A global assessment of the societal impacts of glacier outburst floods

Glacier outburst floods are sudden releases of large amounts of water froma glacier. They are a pervasive natural
hazard worldwide. They have an association with climate primarily via glacier mass balance and their impacts on
society partly depend on population pressure and land use. Given the ongoing changes in climate and land use
and population distributions there is therefore an urgent need to discriminate the spatio-temporal patterning
of glacier outburst floods and their impacts. This study presents data compiled from 20 countries and comprising
1348 glacier floods spanning 10 centuries. Societal impactswere assessed using a relative damage index based on
recorded deaths, evacuations, and property and infrastructure destruction and disruption. These floods originated
from332 sites; 70% were fromice-dammed lakes and 36% had recorded societal impact. The number of floods
recorded has apparently reduced since the mid-1990s in all major world regions. Two thirds of sites that have
produced N5 floods (n=32) have floods occurring progressively earlier in the year. Glacier floods have directly
caused at least: 7 deaths in Iceland, 393 deaths in the European Alps, 5745 deaths in South America and 6300
deaths in central Asia. Peru, Nepal and India have experienced fewer floods yet higher levels of damage. One in
five sites in the European Alps has produced floods that have damaged farmland, destroyed homes and damaged
bridges; 10% of sites in South America have produced glacier floods that have killed people and damaged infrastructure;
15% of sites in central Asia have produced floods that have inundated farmland, destroyed homes,
damaged roads and damaged infrastructure. Overall, Bhutan andNepal have the greatest national-level economic
consequences of glacier flood impacts.Werecommend that accurate, full and standardisedmonitoring, recording
and reporting of glacier floods is essential if spatio-temporal patterns in glacier flood occurrence, magnitude and
societal impact are to be better understood. We note that future modelling of the global impact of glacier floods
cannot assume that the same trends will continue and will need to consider combining land-use change with
probability distributions of geomorphological responses to climate change and to human activity.