Abstract
AbstractAs urban populations grow, it is increasingly important to accurately characterize flood risk in cities and built up areas. Global digital elevation models (GDEMs) have recently enabled flood risk analysis at broad scale and worldwide, but their accuracy and its impact on modeled flood risk in cities has not been fully investigated. We compare flood extents, hydrographs, depths, and impacts between hydrodynamic simulations, using five spaceborne GDEM products and an airborne LIDAR product. Benchmark observations of a historical flood event in Carlisle (UK) were used to assess the accuracy of each simulation. GDEM simulations are shown to perform significantly less accurately than the airborne LIDAR‐based simulations. No DEM outperforms the others across all metrics; the MERIT DEM is the best predictor of flood extent, but TanDEM‐X performs best for discharge. However, the impacts of flooding from GDEM simulations are consistently overestimated, 2 to 3 times higher than those from LIDAR simulations. Until a high resolution, accurate, global DEM is available, multiple products should be used concurrently to enable the full uncertainty range to be quantified and communicated, to ensure flood risk management decisions are not misinformed.
Highlights
By 2050, approximately 68% of people will live in cities (United Nations Department of Economic and Social Affairs, 2019)
Flood risk assessments for cities produced using Global digital elevation models (GDEMs) should be interpreted with caution as they are likely to overpredict risks
We found variability in the accuracy of models using different GDEMs
Summary
By 2050, approximately 68% of people will live in cities (United Nations Department of Economic and Social Affairs, 2019) Many of these cities are situated in low-lying, flood-prone areas. The lower spatial resolution and vertical accuracy of GDEMs means that their use leads to increased uncertainty. The magnitude of this uncertainty and the differences between GDEM products are only beginning to be explored. When estimated flood hazard zones are used to analyze risks to infrastructure, this uncertainty propagates to damage and loss estimates This propagation is of particular concern when pricing insurance premiums in areas were GDEMs have been used to assess flood risk
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