by Rohan Nath
Climate change is adversely affecting the Indian Himalayan Region (IHR). The disappearance of mountain glaciers and the expansion of large glacial lakes are physical evidence of the dynamic impacts of climate changes in the environment. In addition to the decrease instability of the ice walls and the surrounding rock, the threat from glacial lake outburst floods is increasing over the years. This is further worsened with tourism, residential, and hydropower structure expanding into the mountain regions. Therefore, strategies to diminish the glacial lake outburst flood risk is an urgent requirement.
Glacial lake outburst flood is the sudden discharge of a water reservoir situated underneath, in front, underneath, within, on the surface or at the side of a glacier, and related dam structures can be composed of moraine, ice, or bedrock. The catastrophic failure of moraine dammed lakes often leads to flooding hazard. Large impacts of ice or rock in the Himalayas contribute to over 50% of moraine dam failures.
The triggering potential of glacial lake outburst flood have been integrally modelled and studies are being conducted on quantification of affected land areas, resulting flood paths, and the investigation of the vulnerability of the society due to climate-related disasters and also implement an assessment of glacial lake outburst flood risk across Himachal Pradesh (Fig 1).
The area of study
The study is conducted in the north-western Indian Himalaya in Himachal Pradesh (Table 1).
|Land area||55,000 km2|
|Elevation range||450 to 7000 m above sea level|
|Climate variation||Lower hills – Tropical Middle Himalayan region – Temperate Upper hills – Cold and dry|
Agriculture, hydropower sectors and tourism primarily contribute to the economic growth and employment in the state. There are four hydrological basins in the glaciated area, and all of them flow into the Indus River (Fig. 2).
Risk Assessment and Factors
The mass movements of rock or ice are important factors for assessing the changing potential for glacial lake outburst flood. Parameters such as current glacial lake outburst flood hazard and dam stability which include dam geometry and freeboard height, growth of the lake and associated glacier retreat, the steepness of the lakefront area, permafrost conditions and the vegetation coverage in the dam area are important for assessing the risk associated with moraine-dammed lakes. Extreme hydrometeorological conditions can cause catastrophic glacial lake outburst flood has been well exhibited in the 2013 Kedarnath flood disaster. For ongoing research, the priority should be to constrain the temporal evolution of future lake development.
Two levels of information that can form a firm scientific basis for adaptation planning are:
1. Areas, where communities are most exposed and vulnerable to glacier lake outburst flood, is identified with the help of a standardized risk index.
R = H.V.E
R = Integrated assessment of glacial lake outburst flood risk
H = Physical hazard
V = Vulnerability
E = Exposed People
2. The early anticipation of where new threats is likely to occur over the next few decades is assessed using classified hazard maps which focuses only on the physical threat.
The fluvial terraces and floodplain areas can be a prime site for assessment of loss and damage from glacial lake outburst flood. Vital transportation links and significant agricultural activities concentrated livelihoods and communities face high risk when the glacial lake outburst flood paths converge with main river valleys. The potential frequency of glacial lake outburst flood is likely to increase due to the formation of new lakes because the chances of rock avalanches or falling ice entering into a lake increases leading to a catastrophic overtopping wave.
It is possible to form an improved basis for adaptation planning using the characterization of glacial lake outburst flood exposure where mapped land cover data is available.
Three situations are identified for opportunities for implementation of adaptation strategies:
1. Sites currently threatened by glacial lake outburst floods but no new threats are expected.
2. Sites where new threats are expected.
3. Sites that are currently threatened and new threats are expected to emerge.
The climate risk perspective may be adopted to highlight the interacting social and physical determinants that can cause glacial lake outburst flood events. The disaster can travel long distances, throughout the district, states, as well as national boundaries. Hence, a proper method to identify the risk and predict future challenges is required for the Himalayan region. Few steps can be taken such as increased community awareness and preparedness, early warning systems, and sustainable land use planning to overcome the future challenges regarding glacial lake outburst floods.
1. Allen, S. K., Linsbauer, A., Randhawa, S. S., Huggel, C., Rana, P., & Kumari, A. (2016). Glacial lake outburst flood risk in Himachal Pradesh, India: an integrative and anticipatory approach considering current and future threats. Natural Hazards, 84(3), 1741-1763.