Regional Versus Physically-Based Methods For Flood Inundation Modelling In Data Scarce Areas

Abstract

One of the
main obstacles in mapping flood hazard in data scarce areas is the difficulty
in estimating the design flood, i.e. river discharge corresponding to a given
return period. This exercise can be carried out using regionalization
techniques, which are based on flood data of regions with similar
hydro-climatic conditions, or employing physically based model cascades. In
this context, we compared the flood extents maps derived for a river reach of
the Blue Nile following two alternative methods: i) regional envelope curve
(REC), whereby design floods (e.g. 1-in-20 and 1-in-100 year flood peaks) are
derived from African envelope curves and ii) physical model cascade (PMC),
whereby design floods are calculated from the physical model chain of the
European Centre for Medium-Range Weather Forecasts (ECMWF,). The two design
flood estimates are then used as input of a 2D hydraulic model LISFLOOD-FP and
the simulated flood extents are quantitatively evaluated by comparing to a
reference flood extent model, which uses design floods estimated from in situ
data. The results show the complexity in assessing flood hazard in data scarce
area as PMC largely overestimates the flood extent, while REC underestimates
it.