21 February 2023

‘Millions’ in India, Pakistan at risk of flooding from glacial lakes: What a new study says

GS-1: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.

A new study‘Glacial lake outburst floods threaten millions globally’published in in the journal ‘Nature’warns that about 15 million people worldwide are at risk of sudden and deadly flooding from expanding glacial lakes caused by global warming. India, Pakistan, Peru, and China are the countries with more than half of the people who could be affected. 

Shrinking glaciers lead to the formation of glacial lakes, and when the water is released, it causes flooding downstream, known as glacial lake outburst floods (GLOFs).

The risk of GLOFs has multiplied due to climate change, though they have been occurring since the ice age. According to a study from 2020, the number and total area of glacial lakes worldwide have increased by roughly 50% since 1990.

Glacial Lake Outburst Floods (GLOFs)

• Glacial lakes, which are bodies of water located in front of, on top of, or beneath a melting glacier, become increasingly hazardous as they grow in size. This is due to the fact that these lakes are often dammed by unstable ice or sediment made up of loose rock and debris.
• If the boundary holding them in place were to break, large volumes of water would rapidly flow down the side of mountains, resulting in flooding in areas downstream. 
• This phenomenon is known as glacial lake outburst floods(GLOFs).
• Glacial lakes are frequently located in rugged, mountainous areas, making them vulnerable to landslides or ice avalanches that can fall directly into the lakes. This can result in the displacement of water, causing it to overflow the natural dam and flood downstream areas.
• GLOFs can cause massive destruction of property, infrastructure, and agricultural land, as well as the loss of hundreds of lives, as they often occur with little warning.

• For example, the flash floods and GLOF triggered by the Chorabari Tal glacial lake in Uttarakhand's Kedarnath in 2013 caused the deaths of thousands of people.

Features of GLOFs

• GLOFs are characterized by three primary features: 
• Sudden water releases 
• Rapid events lasting from hours to days, and 
• Large downstream river discharges. 
• The most severe GLOFs have caused significant landscape changes and affected regional climates by releasing enormous amounts of freshwater into the oceans.

Causes of GLOFs

• Rapid slope movement into the lake
• Heavy rainfall/snowmelt
• Cascade effects triggered by floods from an upstream lake
• Ice avalanches
• Earthquakes
• Melting of ice incorporated in dam/forming the dam
• Obstruction of subsurface outflow tunnels
• Long-term dam degradation

Rising Temperatures Increase Risk of Dangerous Glacial Lakes

• As global temperatures continue to rise, there is a growing risk of larger and more numerous glacial lakes forming due to glacier retreat. 
• Additionally, these lakes may be increasingly exposed to potential triggers, such as large landslides or ice avalanches that can cause the natural dam holding the lake to fail and result in GLOFs.
• As a result, lakes that may not currently pose a threat could become a concern in the future, and new, potentially dangerous lakes may form. 

Findings of the Study on Glacial Lake Outburst Floods (GLOFs)

• Researchers used satellite-derived data and population metrics to identify the areas and communities most in danger from GLOFs.
• Around 15 million people across the world are at risk of sudden and deadly flooding from glacial lakes that are expanding and increasing in numbers due to global warming.
• Populations in High Mountains Asia (HMA) are the most exposed, with around one million people living within 10 km of a glacial lake.
• India and Pakistan make up one-third of the total number of people globally exposed to GLOFs, with around three million people in India and around two million people in Pakistan.
• Social vulnerability is a key factor in glacial flood risks in addition to the size and number of glacial lakes in an area.
• The most dangerous catchment in the world is Khyber Pakhtunkhwa in Pakistan.
• Areas with a large number of glacial lakes like Greenland and Canada have very few people vulnerable to GLOFs due to low population and corruption levels.
• Peru ranks third globally in danger levels, with glacial lakes across the Andes increasing by 93% in the past two decades due to climate change.

Way Forward

• Preventing GLOFs is a complex issue and requires multiple solutions.
• Limiting climate change and keeping warming under 1.5 degree Celsius is crucial to slow the growth of glacial lakes.
• Even if all emissions are stopped today, GLOF hazards will continue to increase for several decades due to the ice loss that is already 'locked in'.
• Effective measures need to be taken by working with national and regional governments as well as communities themselves.
• Local-level efforts should be made to find appropriate measures to protect threatened populations.

[Ref- IE]

Fact File