Impact of modelling scale on probabilistic flood risk assessment: the Malawi case

Abstract

Abstract. In the early months of 2015, destructive floods hit Malawi, causing deaths and economic losses. Flood risk assessment outcomes can be used to increase scientific-supported awareness of risk. The recent increase in availability of high resolution data such as TanDEM-X at 12m resolution makes possible the use of detailed physical based flood hazard models in risk assessment. Nonetheless the scale of hazard modelling still remains an issue, which requires a compromise between level of detail and computational efforts. This work presents two different approaches on hazard modelling. Both methods rely on 32-years of numeric weather re-analysis and rainfall-runoff transformation through a fully distributed WFLOW-type hydrological model. The first method, applied at national scale, uses fast post-processing routines, which estimate flood water depth at a resolution of about 1x1km. The second method applies a full 2D hydraulic model to propagate water discharge into the flood plains and best suites for small areas where assets are concentrated. At the 12m resolution, three hot spots with a model area of approximately 10 x10 km are analysed. Flood hazard maps obtained with both approaches are combined with flood impact models at the same resolution to generate indicators for flood risk. A quantitative comparison of the two approaches is presented in order to show the effects of modelling scale on both hazard and impact losses.

Flood Assessment for Risk-Informed Planning along the Sirba River, Niger

“…The presence of many dwellings in the area exposed to catastrophic flooding, thus of many households, is scantly evidenced in the literature [24,32].…”

Improving flood damage assessments in data-scarce areas by retrieval of building characteristics through UAV image segmentation and machine learning – a case study of the 2019 floods in southern Malawi

“…Corresponding to the building types found in the exposure component of each flood damage assessment, a set of damage curves is created. The description of the different types and their construction material is used to weigh materialspecific damage curves from the CAPRA library, according to the method proposed by Rudari et al (2016). We make use of the expanded aggregation table as proposed by Rudari et al (2016), including the construction material considered for every building type (Table 4).…”

“…The description of the different types and their construction material is used to weigh materialspecific damage curves from the CAPRA library, according to the method proposed by Rudari et al (2016). We make use of the expanded aggregation table as proposed by Rudari et al (2016), including the construction material considered for every building type (Table 4). This table indicates for each building type the building stock material for which CAPRA damage curves are used.…”