Improving flood impact estimations

Abstract

A reliable estimation of flood impacts enables meaningful flood risk management and rapid assessments of flood impacts shortly after a flood. The flood in 2021 in Central Europe revealed that these estimations are still inadequate. Therefore, we investigate the influence of different data sets and methods aiming to improve flood impact estimates. We estimated economic flood impacts to private households and companies for a flood event in 2013 in Germany using (a) two different flood maps, (b) two approaches to map exposed objects based on OpenStreetMap (OSM) and the Basic European Asset Map (BEAM), (c) two different approaches to estimate asset values, and (d) tree-based models and Stage-Damage-Functions to describe the vulnerbility. At the macro scale, water masks lead to reasonable impact estimations. At the micro and meso-scale, the identification of affected objects by means of water masks is insufficient leading to unreliable estimations. The choice of exposure data sets is most influential on the estimations. We find that reliable impact estimations are feasible with reported numbers of flood-affected objects from the municipalities. We conclude that more effort should be put in the investigation of different exposure data sets and the estimation of asset values. Furthermore, we recommend the establishment of a reporting system in the municipalities for a fast identification of flood-affected objects shortly after an event.

Flood Vulnerability Models and Household Flood Damage Mitigation Measures: An Econometric Analysis of Survey Data

“…The coefficient of the square root of inundation depth ranges between 0.014 and 0.017 between the models and is significant at the 1% level. This confirms the relationship between inundation depth and flood damage as described in the literature (Sieg & Thieken, 2022;Sultana et al, 2018;Thieken et al, 2005;Wagenaar et al, 2017).…”

“…This approach will not result in a smooth curve but will give a relationship between inundation depth and flood damage. Next, a root function is used to describe the nonlinear effect inundation depth has on flood damage in regression models (Sieg & Thieken, 2022; Sultana et al., 2018; Wagenaar et al., 2017). When estimating the effect of inundation depth and multiple FDM measures, a regression equation in ordinary least squares (OLS) would be as follows: $$${\mathrm{D}\mathrm{a}\mathrm{m}\mathrm{a}\mathrm{g}\mathrm{e}\,\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}}_{i}={\beta }_{0}+{\beta }_{1}\sqrt{{\mathrm{i}\mathrm{n}\mathrm{u}\mathrm{n}\mathrm{d}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\,\mathrm{d}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{h}}_{i}}+{\beta }_{2}{\mathrm{F}\mathrm{D}\mathrm{M}}_{i}+{\beta }_{k}{X}_{i}^{\prime }+{\varepsilon }_{i}$$$ …”

“…This approach will not result in a smooth curve but will give a relationship between inundation depth and flood damage. Next, a root function is used to describe the nonlinear effect inundation depth has on flood damage in regression models (Sieg & Thieken, 2022;Sultana et al, 2018;Wagenaar et al, 2017). When estimating the effect of inundation depth and multiple FDM measures, a regression equation in ordinary least squares (OLS) would be as follows:…”

Toward an adequate level of detail in flood risk assessments

“…However, in these analyses usually model assumptions are varied or artificial variations are introduced (e.g., de Moel et al, 2009; Metin et al, 2018; Winter et al, 2019). Comparisons between different approaches and data sets for each component with different degrees of detail are still rare (Sieg & Thieken, 2022).…”

“…The asset values of buildings and equipment of the companies is estimated based on official statistics from the national accounts (VGR des Bundes) and the German Federal Statistical Office. Content asset values of private households are taken from Paprotny et al (2020), The assets for OSM data are estimated with the unit scaling method following the approach of Sieg and Thieken (2022). These values are compared with the land use based Basic European Asset Map (BEAM as of 2012) (Mueller et al, 2013).…”