Connecting global- and local-scale flood risk assessment: a case study of the Rhine River basin flood hazard

This flood hazard study is the first step towards linking global and local scales of flood risk assessment under the International Flood Initiative (IFI) Flagship Project. To simulate river discharges, we utilised a 600-arcsec grid block-wise TOP (BTOP) model to represent the global scale and constructed a local scale 15-arcsec grid BTOP model for the Rhine River basin. Both BTOP models showed similar statistical performances with observed daily river flows, especially for the 1993 and 1995 floods. For both scales, we calculated flood peak discharges using the Gumbel distribution with L-moments in R from the simulated BTOP daily discharges. The obtained flood peak discharges of both scales were comparable with available gauging station records. For the flood inundation simulation, the 600-arcsec flood peaks were disaggregated to the 15-arcsec scale as input to the Flood Inundation Model (FID), and the resulting 15-arcsec FID maps of 10-, 100- and 200-year return periods had similar extents with the existing official flood hazard maps of high, medium and low probability floods, respectively. These preliminary results demonstrate the possibility of obtaining an acceptable flood hazard assessment on a global scale and serve as a starting point for connecting global and local scales of flood risk assessment.