Dr Walter Immerzeel gives a lecture on geographical hydrology, titled: 'Drones on the Roof of the World'.
If I can unravel and model these two diverse climate systems, we can try to scale them up for all of the Himalayas.
Walter Immerzeel
Walter Immerzeel

For a scientist, physical geographer Walter Immerzeel looks remarkably tanned and fit. Not surprisingly – he travels regularly to Nepal. Up on the roof of the world, he studies the impact of climate change on glaciers and associated water resources. More than 25% the world’s population depends on meltwater from the Himalayas, yet we still know very little about the dynamics in high mountain areas. A recently awarded ERC starting grant will enable Immerzeel to take measurements in two contrasting locations: the Karakoram and the Himalayas. Something strange is going on in the Karakoram mountain range. It is virtually the only mountainous area in the world where glaciers are actually growing.
Text: Youetta Visser


Using drones and other instruments, Immerzeel braves freezing-cold temperatures at high altitudes. “It is inhospitable terrain. The surface of the glaciers is strewn with rubble – boulders sometimes five metres high. And the glaciers move! It’s difficult to take measurements on site. We’re the first researchers to use drones. They fly 100 to 200 metres above the glaciers and take overlapping photographs. But at this altitude, they fly faster and are less stable because the air is thinner. Therefore, for each photo, a record is maintained of the angle at which it was taken. We then use special software to map the whole glacier.” In addition to drones, Immerzeel uses a wide range of other instruments including satellite images, Pluvio rain gauges, pressure gauges in the rivers and snow sensors that measure the thickness of the ice using sound waves. “The VENI grant that I was awarded previously afforded little leeway to purchase instruments. Luckily I work closely with a research group from Zurich and with ICIMOD, an international organisation based in Nepal. Together, we’ve been building weather stations in the field since 2009.” These stations sit at an altitude of 5,000 metres; it takes Sherpas days to carry the equipment up the mountain.

The Karakoram

“I’ve already taken measurements in the Langtang region – I even lived there for a while. It has a monsoon climate, where the annual amount of rain falls within just a few months. As the surface of the glacier grows, the ice beneath the glacier melts. The Karakoram range is new for me. It’s slightly higher and has a different climate. The glacier melts steadily for part of the year and then grows again during the other months.” Nobody knows why the glaciers in the Karakoram expand again. “It would be great if we could explain this and solve the Karakoram anomaly. This should be possible now that we are using atmospheric models at an unprecedented level of detail and entering measurements we have gleaned from the area into existing models.”


Immerzeel is also working to improve the existing models. “For example, sublimation – the direct conversion of snow into its gaseous form – has yet to be accounted for in these models. This could explain why the glacier shrinks by as much as 30% during winter. We’re also developing a new algorithm for the dynamics of the glacier, for example the downhill flow and internal deformation of the ice. Cartesius, an NWO supercomputer, is taking care of all the calculations.” The research team also devotes special attention to aligning the measurement results. “In the photos taken by the drones, 1 pixel covers a surface area of 20 by 20 centimetres, while satellite images are 100 times less detailed. Scaling up the measurement results is a research project in itself.”


The ERC study unites three disciplines: hydrology, glaciology and meteorology. “After the IPCC – the UN climate organisation – made a serious error in predicting that all glaciers in the Himalayas would probably have vanished by the year 2035 (which is of course complete nonsense), it became clear that there was a lack of measurement data at high altitudes. Our measurements serve as benchmarks to better model the past. We then superimpose a number of climate scenarios on these models and attempt to predict the impact of climate changes.” Does Immerzeel foresee many natural disasters? "Our water resources are more or less guaranteed until the end of this century. However, the composition of this water – the ratio of rainwater, meltwater and groundwater – will change. And the peaks and troughs in supply will become greater since the glacier’s ability to serve as a buffer will diminish, to mention but one aspect. I do expect more flooding.”

Immerzeel knows exactly what direction his work is taking. “If I can unravel and model these two diverse climate systems, we can try to scale them up for all of the Himalayas. But that’s for a future project.”