Can Hydrological Models Be Used to Characterise Spatial Dependency in
Global Stochastic Flood Modelling?
Abstract
Flood models typically produce flood maps with constant return periods
in space, without considering the spatial structure of flood events. At
a large scale, this can lead to a misestimation of flood risk and losses
caused by extreme events. A stochastic approach to global flood
modelling allows the simulation of sets of flood events with realistic
spatial structure that can overcome this problem, but until recently
this has been limited by the availability of gauge data. Previous
research shows that simulated discharge data from global hydrological
models can be used to develop a stochastic flood model of the United
States (Wing et al., 2020) and suggests that the same approach can
potentially be used to build large scale stochastic flood models
elsewhere but this has not so far been tested. This research therefore
focuses on using discharge hindcasts from global hydrological models to
drive stochastic flood models in different areas of the world. By
comparing the outputs of these simulations to a gauge-based approach, we
analyse how a model-based approach can simulate spatial dependency in
large scale flood modelling outside of well-gauged territories such as
the US. Based on data availability we selected different areas in
Australia, South Africa, South America and Europe for the analysis. The
results of this research show that the performance of a model-based
approach in the different continents is promising and the errors are
comparable to the results obtained in the United States by Wing et al.
(2020). In the United States, with this magnitude of errors, the loss
distribution obtained using the model-based approach is near identical
to the one produced by the gauge-based method. This suggests that this
method could be used in other regions to characterize losses. Using a
network of synthetic gauges with data from global hydrological models
would allow the development of a stochastic flood model with detailed
spatial dependency, generating realistic event sets in data-scarce
regions and loss exceedance curves where exposure and vulnerability data
are available.