A number of studies in our group have looked at debris-covered glaciers in recent years. What we have not really done yet is ask where the debris covering all that ice is actually coming from. In a new study, published recently in the Journal of Earth Surface Dynamics we are examining the contribution of sediment from the lateral moraines to the glacier surface.
Using repeat DEMs from multiple UAV flights between 2013 and 2018, we show that debris from the moraines can only reach the margins of the glacier surface but locally contributes to a considerable thickening of the cover.
The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of +0.31m/year during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (+0.39 m/year) than in the dry season (+0.23 m/year).
The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, due to both the melt of ice below and mass wasting processes at the surface. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m/year along a narrow margin of the glacier surface. Here the observed debris thickness is approximately 1 m, reducing melt rates of underlying glacier ice.
We recently published a new paper, led by Maxime Litt, providing guidelines for glacier-ablation modelling in HMA environments.
The conventional Temperature index (TI) models for modelling glacier ablation require few input variables and rely on simple empirical relations. The approach is assumed to be reliable at lower elevations (below 3500 m above sea level, a.s.l) where air temperature relates well to the energy inputs driving melt. Using field meteorological observation in Langtang and Khumbu, we show that temperature relates poorly to a number of important mass-loss drivers in high-altitude, so that temperature indexes have to be handled with care.
At the high elevation glaciers in Mountain Asia (HMA), we observed that incoming shortwave radiation is the dominant energy input and the full surface energy balance model relates only partly to daily mean air temperature. During monsoon surface melt dominates ablation processes at lower elevations (between 4950 and 5380 m a.s.l.). As net shortwave radiation is the main energy input at the glacier surface, albedo and cloudiness play key roles while being highly variable in space and time. For these cases only, ablation can be calculated with a TI model. Sublimation and other wind-driven ablation processes are important for mass loss, and remain unresolved with such simple methods. Ablation modeled with a SEB can diverge from the observations, but a suitable value for surface roughness can solve the issue.
Cumulated ablation calculated with the surface lowering measurements (thick blue line), with the surface energy balance for changing z0 values (orange dashed and continuous lines), with the TI (red line) and ETI (clear blue line) with one fixed set of factors. The hourly wind speed is shown upside down (green curve). Periods of surface melt (Ts = 0) are highlighted in orange. Results from Mera Glacier, 5380 m a.s.l in 2014 and 2017 (a) from Yala Glacier, 5350 m a.s.l., in 2014, 2016 (b) and Mera Glacier, 6352 m a.s.l, in 2015 and 2016 (c).
For her master thesis research Kari-Anne studied the sources of light-absorbing particles in the Langtang Valley in Nepal in the Himalaya. The study showed that most light-absorbing particles consisted of local material.
When light-absorbing particles (LAPs) deposit on a glacier surface, they decrease the albedo of ice and snow, resulting in increased melt. Glaciers in high mountain areas in the Himalya are influenced by this effect. Many studies assume that the main source of the LAPs is pollution, like black carbon (BC), from the Indo-Gangetic plain. However, this is uncertain. During this study, field work, microscopic analysis and (large-scale) remote sensing images were used to determine the main source of LAPs in the study area.
Light-absorbing particles in the Himalayas - YouTube
The results of the field work and the microscopic analysis showed that most LAPs consisted of natural sources like silicates and aluminosilicates. Only a few black carbon particles were present in the samples. The remote sensing images showed high concentrations of BC at the Indo-Gangetic plain but the concentrations for BC in the field work area were very low. These results make it very unlikely that high concentrations of LAPs at the Indo-Gangetic plain reached the study area during the field work period. Further research is needed to determine if LAP concentrations during other seasons are also dominated by local material.
The recent United Nations Climate Change Conference COP24 held in Katowice, Poland once more demonstrated the world’s climate change concerns. In the Indus, Ganges, and Brahmaputra river basins, a global climate change hotspot and home for about 900 million people, these concerns are pressing, since the river systems provide water resources for the important agricultural, domestic, and industrial sectors that serve these people. Melt water from glaciers and snow feed the headwaters of these rivers and are strongly influenced by rising temperatures. In addition, the monsoon and its dynamics, which determine the regional hydrology, are expected to change. Moreover, strong socio-economic developments and a rapid and continuous population growth will result in tremendous increases in water demand and cause pressure on water resources. It is therefore very likely that a water gap will develop in the future.
A new study published (open access) in Hydrology and Earth System Sciences led by René assesses the combined impacts of climate change and socio-economic developments on the future “blue” water gap in the Indus, Ganges, and Brahmaputra river basins until the end of the 21st century. In this joint effort by FutureWater, Utrecht University, Wageningen Environmental Research and ICIMOD a hydrological model that simulates future changes in the upstream water reserves (SPHY) is coupled with a hydrology and crop production model that simulates future changes in the downstream water balance (LPJmL). The models were forced with the latest climate change projections and socio-economic scenarios.
