Key findings from Bhutan NCAP Project

Submitted by Sukaina Bharwani | published 25th Mar 2011 | last updated 13th Jan 2020

Decadal changes of lakes in the Lunana complex

Decadal changes of lakes in the Lunana complex

Figure 1: Decadal changes in glacial lakes in the Lunana area.

An attempt has been made to map the changes of the glacial lakes in the Lunana area on a decadal base from 1968 to 2001 in terms of both area and length (see figure 1 above).

All the three major lakes (Raphstreng, Thorthormi and Luggye) show a sudden increase in surface area and it is clear that all the lakes except for Raphstreng are still expanding and show an expansion pattern.

Potentially Dangerous Lakes in the Puna Tsang Chu River Basin

24 potentially dangerous lakes were identified during the last inventory work based on a set of criteria such as rise of lake water level, associated mother glacier, condition of dams and topographical features of surroundings. The base maps used for their identification were topographical maps from the 1960s. The Thorthormi Lakes were not significant then as no water bodies were detected on the mother glacier (Thorthormi glacier). But today as shown in the previous section the Thorthormi Lakes are considered to be some of the critically dangerous lakes in the Bhutan Himalayas considering their expansion rate and the unstable moraine dam surrounding it. Therefore, the total number of potentially dangerous lakes in the Bhutan Himalayas at present is 25 with the inclusion of the Thorthormi Lakes.

Out of 25 potentially dangerous lakes, 5 lakes were found at the source of the Mo Chu and 9 lakes were located at the source of the Pho Chu. Therefore a total of 14 potentially dangerous lakes were identified in the Puna Tsang Chu River basin which accounts for 56% of the total potentially dangerous lakes.

Hazard Zones

A hazard is a phenomenon that may adversely affect human life, property, activity or the environment to the extent of causing a disaster. In our context GLOFs from the combination of two potentially dangerous glacial lakes at the source of the Pho Chu are the hazard and we have tried to zone the areas along the Puna Tsang Chu into different levels of hazard from GLOFs. The three hazard zones (red, yellow and blue) identified in this project represent three different hazard levels (high, medium and low) respectively. The technical details and steps involved in the delineation of these different hazard zones are given in the methodology section.

Vulnerability Assessments

Vulnerability can be defined as a condition resulting from physical, social, economic and environmental factors or processes which increase the susceptibility of a community to the impacts of a hazard. The IPCC (1997) defines vulnerability in relation to the impacts of climate change and it 'is the extent to which a natural or social system is susceptible to sustaining damage from climate change'. In our context it is the degree of risk of GLOF along the Puna Tsang Chu on the lives, property and infrastructure located on either side of this river.

Table I: Summary of vulnerability assessments in the project area

Summary of vulnerability assessment in the project area

Vulnerability assessment is a way of establishing who is vulnerable, where they are and what the strategies to combat vulnerability are. It is significant for current and future planning exercises for proper risk management, preparedness and critical decision making which are all essential if the most vulnerable people are to be given the assistance they need. The table above shows the summary of vulnerability assessment in the whole project area. The figure below shows the percentage distribution of different socio-economic assets and infrastructure which falls in different level of hazards if GLOF occurs along the Puna Tsang Chu

Percentage of socio-economic assets and infrastructure in different levels of hazard for the whole project area

Figure 2. Percentage of socio-economic assets and infrastructure in different levels of hazard for the whole project area

The details of individual vulnerable communities and infrastructure are given in the figure above, while the table below shows the areas of different land use in different levels of hazard along the Puna Tsang Chu.

Table II Different land use in different hazard levels in the project area

Different land use in different hazard levels in the project area

 

Percentage of different land use in different hazard levels for the project area

Figure 3. Percentage of different land use in different hazard levels for the project area

Since any kind of flood will have a devastating effect on the land use type along its course it is imperative to make an assessment on the vulnerability of land use along the Puna Tsang Chu for future GLOF scenarios. The figure above shows the percentage of different land use in different hazard levels for the entire area of the project area.

 

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Bhutan NCAP Project

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Methodology of Bhutan NCAP Project

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