Effects of digital terrain model uncertainties on high-resolution urban flood damage assessment

This work investigates the impact of high-resolution digital terrain model (DTM) uncertainties on the estimation of urban flood losses. Starting from a Light Detection And Ranging (LiDAR)-derived DTM of an urban area, four digital terrain representations (raw data, building footprints filled, buildings as waterproof blocks, and different elevation data merged) are used to generate a computational mesh to run a 2D flood model for three inundation scenarios, differing in flood volumes. The most detailed DTM is obtained by merging the DTM with elevation points based on a two-step optimal interpolation algorithm. A flood damage model based on stage-damage curves is used to estimate monetary losses to structures at the building scale. Flood maps and flood losses are then compared for each terrain representation. The application of the method to an Italian urban district shows that (a) a significant mismatch between manually surveyed elevation points and DTM can be observed, (b) different sources of elevation data can be merged to obtain an optimal representation of the terrain, (c) in dense urban settlements, important differences in flood extent and losses (up to 180%) occur depending on terrain representation. Considerations on time effort required by the increasing detail of the DTM and on the transferability of the results are presented.