Rising temperatures heighten Glacial Lake Outburst Floods , landslide risks in Himalayan region: Glaciologist Randhawa

The Rising temperatures, accelerated glacier retreat and increasing formation of glacial lakes are making the Trans-Himalayan and wider Himalayan region increasingly vulnerable to Glacial Lake Outburst Floods (GLOFs), landslides and flash floods, retired glaciologist and scientist S.S. Randhawa has warned

The rising temperatures, accelerated glacier retreat and increasing formation of glacial lakes are making the Trans-Himalayan and wider Himalayan region increasingly vulnerable to Glacial Lake Outburst Floods (GLOFs), landslides and flash floods, retired glaciologist and scientist S.S. Randhawa has warned, calling for stricter enforcement of building by-laws, restrictions on development in vulnerable areas and scientific mapping of flood-prone zones. Randhawa, former Principal Scientific Officer with the Himachal Pradesh Council for Science, Technology and Environment under the Department of Science and Technology, told ANI that decades of field and satellite-based studies of Himachal Pradesh's glaciers had shown a broad trend of glacier retreat, although the rate of degradation varied considerably between different river basins.

"By and large, most of the glaciers in Himachal Pradesh are in a retreating phase. However, their retreat rates are different because there are several factors involved, including the location of the glacier, its slope, orientation and the amount of winter accumulation," he said. Randhawa said he had been involved in glacier-related research in Himachal Pradesh since joining the Department of Science and Technology in 1993, before retiring in 2023. The work involved both field investigations and satellite-based mapping, with assistance from the Indian Space Research Organisation (ISRO).

He said conventional methods alone were insufficient for studying glaciers in the high-altitude Himalayan terrain because many glacier systems are located in extremely difficult and inaccessible areas. "The Himalayas are also known as the Third Pole after the North and South Poles. To study the large number of glaciers in the Himalayas, glacier mapping work was initiated in Himachal Pradesh in 1993 with the help of ISRO's Space Applications Centre," he said.

According to Randhawa, the initial studies used relatively coarse satellite imagery such as LISS-I and LISS-II, while technological advances have since made much higher-resolution satellite data available. He said earlier studies using LISS-III satellite data, with a resolution of about 23.5 metres, had documented significant deglaciation between 2001 and 2007 across several Himachal basins.

The estimated deglaciation during that period was around 5.18 per cent in the Chenab basin, 7.03 per cent in the Beas basin, 4.67 per cent in the Ravi basin, 6.42 per cent in the Baspa basin and 4.62 per cent in the Spiti basin, he said. Randhawa cautioned that these figures represented basin-specific changes and should not be interpreted as a uniform rate of glacier retreat across the state.

He said rising temperatures were now adding to the pressure on glaciers, particularly in the higher Himalayan areas. "Climate change is taking place and temperatures are increasing. It is also well documented that temperatures in the higher Himalayas are higher compared to low-lying areas. When temperatures rise at higher elevations, the impact on glaciers is greater," he said.

Randhawa said one of the most significant consequences of accelerated glacier melting was the formation and expansion of glacial lakes. When such lakes become unstable and suddenly release large volumes of water, they can trigger GLOFs, causing severe downstream destruction.

He said Himachal Pradesh had witnessed an increase in the number of glacial lakes over time across different river basins, making systematic monitoring essential. Randhawa highlighted detailed monitoring undertaken in the Sutlej basin during his tenure. The basin was monitored annually between April and October using different satellite datasets, including AWiFS, LISS-III and LISS-IV imagery.

He said the LISS-IV data, with a resolution of about 5.8 metres, provided a much more detailed picture. According to the analysis, around 1,359 glacial lakes were identified in the Sutlej basin in 2020. The number rose to 1,632 in 2021, 1,953 in 2022 and 2,292 in 2023.

Of the 2,292 lakes identified in 2023, he said, around 2,192 had an area of less than five hectares, 51 were between five and 10 hectares, and 49 had an area exceeding 10 hectares. The geographical distribution showed around 470 lakes in the Sutlej basin within Himachal, 487 in the Spiti/lower Sutlej region and 1,335 in the Upper Sutlej region on the Tibetan side, according to the study cited by Randhawa.

He said the large number of small lakes was itself an important indicator that changing climatic conditions were affecting the glacial environment. "The number of small lakes is significant. It indicates that the impact of climate change on glaciers is increasing and that lake formation is taking place at a greater scale," he said.

Randhawa said the growing number of glacial lakes should be treated as a long-term disaster-management concern and called for a permanent monitoring mechanism. "All these lakes need to be mapped and monitored every year. We need to establish baseline data and identify changes in their water-spread area and other characteristics," he said.

He stressed that satellite technology would be particularly important because physical access to every glacier and glacial lake was not feasible. "With the help of space technology, whether LISS-IV, LISS-III or better-resolution data available in future, we can study an entire basin at a regional scale," he said.