The findings of this study indicate that the surface water availability will increase, which can mainly be attributed to increases in monsoon precipitation. Besides the increases in surface water availability, water consumption by irrigation will most likely decline due to shorter growing seasons that emerge from temperature increases, and a shift from blue water irrigation to green water/rainfed irrigation due to increases in precipitation. However, this increase in water availability cannot outweigh the strong increases in water demand that are associated with the strong socio-economic development, and will thus likely lead to a substantial increase in the water gap with 7% and 14% in the Indus and Ganges river basins, respectively, during the 21st century. This implies the importance of robust adaptation strategies to cope with future water shortages in the region.
Maps showing the annual groundwater depletion for the reference period (a) and the projected changes in groundwater depletion for RCP4.5 (b), RCP8.5 (c), RCP4.5 – SSP1 (d), and RCP8.5 – SSP3 (e). The projected changes are given for the end of the 21st century. Green indicates less depletion and red indicate more depletion.
Our new open access study, led by Pleun, shows the importance of subkilometer atmospheric modelling and correct surface boundary conditions in areas with complex topography to accurately estimate catchment-scale meteorological variability.
Frequently used gridded meteorological datasets poorly represent precipitation in the Himalayas because of their relatively low spatial resolution and the associated representation of the complex topography. Dynamical downscaling using high-resolution atmospheric models may improve the accuracy and quality of the precipitation fields. Therefore, we have used the Weather Research and Forecasting (WRF) Model to determine the resolution that is required to most accurately simulate monsoon and winter precipitation, 2-m temperature, and wind fields in the Nepalese Himalayas.
Results show that a high resolution of 500 m is computationally still feasible and provides the best match with the observations, gives the most plausible spatial distribution of precipitation, and improves the quality of the wind and temperature fields. Our findings suggest that, in combination with future improvements to atmospheric models for applications in complex terrain, subkilometer grid spacing may resolve catchment-scale meteorological variability more accurately. This will improve our capabilities to study glacio-hydrological changes at catchment and larger scale. Future modeling studies of High Mountain Asia should consider subkilometer grids to accurately estimate local meteorological variability.
Wednesday September 19th Philip successfully defended his PhD during the formal Utrecht University defense ceremony and he may now call himself Dr. Kraaijenbrink.
Philip has received his PhD with distinction for his thesis titled High-resolution insights into the dynamics of Himalayan debris-covered glaciers in which he improved our understanding of debris-covered glaciers by studying them in detail with unmanned aerial vehicles and modelling. The thesis is available for open access download via the Utrecht University library.
Philip was supervised by Prof. Steven de Jong, Dr. Walter Immerzeel and Dr. Joseph Shea. The external defense committee was formed by Prof. Andreas Kääb, Prof. Etienne Berthier, Prof. Koji Fujita, Prof. Michiel van den Broeke and Dr. Francesca Pellicciotti.
Prof. dr. Steven de Jong provides Philip with his degree in the formal Utrecht University tradition.
The American Geophysical Union (AGU) has awarded Dr Walter Immerzeel the James B. Macelwane medal for his outstanding research into the water balance of the Himalaya mountain range. He is also being given the singular honour of being made an AGU fellow. The AGU bestows the award annually on a maximum of five outstanding early career scientists for their major contributions to the geophysical sciences.
What is the connection between climate change, water, glaciers, snow and the atmosphere? To find an answer to this question, 43-year-old Walter Immerzeel carries out research in the Himalayas, which are dubbed the water tower of Asia. Over a quarter of the world’s population is dependent on the water of this enormous mountain range and this makes it immensely important to understand how the processes involved impact each other.
Charting the water tower
Immerzeel is, for example, using drones to chart the mountain range’s giant glaciers. He employs other instruments to measure things such as the thickness of the ice, the amount of rain and snow, and the temperature and amount of water in the rivers. He uses all this data to improve existing hydrological models, so that better forecasts can be made of how the provision of water will change in the future.
Immerzeel obtained his doctorate in physical geography in 2008 from Utrecht University. As a post-doctoral researcher, he received an NWO Veni grant and worked for many years for organisations including the International Centre for Integrated Mountain Development which advances research on the Himalayas. He went on to work for three years at ETH Zurich, returning to Utrecht University in 2014. At Utrecht, Immerzeel was awarded grants including an ERC Starting Grant in 2015 and an NWO Vidi grant in 2016.
“The medal is seen as one of the most important awards for young geoscientists,” Immerzeel explains. “Part of the prize is that I get the honour of giving a Union Lecture during the AGU Fall Meeting in December this year. It will be a lecture on my research and will be open to all 25,000 colleagues attending the congress.” It is during the congress that Immerzeel will be actually awarded the medal.
