
Dr. Michael James McCarthy	Postdoc
Dr. Evan Stewart Miles	Postdoc

MSc topics

1. Mapping supraglacial ponds using SAR data during the monsoon

Supraglacial ponds have been identified as an important component of the hydrological cycle of Himalayan debris-covered glaciers (Miles et al, 2016, 2017; Benn et al, 2017; Irvine-Fynn et al, 2017) and as key contributors to mass loss in the ablation area of these glaciers (Sakai et al, 2000; Salerno et al, 2017; Miles et al, 2018). However, observation of these features during the ablation season has been precluded by the South Asian Monsoon, which brings consistent cloud cover and heavy rainfall, preventing access to field sites and inhibiting optical satellite observations. Satellite-based Synthetic Aperature Radar observations, now readily available at moderate resolution thanks to the ESA Sentinel program, are insensitive to cloud cover and offer the possibility for routine observation of supraglacial hydrology and novel insights into processes. This project aims to develop and validate a method for identifying supraglacial ponds from publicly-available SAR imagery.

2. Examining the debris cover anomaly at Nyanang Phu Glacier, Tibet

Supraglacial debris has been widely recognized to greatly reduce surface melt by inhibiting the transfer of radiative and atmospheric energy to the ice (e.g. Ostrem, 1959; Nicholson et al, 2006). Yet, paradoxically, glaciers across High Asia appear to be thinning at comparable rates regardless of the presence of debris (e.g. Kaab et al 2012; Gardelle et al 2013). Studies have implicated reduced ice flux, ice cliffs and supraglacial ponds, and glacier elevation differences as contributing factors for this surprising result, but the effects are difficult to disentangle due to differences in setting, size, dynamics, and source areas of glaciers exhibiting thick surface debris or clean ice at the terminus. In this study, we will examine the thinning rates of an unusual glacier in the monsoon-influenced region of Tibet. Nyanang Phu Glacier has two major flow units – one, fed by avalanches, is covered by thick debris, while the other is sourced simply from snowfall and remains clear of debris. The study will determine historic and contemporary thinning rates from satellite stereo imagery, patterns and differences in ice velocity, and specific changes in surface features for this glacier for the last 40 years, then integrate these results to advance our understanding of the effects of surface debris on glacier melt.

3. Ice-cliff detection from high-resolution multispectral satellite imagery

The backwasting of bare-ice cliffs accounts for a disproportionate amount of mass loss for Himalayan debris-covered glaciers (Immerzeel et al, 2014; Thompson et al, 2016; Brun et al, 2018). However, our ability to understand the formation and dynamics has been limited by time-consuming manual delineation over successive images. The manual digitization process is not only time-intensive, but reliant on highly subjective expert knowledge as well as patience. In this project, you will use spectral mixing and object-oriented techniques to develop a probabilistic method to map these features from commercial high-resolution multispectral satellite imagery (i.e. Pleiades or SPOT6/7 data) and moderate resolution public data (e.g. Sentinel-2). The results will be compared to a DEM-based topographic method and used to assess spatial variability of cliffs’ key geometric characteristics (aspect, slope, shape-factor) for multiple sites.

4. Velocity seasonality of high-altitude debris-covered glaciers

Recent advancements have enabled an improved understanding of annual-average glacier velocities in High Mountain Asia (Dehecq et al, 2015) and highlighted the seasonality of glacier velocity for select valley glaciers, even with very low annual rates of motion (e.g. Kraaijenbrink et al, 2016; Benn et al, 2017). Pronounced seasonal variability of surface velocity is a strong indicator for the importance of basal sliding and subglacial hydrology for these glaciers, which is slightly surprising considering their accumulation areas are the highest in the world. However, it remains to be seen how consistent these patterns of glacier motion are, and whether glacier attributed such as size and elevation are major controls. This project will use freely-available high-resolution orthoimagery to determine annual and seasonal surface velocities for a population of glaciers in several zones across High Mountain Asia. The research will then examine the extent and magnitude of seasonal velocity variations to consider the importance of basal motion across the region.

5. Determining the influence of supraglacial debris on the characteristics of runoff from glaciers in Switzerland

The area of supraglacial debris has been observed to increase over glaciers (Bolch et al., 2008; Bhambri et al., 2011; Lambrecht et al., 2011) and this pattern is likely to continue in the future as glaciers slow and thin due to increasingly negative mass balances (Kirkbride and Deline, 2013). Currently it is expected that as climate warms the diurnal amplitude of glacial runoff would increase due to an earlier retreat of the snowline and hence a longer period of ice melt (Escher-Vetter and Reinwarth, 1994). However, there is emerging evidence that glaciers with a significant debris cover have distinct proglacial hydrograph characteristics, specifically a smaller amplitude, longer lag time from peak air temperature to peak runoff and a reduction in the number of peaked diurnal hydrographs compared to clean glaciers (e.g. Li et al., 2016). Therefore, increasing glaciers’ debris-cover may have the opposite effect on hydrographs to what is currently expected, which has implications for water resources and especially run-of-river hydropower schemes. This study will analyse a large dataset of proglacial flow records in Switzerland using a consistent approach, enabling determination of the influence of supraglacial debris on the runoff hydrograph and flow duration curves. More specifically, you will determine the hydrograph characteristics (in terms of shape, timing and amplitude) of runoff from glaciers in Switzerland, then quantify the influence of secondary variables (catchment and glacier size, mean elevation, mean air temperature and mean precipitation rate) on the hydrograph characteristics. You will then statistically determine the influence of supraglacial debris on the proglacial runoff characteristics and quantify the overall difference in the standardised flow duration curve between debris-covered and debris-free glaciers.

6. Deriving debris thickness on Oberaletsch glacier (Swiss Alps)

Numerous models aim to predict glacier evolution in a warming climate by determining the total melt based on energy balance calculations over the glacier surface. Supraglacial rock debris has a major impact on glacier melt by increasing the heterogeneity and process complexity of surface melt. Indeed, a very thin layer of debris will enhance melt by absorbing shortwave radiation that will be directly conducted to the ice, while even a few centimeters of debris are enough to insulate the ice from the incoming radiation and therefore results in reduced melt (Oestrem, 1959; Mattson et al., 1993). Debris thickness is very heterogeneous as debris accumulate by riding the glacier surface from different sources, or being melted out from the ice (McCarthy et al., 2017; Nicholson et al., 2018). Debris thickness therefore difficult to constrain and is one of the major unknowns in glacier melt modeling. This project will progress methods to accurately map debris-thickness using on-site high-resolution UAV thermal imagery, with manually excavated debris pits as a validation. The project comprises a few days of fieldwork on Oberaletsch Glacier (Valais, Switzerland) during which the student will use a FLIR T530 thermal camera to measure debris thickness variations and excavate a number of pits for validation. The data will further be inverted and analyzed to infer debris thickness based on near-surface meteorology, and will later be used to inform models assessing the future thinning of Oberaletsch Glacier.