  While a social event, such as a concert or a food festival, is a common
experience to people, a natural disaster is experienced by a fewer individuals.
The ordinary and common ground experience of social events could be therefore
used to better understand the complex impacts of uncommon, but devastating
natural events on society, such as floods. Based on this idea, we present a
comparison - in terms of human mobility -, between an extreme local flood that
occurred in 2017 in Switzerland, and social events which took place in the same
region, in the weeks before and after the inundation. Using mobile phone
location data, we show that the severe local flood and social events have a
similar impact on human mobility, both at the national scale and at a local
scale. At the national level, we found a small difference between the
distributions of visitors and their travelled distances among the several weeks
in which the events took place. At the local level, instead, we detected the
anomalies (in time series) in the number of people travelling each road and
railway, and we found that the distributions of anomalies, and of their
clusters, are comparable between the flood and the social events. Hence, our
findings suggest that the knowledge on ubiquitous social events can be employed
to characterise the impacts of rare natural disasters on human mobility. The
proposed methods at the local level can thus be used to analyse the
disturbances in complex spatial networks and, in general, as complementary
approaches for the analyses of complex systems.
