Thorthormi lake: Bhutan's impending climate disaster

Mission to reduce chances of glacial lake's outburst fails to achieve target

Published on:

30 Dec 2011, 9:14 am

The Thorthormi glacial lake in northern Bhutan is considered the country's likeliest climate-induced disaster. The lake, perched at a height of more than 4,400 metres, is swelling because of melting ice, and is in danger of bursting its wall. Efforts by the Bhutanese government to lower the lake's water level is yet to eliminate the risk of a disaster, which may sweep away communities living in the upper catchment of the Pho Chu river, fed by the glacier.

It was in 2008 that the Bhutanese government decided to start an operation to reduce the possibility of a glacial lake outburst flood or GLOF (see 'What is glacial lake outburst flood') after Bhutan’s first proposal to artificially lower the Thorthormi lake was accepted under the national adaptation programmes of action (NAPA) in 2006 (see 'Climate adaptation aid to poor countries'). Under the project, supported by the United Nations Development Programme among others, the government aimed to lower the water level of the lake by five metres or 17 million cubic metres of water in four years.

The decision followed a study which showed the lake was expanding and if the lake bursts, it would threaten communities in the Punakha-Wangdue district and Choskhor valley.

The international mission, led by Bhutan's department of geology and mines, to mitigate the risk posed by Thorthormi lake ended in November 2011; the team deputed to accomplish the mission is back after the third and final phase of the project. But the mission is far from accomplished. Operation Thorthormi was delayed by a year and the actual work on it started only in 2009. Since then, the water level in the largest glacial lake in Bhutan, measuring 3.42 sq km was reduced by 3.68m, 1.32m short of the target.

The team members of the mission confirm that Thorthormi lake and other ponds in the Thorthormi glacier are expanding. A past study conducted with old satellite images of the other lakes in the same vicinity showed that annual retreat rate of the glacier is about 30-35 metres each year.

What is glacial lake outburst flood

A glacial lake outburst flood (GLOF) occurs when the dam blocking the glacier's path collapses. The dam may comprise glacier ice or a terminal moraine (eroded material from the sides and bottom of a valley, which the glacier pushes to the front). The collapse may occur due to erosion, build up of water pressure, an avalanche, heavy snow, earthquake, volcanic eruption under the ice, or if a large portion of a glacier breaks off and massively displaces the waters in a glacial lake at its base. When the outburst occurs, water dammed by a glacier or a moraine is released. A water body that is dammed by the front of a glacier is called a marginal lake, and a water body that is capped by the glacier is called a sub-glacial lake.

Glacial lakes may hold millions to hundreds of millions of cubic metres of water. Catastrophic failure of the containing ice or glacial sediment can release this water over a period of minutes or a few days. Peak flows as high as 15,000 cubic metres per second have been recorded in such events, suggesting that the v-shaped canyon of a normally small mountain stream could suddenly develop into an extremely turbulent and fast-moving torrent some 50 metres deep. In a downstream floodplain, the inundation may be somewhat slower, which may spread up to 10 km in width. In either instance, threat to life and property is very high.

Climate adaptation aid to poor countries

The national adaptation programmes of action (NAPAs) under the United Nations Framework Convention on Climate Change (UNFCCC) provides a process for least developed countries (LDCs) to identify priority activities that respond to their urgent and immediate needs to adapt to climate change. NAPAs are action-oriented and country-driven, based on the national circumstances and receive fund support from LDC Funds (LDCF).

LDCF was established under the climate convention decision at the seventh Conference of the Parties (COP) to the UNFCCC, held in October 2001. It is meant to meet the urgent and immediate needs of the LDCs, which are among the most vulnerable and those with less capacity to adapt. The COP requested the Global Environment Fund (GEF) to manage LDCF and to mobilise resources to finance the preparation and the implementation of NAPAs in all such countries.

Persistent danger

Climate Change