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Light-absorbing particles in the Himalaya

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.

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 thesis can be downloaded here.


Socio-economic development key driver future South Asian water gap

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.

Spatial precipitation patterns resolved with atmospheric modelling

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.

P.N.J. Bonekamp, E. Collier, W.W. Immerzeel (2018), The Impact of Spatial Resolution, Land Use, and Spinup Time on Resolving Spatial Precipitation Patterns in the Himalayas, Journal of Hydrometeorology, 19, 1565-1581.


Model output compared to the observations for the summer (left panels) and winter period (right panels).


The effect of spatial resolution for the simulated winter and summer period.

PhD degree for Philip Kraaijenbrink

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.

Walter Immerzeel to receive the James B. Macelwane medal

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.

About Immerzeel

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.

Award ceremony

“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.


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