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After the polar ice caps, the Himalayas (‘abode of snow’ in Sanskrit) have the largest number of glaciers.
More than 30,000 square kilometers of mountain range is covered by glacial ice.
These glaciers are a focus of public and scientific debate related to the effects of climate change. Prevailing uncertainties are of major concern because some projections of their future have serious implications for water resources.
This fascinating research project uses the Kipp & Zonen CHR4 radiometer.
One of the most closely studied areas is the Langtang Valley, a catchment of nearly 600 km on the border with China and a quarter of which is covered by glaciers. The highest point is the Langtang Lirung, at 7,234 meters a peak, feared and revered by mountaineers because of the difficulty in reaching the summit.
Most of the rain falls in summer when the monsoon hits the Indian subcontinent and the Langtang region is on its northern frontier, before the Tibetan Plateau. During winter, in the areas above 4,000 meters, many meters of snow accumulate each year and most of it is melting at very fast rates.
Studies of precipitation and melt in the valleys of the Nepalese Himalaya are a collaboration of the International Centre for Integrated Mountain Development (ICIMOD), the Nepalese Department of Hydrology and Meteorology, Kathmandu University, and Utrecht University in the Netherlands.
This work has been continued for many years, currently funded by the Norwegian Government, European Research Commission and the Netherlands Organization for Scientific Research. The team is international, comprising of Nepali, Dutch, Belgian, Finnish, Norwegian, German and Austrian co-workers studying the local climate, glaciers, snow cover and how it all relates to water resources.
The project team maintains a number of automatic weather stations (AWS) in the Langtang River catchment on the border with China that help us to judge the quality of larger data sets derived from satellites. The site is visited twice every year to maintain the stations and conduct field experiments. Data is used to make very detailed studies of melt and precipitation in the valley.
The highest automatic weather station is located at 5,200 meters above sea level on the Yala Glacier. Bi-annual glacier mass balance measurements there are among the most detailed in the Himalaya, making it one of the most important sites to help understand the future of glaciers in the region based on field measurements.
The automatic weather station measures air temperature, relative humidity, wind speed and direction, snow depth, as well as all four radiation components with a Kipp & Zonen CNR4 net radiometer.
This data helps in the understanding of the local meteorological drivers of glacier mass change. Yala Glacier overall is losing mass. This is due to intense solar radiation and dry and windy conditions that facilitate snow and ice melting and sublimation (the phase change from solid to gas without going through the liquid state).
Maintenance of the AWS at this high elevation can be tricky; temperatures in winter fall below -20°C and wind speeds can be very high. Our team visits the station twice a year, before and after the monsoon, to read out data and check equipment functionality.
On clear days, solar radiation at this altitude is fierce. The reflection from the white snow feels like a grill, even when air temperatures are just above the freezing point. When ablation of snow and ice is very strong in the summer, the metal poles of the weather station often need to be re-drilled into the ice by three to four meters. This is to prevent it from melting out and falling over, and potentially damaging sensors like the CNR4 in the process.
Getting data from these stations is not technically difficult, but the local conditions are a challenge. Oxygen levels are 50% lower than in the Netherlands, and that has an effect on one’s concentration. Combine this with freezing temperatures in the morning and the beating sun in the afternoon and you have quite difficult operating conditions.
The CNR4 is an essential centerpiece of the measurements, and it is running on three of the weather stations. It allows the measurement of incoming short-wave radiation - the major driver for ice and snow melt. At the same time it also records the out-going shortwave radiation, from which we deduce the albedo of the ice or snow cover, a variable that is essential to understand melt events.
While short-wave radiation is measured on many stations and can also be relatively easily modelled, the CNR4 provides insights into a much more challenging variable - long-wave thermal radiation, coming from the atmosphere, clouds and the surrounding terrain. The data analysis is ongoing and in the future will hopefully help give a better understanding of the processes leading to runoff in a changing climate.
After installing new sensors for so many field seasons, the main focus now lies on maintaining these setups and analyzing the data. Future endeavours will hopefully lead to other areas to see whether insights gained here over the years are applicable elsewhere.
Collaborations with local and international partners are key to that, an effort that takes much time in meetings but makes work on these stations even more exciting.
Written by By Jakob F. Steiner, PhD candidate, Faculty of Geosciences , Utrecht University
Find out more about ICIMOD at www.icimod.org and the Utrecht University mountain hydrology projects at www.mountainhydrology.org
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