After the polar ice caps, the Himalayas (which means ‘abode of snow’ in Sanskrit) are known to have the largest number of glaciers right covering over 30,000 square kilometers of the mountain range. These glaciers are a focus of public and scientific debate associated with the effects of climate change
Common uncertainties are of major concern since some predictions of their future have serious implications for water resources. The Langtang valley, a catchment of almost 600 km2 on the border with China and a quarter of which is covered by glaciers, is one of the most closely studied regions. Langtang Lirung is the highest point; standing at 7,234 meters it is a peak revered and feared by mountaineers due to the difficulty in reaching the top.
Langtang Valley in the Himalayas
Rain falls mostly in summer when the monsoon hits the Indian subcontinent and the Langtang region lies on its northern frontier, before the Tibetan Plateau. During winter, several meters of snow build up every year in the areas above 4,000 meters, and a majority of it is melting at very rapid rates.
Weather stations across the Nepalese Himalayas
Researches on precipitation and melt in the valleys of the Nepalese Himalayas are a collaboration of the Nepalese Department of Hydrology and Meteorology, the International Centre for Integrated Mountain Development (ICIMOD), Utrecht University in the Netherlands, and Kathmandu University in Nepal.
The work, currently funded by European Research Commission, the Norwegian Government, and the Netherlands Organization for Scientific Research, has been going on for several years. The work is led by an international team that includes Nepali, Belgian, Dutch, Norwegian, Finnish, Austrian, and German co-workers exploring the local climate, snow cover, glaciers, and how it is all related to water resources.
The project team maintains several automatic weather stations in the Langtang River catchment on the border with China that help to judge the quality of larger datasets obtained from satellites. The team visits the region twice every year to maintain the stations and carry out field experiments and they use the data to make an in-depth analysis of precipitation and melt in the valley.
The highest automatic weather station is situated at 5,200 meters above sea level on the Yala Glacier, where bi-annual glacier mass balance measurements are among the most detailed in the Himalayas. This makes it one of the most significant sites to help understand the future of glaciers in the area based on field measurements. The AWS measures relative humidity, air temperature, snow depth, wind speed and direction, as well as all four radiation components using a Kipp & Zonen CNR4 net radiometer.
This data assists in understanding the local meteorological drivers of glacier mass change. On the whole, Yala Glacier is losing mass because of intense solar radiation and dry and windy conditions that facilitate ice and snow melting and sublimation (the phase change from solid to gas without going through the liquid state).
Kipp & Zonen CNR4 net radiometer
Maintenance on Site, Twice a Year
It can be difficult to maintain the automatic weather station at this high altitude; wind speeds can be extremely high and temperatures can fall below -20 °C during winter. The team visits the station twice a year, before and after the monsoon, in order to read out the data and check equipment functionality.
On clear days, solar radiation at this altitude is severe and the reflection from the white snow feels like a grill even when air temperatures are only above the freezing point. When there is intense ablation of ice and snow during summer, the metal poles of the weather station often have to be re-drilled into the ice by three to four meters so that it doesn’t melt out and fall over, and potentially damage sensors like the CNR4 in the process.
While it is not technically difficult to obtain data from these stations, the local conditions present a problem. Oxygen levels are 50% less than that of the office in the Netherlands, and that have an impact on one’s concentration. In addition to this, freezing temperatures in the morning and the beating sun in the afternoon make operating conditions rather difficult.
CNR4 irradiance measurements over snow and ice during the monsoon season
How the CNR4 Comes into Play
The CNR4 net radiometer is an indispensable center-piece of measurements, and the team has it running on three of the weather stations. It enables them to measure incoming short-wave radiation which is the key driver for snow and ice melt. Simultaneously, it also records the out-going shortwave radiation, from which the team infers the albedo of the ice or snow cover, a variable that is necessary to understand melt events.
Although short-wave radiation is measured on many stations and can also be quite easily modeled, the CNR4 offers a better understanding of a much more challenging variable - long-wave thermal radiation, coming from clouds, the surrounding terrain, and the atmosphere. The data analysis is ongoing and in future will hopefully help the team to better understand the processes resulting in runoff in a varying climate.
Following the installation of new sensors for numerous field seasons, the team is now mainly focusing on maintaining these setups and analyzing the data. Furthermore, future endeavors will hopefully lead the team into other areas to see if insights gained here over the years are relevant elsewhere. The key to that are collaborations with local and international partners. Although this effort takes much time in meetings, it makes work on these stations even more exciting.
This information has been sourced, reviewed and adapted from materials provided by Kipp & Zonen.
For more information on this source, please visit Kipp & Zonen.