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Current Affairs

Flash floods

Date: 11 February 2021 Tags: Miscellaneous

Issue

Flash flood incident in Uttarakhand has provided another warning of the dangers that a Himalayan state like Uttarakhand faces from natural processes like landslides, snow avalanches cloudbursts or lake bursts. 

 

Background

The incident of 2013 showed that such processes can trigger much bigger disasters and cause massive destruction.

 

Details

  • Glaciers are the largest source of freshwater outside of the Polar Regions. Glaciers and snow melt in the Himalayan ecosystem are the source of water for several rivers across the subcontinent.

  • They are responsible for maintaining the perennial supply of water in the river systems like the Indus, Ganges, and Brahmaputra to over a billion people.

 

Glacier shrink

  • Glaciers have reduced considerably in mass and surface area since the little ice age period. Global temperatures began to rise after 1850.

  • They have climbed more rapidly in the 20th century as greenhouse gas levels soared. The rise has been even steeper since the early 1980s.

  • Some models predict that an increase in global temperatures by 2°C from 1850 by 2070 would result in 45% of the medium and large glaciers disappearing completely.

  • Nearly 70% smaller glaciers are likely to melt away. Shrinking glaciers have led to the formation of a large number of glacial lakes all across the Himalayas.

  • Many of these high-altitude lakes are potentially dangerous, because of their potential to cause flash floods in the event of a breach.

  • There has been an increase in the number of such lakes in the last few decades because of an acceleration in the glacial melt.

 

Tackling threat

  • The first step in tackling the threat from these glacial lakes is to start monitoring them and the glaciers more actively and regularly.

  • It is important to get people and measuring instruments on the ground. Relying only on satellites and remote sensing is not going to be enough. 

  • There is a need to closely measure the bathymetric changes, the mechanisms of expansion, changes in water levels, discharge balance, mass balance, and other attributes.

 

Planning

  • The Himalayas are very young mountain systems, and extremely fragile. A minor change in orientation of the rocks can be enough to trigger landslides.

  • It is important to include glaciers in any environment impact assessment for major projects such as construction of dams. The entire catchment areas should be made part of the impact assessment. 

 

Mitigation

  • Several structural and geotechnical measures can be applied to reduce threat from glacial lakes.

  • It is possible to construct channels for gradual and regulated discharge of water from these lakes, which will reduce the pressure on them, and minimise the chances of a breach.

  • Alarm systems can be set up at the lakes, which will warn the community downstream whenever an overflow happens.