Glacial lake outburst floods threaten millions globally

Glacial lake outburst floods (GLOFs) represent a major hazard and can result in significant loss of life. Globally, since 1990, the number and size of glacial lakes has grown rapidly along with downstream population, while socio-economic vulnerability has decreased. Nevertheless, contemporary exposure and vulnerability to GLOFs at the global scale has never been quantified. Here we show that 15 million people globally are exposed to impacts from potential GLOFs. Populations in High Mountains Asia (HMA) are the most exposed and on average live closest to glacial lakes with ~1 million people living within 10 km of a glacial lake. More than half of the globally exposed population are found in just four countries: India, Pakistan, Peru, and China. While HMA has the highest potential for GLOF impacts, it is particularly alarming that the Andes as a region of concern, with similar potential for GLOF impacts to HMA but comparatively few published research studies. Glaciers are particularly sensitive to changes in climate and are highly visible indicators of climate warming. Over the last three decades there have been substantial decreases in global glacier mass, with ice losses between 2006 and 2016 estimated at −332 ± 144 Gt y⁻¹. This decline is likely to persist through the 21st century as most glaciers are at a larger ‘response’ to past climate forcing. In many areas, overdeepening in former glacier beds are uncovered during the course of glacier retreat, which allows melt water to collect as glacial lakes. Glacial lakes can also form via the growth and coalescence of supra-glacial ponds on debris-covered glaciers, and in other ice-marginal settings. The formation of glacial lakes can trigger positive feedbacks, whereby lakes promote further ice loss through calving and subaqueous melting, causing additional melt and retreat, and further ice expansion. Importantly, these lakes can represent a substantial hazard in the form of glacial lake outburst floods (GLOFs). GLOF triggering is complex, with dam breach initiation caused by mass movement-induced impulse waves, lake overfilling due to pluvial, nivial and glacial runoff, and moraine- or ice dam degradation being variably important dependent on setting. Consequently, the probability of a lake releasing a GLOF is difficult to accurately quantify without detailed and localized studies. GLOFs can be highly destructive and can arrive with little prior warning, causing significant damage to property, infrastructure, and agricultural land, and resulting in extensive loss of life. However, the impacts varied significantly across the globe, in the last 70 years, several thousand people have been killed by GLOFs in the Cordillera Blanca of Peru, most from a small number of events, while only 393 deaths in the European Alps can be directly linked to GLOF activity over the last 1000 years. The continued ice loss and expansion of glacial lakes due to climate change therefore represents a globally important natural hazard that requires urgent attention if future loss of life from GLOF is to be minimised and the UN’s Sustainable Development Goals (particularly Goal 11–Disaster Risk Reduction) are not be met. Since 1990, the number, area, and volume of glacial lakes globally has grown rapidly, increasing by 53%, 51%, and 48% respectively. Concurrent with the rapid growth of glacial lakes, many catchments downstream have experienced rapid and large increases in population, infrastructure and hydroelectric power (HEP) schemes, while artisanal culture has intensified. However, the socio-economic vulnerability

Caroline Taylor, Tom R. Robinson, Stuart Dunning, J. Rachel Carr, Matthew Westoby