Dr. Rijan Bhakta Kayastha
Himalayan Cryosphere, Climate and Disaster Research Center (HiCCDRC)
Department of Environmental Science and Engineering, School of Science, Kathmandu University, Dhulikhel, Kavre, Bagmati Province, NEPAL
Nepal is rich in water resources because of its monsoon, snow-covered area, and a number of glaciers in the Himalayas. However, the hydrological responses of the snow-covered and glaciated zones are distinct from the other zones of Nepal. The water resource of Nepal is heavily dependent on monsoon dynamics and the state of the snow and glacier ice in the Himalayas. Climate change affects both monsoon dynamics and snow and glacier ice in the Himalayas. In addition to this, climate change is also responsible for the increasing number of glacial hazards recently in Nepal.
Glacier is a moving body of snow and ice that has been formed as a recrystallization of snow and a glacial lake is a lake that is formed by glacial activity. Glacial hazard includes any hazard in a glaciated region such as snow and ice avalanche, flash flood due to supraglacial lake draining, and rapid melting of snow and ice of a glacier, Glacial Lake Outburst flood (GLOF), ground subsidence due to rapid thawing of permafrost and heavy snowfall in a glaciated region, etc.
Many studies have shown retreat of glaciers, expanding existing glacial lakes and forming new lakes and altitude of a lower limit of permafrost are shifting upward in the Nepal Himalayas. There are 19 glacierized sub-river basins from east to west in which there are 3,808 glaciers and 2,070 glacial lakes in Nepal (Bajracharya et al., 2020). Total 47 glacial lakes in Nepal, Tibet, China, and India are classified as Potentially Dangerous Glacial Lakes to Nepal because if these glacial lakes are drained, the flood water will enter into Nepal and damage considerably. Out of 47 potentially dangerous glacial lakes in the Himalayas, 25 are in Tibet, China, 21 in Nepal, and 1 in India. This renders much of the infrastructure along the rivers originating from these lakes at immediate risk.
A 2011 study by ICIMOD reported 24 GLOF events in the past, 14 of which had occurred in Nepal, while 10 were caused by overspills due to flood surges across China (TAR)‒Nepal border (ICIMOD, 2011). On 4 August 1985, a Dig Tsho GLOF event swept away three persons, one hydropower plant, 14 bridges, and 35 houses along the Dudh Koshi River. Table 1 shows major GLOF events since the 1980s that have caused damages in Nepal. Since GLOF events are increasing recently, in order to reduce the risk from such events again the Department of Hydrology and Meteorology, Government of Nepal has reduced the water level of Tsho Rolpa Glacial Lake in Dolakha district by 3 m in 2000 and that of Imja Glacial Lake in Solukhumbu district in 2016 by 3.4 m successfully.
Table 1. GLOF events since the 1980s that have caused damages in Nepal.
|S. No.||Date||River basin||Location|
|1||23 June 1980||Tamor||Nagma Pokhari|
|2||11 July 1981||Bhote Koshi||Cirenmacho Lake, Zhangzangbo Valley|
|3||4 August 1985||Dudh Koshi||Dig Tsho|
|4||12 July 1991||Tama Koshi||Chubung|
|5||3 September 1998||Dudh Koshi||Sabai Tsho (Tam Pokhari)|
|6||5 July 2016||Bhote Koshi||TAR, China|
|7||20 April 2017||Barun Valley||Near Lower Barun|
In the recent past, also a few flash flood events in the glacierized river basins of Nepal are occurring mainly due to irregular monsoon activity and sudden warming epochs in some regions. Seti flash flood on 5 May 2012 due to snow, ice, and rock avalanche, a Glacial Lake Outburst Flood (GLOF) on 5 July 2016 in Bhotekoshi River in Tibet, China, and a flash flood on 20 April 2017 in Barun River are a few examples. Such events have increased the risk of glacial hazards, especially in the high mountain areas. Therefore, it is high time to monitor weather, snow, glaciers, glacial lakes of the high Himalayas by establishing suitable stations and need to install early warning systems in downstream of such glacierized river basins in Nepal.
Snow and weather monitoring stations at high altitudes will be also useful to analyze possible snow hazards and then flash floods in the downstream as such occurred in Seti River in Nepal on 5 May 2012, heavy rainfall resulting rapid melting of snow and ice from Chorabari Glacier in Kedarnath, India on 16 June 2013, heavy snowfall by Cyclone Hudhud on 13 October 2013 in the Annapurna region, Nepal, and the recent Chamoli flash flood in Uttarakhand in India on 7 February 2021 due to snow, ice, and rock avalanche. Since weather, snow, glacier, and glacial lake monitoring stations are very rare in the Nepal Himalayas, it is very high time to establish such stations across Nepal to reduce and prevent damages caused by glacial hazards in Nepal.
Bajracharya, S. R., Maharjan, S. B., Shrestha, F., Sherpa, T.C., Wagle, N., Shrestha, A. B.
(2020). Inventory of glacial lakes and identification of potentially dangerous glacial lakes in the
Koshi, Gandaki, and Karnali River Basins of Nepal, the Tibet Autonomous Region of China, and
India. Research Report. ICIMOD and UNDP.
ICIMOD (2011). Glacial lakes and glacial lake outburst floods in Nepal. Kathmandu: ICIMOD.
Note: ‘Young Researcher’ Issue 05 – May 2021