Our last fieldwork in 2021 involved collecting field data and conducting maintenance work on Trambau and Trakarding glaciers in Rolwaling, Dolakha, Nepal, from 10 November to 2 December. We carried out the fieldwork on behalf of Nagoya University in Japan to ensure the continuity of the long-term data series as the university has been conducting regular bi-annual glaciological and hydro-meteorological measurements on these glaciers since 2016. The team from Nagoya University have not been able to visit the field since autumn 2019 because of the COVID-19 pandemic.

What does it take to keep the data series intact?

Continuity is essential for a glacier mass balance series. If we miss a field visit, then stakes can melt out or be buried by high snowfall. Some meteorological and hydrological stations have data storage that is limited to about a year or so of data. If the data are not downloaded, this can lead to a large gap in observations.

During the fieldwork in November−December 2021, we conducted glacier mass balance observations on Trakarding and Trambau glaciers. We measured or re-installed 13 mass balance stakes at elevations between 5,330 masl and 5,900 masl on debris-free Trambau Glacier, which extends just over 23 km², thus helping to continue the record of glacier mass balance change. Similarly, we measured or re-installed eight mass balance stakes on debris-covered Trakarding Glacier, which is detached from Trambau Glacier and feeds the largest proglacial lake in Nepal: Tsho Rolpa Glacial Lake.

Replace, maintain, record

Understanding how temperature varies with elevation is an essential part of this work. Temperature loggers have been installed at different elevations along Rolwaling Valley, and we located and replaced nine such loggers in Rolwaling Valley. Similarly, several tipping bucket loggers are placed to collect rain data to understand the precipitation regime in the valley. We located and replaced the dataloggers of all seven tipping buckets.

There are two automatic weather stations on the side moraines of the Trambau and Trakarding glaciers, and we downloaded data and carried out routine maintenance work, such as making sure the sensors are working and clearing out debris. Such stations are installed on high mountains to understand the overall climate of the local area and then used in combination with other available meteorological data to analyse the effect of climate change on glaciers.

Time-lapse cameras are installed at various glacier sites to record the visual changes of landscape, glacier terminus, and snow cover. We recovered data from three such cameras on Trakarding Glacier during this fieldwork, and these images tell a story of the constant changes from day to day and season to season. We also recovered two Differential Global Positioning Systems (DGPS) ​from Trakarding Glacier. DGPS are installed to give a continuous record of changes in glacier movement.

Trakarding is not unusual in having debris cover; this is a feature of many glaciers in the HKH region. Debris-covered glaciers respond to different factors differently to climate forcers than do clean glaciers, and a sensor was previously installed to record the changes in temperature/humidity inside the debris-covered part of glacier. We also recovered this sensor.

All these measurements and instruments are essential features of monitoring glacier change. The data collected are then combined to get a comprehensive picture of glacier change and to make projections on changes we may expect in the future.