The James B. Macelwane medal
The James B. Macelwane medal has been awarded by the AGU since 1961 and is named in honour of the US seismologist, James B. Macelwane (1883 – 1956). Macelwane was president of the AGU from 1953 until his death in 1956.
The eddy covariance tower on Yala Glacier after installation in October 2016 (Photo: Walter Immerzeel).
Our new study, which was led by Emmy and published in Frontiers in Earth Science, shows that snow sublimation should no longer be ignored in future hydrological and mass balance studies in the Himalaya. We assessed the importance of snow sublimation to the water and mass budget of Yala Glacier in the Langtang Valley, Nepalese Himalaya.
From a hydrological and glaciological perspective, snow sublimation is a loss of water from the snowpack to the atmosphere. So far, snow sublimation has remained unquantified in the Himalaya, prohibiting a full understanding of the water balance and glacier mass balance. Hence, we measured surface latent heat fluxes with an eddy covariance system on Yala Glacier (5350 m a.s.l) to quantify the role snow sublimation plays in the water and glacier mass budget.
The observed sublimation is 32 mm for a 32-day period from October to November 2016, which is high compared to observations in other regions in the world. The bulk-aerodynamic method was used to estimate cumulative sublimation and evaporation at the location of the eddy covariance system for the 2016–2017 winter season, which is 125 and 9 mm respectively. This is equivalent to 21% of the annual snowfall.
A combination of meteorological observations and WRF simulations were used to estimate the spatial variability in sublimation. These simulations reveal that sublimation is primarily controlled by wind speed. The daily cumulative sublimation is a factor 1.7 higher at the ridge of Yala Glacier, which is wind-exposed, compared the location of the eddy covariance system. This is a considerable loss of water and illustrates the importance and need to account for sublimation in future studies in the Himalaya.
This work quantifies surface sublimation only. However, sublimation may be enhanced under conditions with wind-induced snow transport. Therefore, future research will focus on including this component to fully assess the importance of snow sublimation in the high-altitude water cycle.
Scatter plots of meteorological variables against sublimation rate, observed at AWS Yala Glacier. The color of the data points refers to the observed wind speed. Results show that vapor pressure deficit and wind speed are the best sublimation predictors.
A new study led by Philip presents a method to map surface temperatures of a debris-covered glacier with an unmanned aerial vehicle (UAV), which has potential to study melt processes of such glaciers. It was published open access today in Frontiers of Earth Sciences.
In the paper we map surface temperatures of Lirung Glacier in three flights on a morning in May 2016. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous ground-based temperature measurements and with Landsat 8 thermal satellite imagery.
Surface temperatures vary greatly both spatially and temporally and have a large range of 50 °C over course of the morning. Statistical analysis shows that the variability is largely independent of incoming radiation and topography, and that much of the signal in surface temperature originates from variation in properties of the debris. Future research of surface melt processes can utilize this data to further unravel heterogeneous melt patterns on debris-covered glaciers.
Surface temperature orthomosaics of the three UAV flights on 1 May 2016 (A–C; 06:45, 09:20, and 10:35) and the brightness temperature of the Landsat 8 band 10 on 2 May 2016 at 10:32.
Comparison of the average warming rate (f) over the surveyed glacier surface area with five different DEM derivatives: aspect (a,g), slope (b,h), upstream area (c,i), relative local elevation (d,j), and mean incoming shortwave radiation (e,k). The relative importance of each variable as a predictor in a random forest regression is shown in (l)
Animation of ground-based thermal imaging of an ice cliff and its surroundings, performed synchonous to the UAV flights.
Recent observations show that the surging tongue of Khurdopin glacier in Shimshal catchment in Northern Pakistan has caused a lake to form in 2017 (Steiner et al. 2018), which might return annually in subsequent years following the melt season. Ongoing monitoring has shown that the lake expanded since November 2017 reaching a constant area of ca 350 000 m2 in March of 2018 and it has remained stable since. As the ice masses from the surge will take many more months to melt the lake is likely to remain or reappear even after drainage events. As the melt season starts the lake may drain and this may cause flooding downstream, in particular close to the village of Shimshal, the adjacent agricultural areas and lake Attabad located further downstream.
To assess potential damage from a lake burst an initial BASEMENT hydrodynamic model was constructed for the area using available elevation models , estimated lake water volumes and dam breach scenarios from literature and an initial model simulation assuming a lake volume of 7 million m3 and a short breach period was conducted. The movie below shows the maximum inundation depth as the wave travels through the valley.
SuddenBreach 3500 - YouTube
Subsequent work will focus on the following:
Improve the cross profiles using field data or high resolution DEMs (e.g. ALOS-PRISM)
Extend the model run until Attabad lake and assess the potential flood wave there.
Include multiple volume and lake growth scenarios
Include multiple breach scenarios ranging from a catastrophic, near instantaneous breach to a more gradual scenario
Include more detailed exposure data such as infrastructure, houses, agricultural areas