CASE BOX 2.6 GLACIAL LAKE OUTBURST FLOODS IN BHUTAN

By Rinzin Jamtsho

Background

The landlocked Kingdom of Bhutan is situated near the two Asia superpowers, China and India. Bhutan, which is still developing, nevertheless possesses a dynamic nature that makes itself felt in a variety of ways, ranging from its adop-tion in the 1970s of its own measure of prosperity, Gross Naadop-tional Happiness (GNH), to the unique type of natural disaster it is facing, glacial lake outburst flood (GLOF). A glimpse of Bhutan’s landscape can be found in Figure 2.10.

GLOF is defined as a “flooding due to the outburst of a glacier lake”. A glacier lake outburst flood occurs when a lake – dammed by a glacier or a terminal moraine – fails. The outburst can be triggered by erosion, a critical water pressure, a mass movement, an earthquake or cryoseism. A jökulhlaup is a special type of glacier lake outburst flood related to the outburst of an ice- dammed lake during a volcanic eruption (CRED, 2009). There are a total of 2,674 glacial lakes in Bhutan, of which 562 are associated with glaciers serving as a dam or primary water source at higher altitudes. Due to the effect of cli-mate change, glaciers in the Himalayas are shrinking rapidly and the volume

of water carried by these lakes is increasing at a threatening rate. When the volume of water in the lake exceeds the holding capacity of the dam, whether it is overflowing or breaking down the dam altogether, GLOF occurs. The kingdom’s Department of Geology and Mines has identified 24 glacial lakes as “potentially dangerous lakes” that could pose a GLOF threat to the liveli-hood of people living downstream in the river basins.

Vulnerability: The lack of construction regulations render physical infra-structures in both private and public domains susceptible to hazard. The lack of settlement regulation that prevents people from residing in hazard- prone districts and the dependency of people on agriculture and forestry products mean more and more people are becoming exposed. The destabilisation of slopes, primarily due to human activities, makes landslides or mudslides an additional hazard in a GLOF. The geographical location of Bhutan within the seismic zone means the chance of earthquake compounds the risk of the haz-ard. The lack of medical facilities and inaccessibility to communication net-works and transportation systems further render the population vulnerable.

Hazard: The volume of water in glacial lakes is expanding quickly and some have been identified as “potentially dangerous lakes” which are at risk of releasing water.

Exposure: There are communities living downstream in the river basins of the lakes, as well as agriculture, industrial and other economic activities that take place along the way.

FIGURE 2.10 Landscape of Bhutan Source: Photo by CCOUC. All rights reserved.

Disaster Risk Index (DRI)

Disaster Risk Index (DRI) is a calculation of the average risk of death per country in large- and medium- scale disasters associated with earthquakes, tropical cyclones, droughts and fl oods, based on data from 1980 to 2000. The components included in the DRI are hazard, physical exposure and vulnerability (United Nations Devel-opment Programme [UNDP], 2004). Physical exposure is the number of people in a country (in absolute terms) or the frequency of a hazard event per million people (in relative terms). Vulnerability refers to various social, economic, cultural, political and physical variables that make people more or less able to recover from the hazard event. In DRI, “risk” exclusively refers to the risk of death in disaster, and does not include the risk of damage to livelihoods and the economy, due to the limited data available from all countries. As emphasised in its defi nition, DRI measures only the medium- and large- scale disasters, defi ned as at least ten deaths, 100 affected people and/or a call for international assistance.

A sample of how the Disaster Risk Indices worldwide may be illustrated is shown in Figure 2.11 . According to the DRI, Southeast and Southwest Asia face the highest and experience the most consistent disaster risk across regions, followed by Africa and Latin America. Northern America, Europe and Eastern Europe face the lowest risk.

In summary, a natural hazard will not become a disaster unless people are vulner-able and exposed to it. The degree of impact depends on people’s vulnerability – that is the extent to which a community, structure, service or geographic area is likely to be damaged or disrupted by the impact of a particular hazard. This impact can also be mitigated by the manageability, or coping capacity , of the population, which often refers to the organisational response to the hazard and the ability of the popula-tion to respond. The foregoing equapopula-tion indicates that in order to reduce risk, hazard, exposure and vulnerability must be reduced while manageability must be increased.

Manageability: The setting up of a designated Disaster Mitigation, Pre-vention and Preparedness Budget by the Royal Government of Bhutan, the establishment of a warning system with regular testing, and the education and training of officials, intervention teams and multidisciplinary teams across public and private sectors all build up the manageability against disasters.

Risk: GLOF took place in Bhutan in 1957, 1960 and most recently in 1994.

The 1994 GLOF event damaged more than 1,700 acres of agricultural land and a dozen houses and washed away five water mills and 16 yaks. A total of 16 tonnes of foodgrain were destroyed by the incident (Royal Government of Bhutan Ministry of Home and Cultural Affairs, Department of Local Gov-ernance, Disaster Management Division, 2006; Royal Government of Bhutan National Environment Commission, 2006).

FIGURE 2.11 Disaster Risk Index (DRI)

Source: Adapted from Peduzzi, Dao, Herold, and Mouton (2009).

KNOWLEDGE BOX 2.3 WORLD ATLAS OF NATURAL