Preprints
https://doi.org/10.5194/tc-2020-379
https://doi.org/10.5194/tc-2020-379

  29 Jan 2021

29 Jan 2021

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

The 2020 glacial lake outburst flood at Jinwuco, Tibet: causes, impacts, and implications for hazard and risk assessment

Guoxiong Zheng1,2,3, Martin Mergili4,5, Adam Emmer4, Simon Allen2,6, Anming Bao1,7, Hao Guo8, and Markus Stoffel2,9,10 Guoxiong Zheng et al.
  • 1State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, 830011 Urumqi, China
  • 2Climatic Change Impacts and Risks in the Anthropocene (C-CIA), Institute for Environmental Sciences, University of Geneva, 1205 Geneva, Switzerland
  • 3University of Chinese Academy of Sciences, 100049 Beijing, China
  • 4Institute of Geography and Regional Science, University of Graz, 8010 Graz, Austria
  • 5Institute of Applied Geology, University of Natural Resources and Life Sciences (BOKU), 1190 Vienna, Austria
  • 6Department of Geography, University of Zurich, 8057 Zurich, Switzerland
  • 7China-Pakistan Joint Research Center on Earth Sciences, CAS-HEC, 45320 Islamabad, Pakistan
  • 8School of Geography and Tourism, Qufu Normal University, 276800 Rizhao, China
  • 9Dendrolab.ch, Department of Earth Sciences, University of Geneva, 1205 Geneva, Switzerland
  • 10Department of F.A. Forel for Environmental and Aquatic Sciences, University of Geneva, 1205 Geneva, Switzerland

Abstract. We analyze and reconstruct a recent Glacial Lake Outburst Flood (GLOF) process chain on 26 June 2020, involving the moraine-dammed proglacial lake Jinwuco (30.356° N, 93.631° E) in eastern Nyainqentanglha, Tibet, China. Satellite images reveal that from 1965 to 2020, the surface area of Jinwuco has expanded by 0.2 km2 (+56 %) to 0.56 km2, and subsequently decreased to 0.26 km2 (‒54 %) after the GLOF. Estimates based on topographic reconstruction and sets of published empirical relationships indicate that the GLOF had a volume of 10 million m3, an average breach time of 0.62 hours, and an average peak discharge of 5,390 m3/s at the dam. Based on pre- and post-event high-resolution satellite scenes, we identified a large progressive debris landslide originating from western lateral moraine, having occurred 5–17 days before the GLOF. This landslide was most likely triggered by extremely heavy, south Asian monsoon-associated rainfall in June. The time lag between the landslide and the GLOF suggests that pre-weakening of the dam due to landslide-induced outflow pushed the system towards a tipping point, that was finally exceeded following subsequent rainfall, snowmelt, a secondary landslide, or calving of ice into the lake. We back-calculate part of the GLOF process chain, using the GIS-based open source numerical simulation tool r.avaflow. Two scenarios are considered, assuming a debris landslide-induced impact wave with overtopping and resulting retrogressive erosion of the moraine dam (Scenario A), and retrogressive erosion due to pre-weakening of the dam without a major impact wave (Scenario B). Both scenarios yield plausible results which are in line with empirically derived ranges of peak discharge and breach time. The breaching process is characterized by a slower onset and a resulting delay in Scenario B, compared to Scenario A. Evidence, however, points towards Scenario B as a more realistic possibility. There were no casualties from this GLOF but it caused severe destruction of infrastructure (e.g. roads and bridges) and property losses in downstream areas. Given the clear role of continued glacial retreat in destabilizing the adjacent lateral moraine slopes, and directly enabling the landslide to deposit into the expanding lake body, the GLOF process chain under Scenario B can be robustly attributable to anthropogenic climate change, while downstream consequences have been enhanced by the development of infrastructure on exposed flood plains. Such process chains could become more frequent under a warmer and wetter future climate, calling for comprehensive and forward-looking risk reduction planning.

Guoxiong Zheng et al.

Status: open (until 26 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2020-379', Dmitry Petrakov, 01 Mar 2021 reply
  • RC2: 'Comment on tc-2020-379', Anonymous Referee #2, 01 Mar 2021 reply

Guoxiong Zheng et al.

Guoxiong Zheng et al.

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Short summary
We report on a recent GLOF event that occurred on 26 June 2020 in Tibet, China. We find that unlike most GLOFs in this region that have been typically triggered by an instantaneous ice/rock avalanche into a lake, this event was triggered by an initial landslide from a steep lateral moraine and has a time lag of 5–17 days with the GLOF. This represents an unprecedented case of a complex and gradual process chain, and will provide critical new process understanding on GLOF triggering mechanisms.