28 Jun 2021

28 Jun 2021

Review status: this preprint is currently under review for the journal NHESS.

Glacial lake outburst flood hazard under current and future conditions: first insights from a transboundary Himalayan basin

Simon Allen1,2, Ashim Sattar1, Owen King3, Guoqing Zhang4,5, Atanu Bhattacharya3,6, Tandong Yao4,5, and Tobias Bolch3 Simon Allen et al.
  • 1Department of Geography, University of Zurich, Zurich, CH-8057, Switzerland
  • 2Institute for Environmental Science, University of Geneva, CH-1205, Geneva
  • 3School of Geography and Sustainable Development, University of St Andrews, St Andrews, KY16 9AL, UK
  • 4Key Laboratory of Tibetan Environmental Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing, China
  • 5CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China
  • 6Department of Remote Sensing & GIS, JIS University, Kolkata 700109, India

Abstract. Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where impacts can be far-reaching. This is particularly true for transboundary Himalayan basins, where risks are expected to further increase as new lakes develop. Given the need for anticipatory approaches to disaster risk reduction, this study aims to demonstrate how the threat from a future lake can be feasibly assessed along-side that of current lakes, and how this information can feed practically into decision-making and response planning. We have focused on two well-known dangerous lakes (Galongco and Jialongco), comparing the consequences of simulated worst-case outburst events from these lakes both in the Tibetan town of Nyalam and downstream at the border with Nepal. In addition, a future scenario has been assessed, whereby an outburst was simulated for a potential new lake forming upstream of Nyalam. Results show that although smallest in size, Jialongco, poses the greatest immediate threat to Nyalam and downstream communities, owing to the high potential for an ice avalanche to trigger an outburst. The future lake scenario would lead to flow depths and velocities that exceed either of the current scenarios, and the peak flood would reach Nepal up to 20 minutes faster. Based on these findings, a comprehensive approach to disaster risk reduction is called for, combining early warning systems with effective land use zoning and capacity building programs. Such approaches address the current drivers of GLOF risk in the basin, while remaining robust in the face of future emerging threats.

Simon Allen et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2021-167', Anonymous Referee #1, 20 Jul 2021
  • RC2: 'Comment on nhess-2021-167', Adam Emmer, 06 Sep 2021
  • RC3: 'Comment on nhess-2021-167', Fabian Walter, 17 Sep 2021

Simon Allen et al.

Simon Allen et al.


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Short summary
This study examines how the formation of a new glacial lake, in response to future glacial melting, could enhance the flood threat to a transboundary basin flowing between Tibet and Nepal. A flood resulting from a catastrophic outburst from this future lake could lead to higher flood levels than currently anticipated, and the flood wave would travel faster. These results can help ensure that hazard mapping and early warning systems in the basin remain robust over future decades.