However, he cautioned that satellite imagery alone could not determine the complete vulnerability of an individual lake. "Field-based data is also required to define the vulnerability of each lake. Because of inaccessible terrain and difficult topographical conditions, it is very difficult to collect detailed field data for every lake. Satellite data can nevertheless provide an initial assessment of changes, area and other characteristics," he said.

Randhawa suggested preparing basin-wise disaster models incorporating glacial lake data, floodplains, low-lying areas and river terraces. He said different GLOF scenarios could then be modelled to determine which downstream areas could potentially be inundated if a particular lake breached.

"Once you have this data, you can undertake basin-level modelling, identify all low-lying areas and floodplains and examine different scenarios. If a particular lake breaches, you can identify which areas are likely to be submerged or impacted and prepare a database accordingly," he said. Such databases, he said, could significantly improve disaster preparedness, evacuation planning and emergency response.

Randhawa said some glacial lakes in the Himalayan region require particularly close monitoring because of their depth, size and connectivity with glaciers. He cited Ghepang Gath Lake as an example of a potentially vulnerable lake, saying its depth, water volume, area and connection with the glacier warranted close scientific monitoring.

He said melting of the connected glacier could contribute to an increase in the lake's water spread. Commenting on the recent glacial flood disaster in Nepal, Randhawa said the exact sequence of events required detailed scientific investigation and that multiple geological and glacial factors could be involved.

Referring to aerial imagery and reports, he said observations appeared to show significant melting around the glacier snout and ablation zone, while changes in river flow and possible blockage of a river course could have contributed to lake formation. He said an earthquake or other geological disturbance could potentially block a river channel, resulting in temporary water accumulation, while the subsequent failure of a hanging glacier or other unstable mass could trigger a sudden release.

Randhawa stressed that such events should not automatically be attributed to a single cause. According to Randhawa, the risk extends across the Himalayan belt and is not confined to Himachal Pradesh.

He identified mountainous regions including Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and other northeastern Himalayan areas as vulnerable to a combination of glacier retreat, glacial lake formation, landslides, flash floods and earthquakes. He said the vulnerability of each basin differed depending on topography, glacier characteristics, climatic conditions and geological factors.

Randhawa also referred to the recent revision of India's seismic zoning framework and said the Himalayan region should be treated as highly vulnerable from an earthquake-risk perspective. He explained that seismic vulnerability is determined on the basis of factors including earthquake epicentres, geological conditions, active thrusts and historical data.

He said earthquakes could also accelerate processes associated with landslides and GLOFs. "Landslides are activated by different types of geological activity. Along thrust zones, landslides can become active, while earthquakes can also trigger slope failures. If a glacial lake already exists, an earthquake or avalanche can potentially disturb it and contribute to a breach," he said.

Randhawa said the increasing climate-induced hazards in mountain regions required a fundamental change in development planning. He called for stricter enforcement of building by-laws and flood regulations, particularly in low-lying areas and along natural river channels.

"We need stricter enforcement. Developmental activity in low-lying areas of every basin should be restricted according to building by-laws and flood regulations," he said. He warned against construction and other activities that interfere with natural river courses.

"If you interfere with the natural nature of a river and carry out developmental activities in its course, the river can change its course at any time. We have seen rivers such as the Beas frequently change their course," he said. He said areas facing greater threats should be identified scientifically and development activity restricted accordingly to reduce future losses.

Randhawa said the most alarming trend was the growing threat from climate-induced hazards in the mountain region. He referred to an increase in temperatures of around 1.6 degrees Celsius in mountain regions, saying higher temperatures were contributing to changes in moisture availability during the summer and monsoon periods.

According to him, increased moisture combined with steep slopes, narrow valleys and complex mountain topography could intensify localised extreme weather events, including cloudbursts. He said areas historically affected by high flood levels should be identified and marked, including through the use of traditional and local knowledge.

"If historical experience shows that water has reached a particular level in the past, that level should be marked so that people do not construct houses up to that level," he suggested. Randhawa welcomed the move towards making geological investigations mandatory for infrastructure development, saying such assessments should be an integral part of planning in mountain regions.

He said geological investigations should apply not only to major infrastructure but also to residential and commercial construction. "Whether it is a house or commercial property, complete geological investigation is necessary to determine whether there is a thrust or other geological instability. If construction is taking place in valley areas, there can also be problems such as liquefaction," he said.

He emphasised that development decisions must take into account geological conditions, flood history, slope stability, river behaviour and climate-related risk Randhawa said climate change could not be stopped through local measures, but the risks could be substantially reduced through better planning, scientific monitoring and strict regulation.

He called for scientific geomorphological mapping of low-lying and vulnerable areas in every river basin to determine where development could safely take place and where it should be restricted. "Climate-induced threats in mountain regions have increased considerably. We need to focus on our planning--where development should take place and where it should not. Every basin needs scientific geomorphological mapping so that vulnerable and non-vulnerable areas can be identified," he said.

He said combining satellite-based glacier and glacial-lake monitoring, field investigations, geological assessments, early-warning systems, historical flood information and strict enforcement of development regulations would be crucial for reducing the impact of future disasters in the Himalayan region. (ANI)