Abstract
Glacial retreat causes the formation of glacier lakes with the potential of producing glacial lake outburst floods (GLOFs). Imja Lake in Nepal is considered at risk for a GLOF. Communities in the path of a potential Imja GLOF are implementing adaptation projects, yet no quantitative data or guidance is available to understand the benefits of these projects or how to weigh benefits against the cost of implementation. We develop and demonstrate a decision-making methodology for GLOF risk management, incorporating available scientific information and uncertainty. The methodology consists of (1) identifying flooding scenarios, (2) evaluating scenario consequences, and (3) performing an economic analysis of proposed adaptation projects. The methodology is applied to assess benefits in Dingboche of lowering Imja Lake by 3, 10 and 20 m. The results show that the baseline case (no lake lowering) has the lowest expected cost because of low valuation of agricultural land and homes in the literature. Nonetheless, the result is sensitive to changes in the analysis variables. We also found that lowering the lake by 10 or 20 m is efficient according only to the methodology used here; however, considering only direct economic damages and literature cost estimates, the costs outweigh the benefits for these projects.
Highlights
High altitude glaciated regions have experienced glacial retreat since the end of the Little IceAge [1,2]
Modeling was not conducted further downstream because digital elevation models of sufficient resolution were not available further downstream at the time the study was conducted [18]. The results of this analysis are incomplete for decision making purposes as the full extent of the damage from an Imja glacial lake outburst floods (GLOFs) has not been quantified
The decision analysis (DA) methodology allowed for the comparison of proposed projects considering uncertainty in the timing and likelihood of a GLOF
Summary
High altitude glaciated regions have experienced glacial retreat since the end of the Little Ice. To predict a future GLOF, researchers must model the triggering mechanism, possible moraine erosion and breach, and downstream inundation through often poorly surveyed valleys [9,12,14,15,16] These difficulties have led researchers to rely on simplified models and approximations to overcome high complexity and lack of data [12]. The risk management methodology presented here and applied to Imja Lake in Nepal consists of a series of analytical procedures meant to quantitatively include the existing knowledge regarding GLOF risks, reflect the uncertainty regarding the occurrence, timing, and characteristics of a flood, and allow for incorporation of stakeholder concerns Through this analytical framework, we seek to understand the costs and benefits of GLOF risk mitigation works and provide information to help guide decision makers as they consider the various options. This method could be useful for decision makers in other countries facing GLOF mitigation needs
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