Climate change adaptation to increasing isk of glacial lake outburst floods : decision making methodology for risk management applied to Imja Lake in Nepal and Lake Palcacocha in Peru

Glacial retreat around the world, accelerated by climate change, has led to the formation of glacier lakes that present a risk of a glacial lake outburst flood (GLOF). GLOFs are sudden, catastrophic events that are impossible to predict. Communities in the path of a potential GLOF are now attempting to implement adaptation projects, yet no quantitative data or guidance is available to understand the benefits of adaptation projects or how to weigh these benefits against the cost of project implementation. The objective of this work is to develop a rational decision making methodology for GLOF risk management that incorporates available scientific information and the uncertainty surrounding the understanding of GLOF events. The decision making methodology consists of 1) identifying flooding scenarios, 2) evaluating the consequences of flooding scenarios, and 3) a nuanced (in terms of the inclusion of intangibles and probabilistic events) economic analysis of flood consequences and adaptation options. The methodology is applied to Lake Palcacocha in Peru and Imja Lake in Nepal to demonstrate the robustness of the methodology in light of different sources of uncertainty and data gaps. For Imja Lake it is concluded that lowering the lake 10 m is the best decision, from an economic standpoint. Nonetheless, the decision is sensitive to changes in the decision tree variables, which should be assessed for accuracy. At Lake Palcacocha it was determined that a GLOF would result in substantial damage to the city of Huaraz and the best decision is to lower the lake 30 m and install an emergency warning system (EWS). This decision is robust to large changes in the uncertain variables.