Multiscale flood risk assessment under climate change: the case of the Miño River in the city of Ourense, Spain

Abstract. River floods, which are one of the most dangerous natural hazards
worldwide, have increased in intensity and frequency in recent decades as a
result of climate change, and the future scenario is expected to be even
worse. Therefore, their knowledge, predictability, and mitigation represent
a key challenge for the scientific community in the coming decades,
especially in those local areas that are most vulnerable to these extreme
events. In this sense, a multiscale analysis is essential to obtain detailed
maps of the future evolution of floods. In the multiscale analysis, the
historical and future precipitation data from the CORDEX (Coordinated Regional Downscaling Experiment) project are used as
input in a hydrological model (HEC-HMS) which, in turn, feeds a 2D hydraulic
model (Iber+). This integration allows knowing the projected future
changes in the flow pattern of the river, as well as analyzing the impact of
floods in vulnerable areas through the flood hazard maps obtained with
hydraulic simulations. The multiscale analysis is applied to the case of the
Miño-Sil basin (NW Spain), specifically to the city of Ourense. The
results show a delay in the flood season and an increase in the frequency
and intensity of extreme river flows in the Miño-Sil basin, which will
cause more situations of flooding in many areas frequented by pedestrians
and in important infrastructure of the city of Ourense. In addition, an
increase in water depths associated with future floods was also detected,
confirming the trend for future floods to be not only more frequent but also
more intense. Detailed maps of the future evolution of floods also provide
key information to decision-makers to take effective measures in advance in
those areas most vulnerable to flooding in the coming decades. Although the
methodology presented is applied to a particular area, its strength lies in
the fact that its implementation in other basins and cities is simple, also
taking into account that all the models used are freely accessible.
