Identification of Hazard and Risk for Glacial Lakes in the Nepal Himalaya Using Satellite Imagery from 2000–2015

David Rounce,C Watson,Daene Mckinney

doi:10.3390/rs9070654

Abstract

Glacial lakes in the Nepal Himalaya can threaten downstream communities and have large socio-economic consequences if an outburst flood occurs. This study identified 131 glacial lakes in Nepal in 2015 that are greater than 0.1 km2 and performed a first-pass hazard and risk assessment for each lake. The hazard assessment included mass entering the lake, the moraine stability, and how lake expansion will alter the lake’s hazard in the next 15–30 years. A geometric flood model was used to quantify potential hydropower systems, buildings, agricultural land, and bridges that could be affected by a glacial lake outburst flood. The hazard and downstream impacts were combined to classify the risk associated with each lake. 11 lakes were classified as very high risk and 31 as high risk. The potential flood volume was also estimated and used to prioritize the glacial lakes that are the highest risk, which included Phoksundo Tal, Tsho Rolpa, Chamlang North Tsho, Chamlang South Tsho, and Lumding Tsho. These results are intended to assist stakeholders and decision makers in making well-informed decisions with respect to the glacial lakes that should be the focus of future field studies, modeling efforts, and risk-mitigation actions.

Highlights

The Nepal Himalaya is home to a large number of glacial lakes that can be a serious threat to downstream communities if a glacial lake outburst flood (GLOF) occurs
Nepal appears to be entering a period of time where its government is actively trying to reduce the risk associated with these glacial lakes
This study conducted a holistic assessment of the hazard, downstream impacts, and risk associated with 131 glacial lakes in the Nepal Himalaya that were greater than 0.1 km2, and identified 11 lakes as very high risk and 31 lakes as high risk

Summary

Introduction

The Nepal Himalaya is home to a large number of glacial lakes that can be a serious threat to downstream communities if a glacial lake outburst flood (GLOF) occurs. GLOFs refer to the sudden release of stored lake water, which can have devastating socio-economic consequences, including loss of life, buildings, bridges, transportation routes, arable land, and hydropower systems. In the Himalaya, the main trigger of GLOFs is an avalanche entering a lake, which may cause a tsunami-like wave, that can overtop and erode the terminal moraine, and generate the ensuing flood [1,2,3,4]. Other secondary trigger mechanisms include displacement waves from rockfalls, moraine failure due to dam settlement and/or piping, the degradation of an ice-cored moraine, seismic activity, or the rapid input of water from extreme events or from an outburst flood from a glacial lake located upstream [1,2,3,4,5].

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