Validation of a 30 m resolution flood hazard model of the conterminous United States

Abstract

This paper reports the development of a ∼30 m resolution two‐dimensional hydrodynamic model of the conterminous U.S. using only publicly available data. The model employs a highly efficient numerical solution of the local inertial form of the shallow water equations which simulates fluvial flooding in catchments down to 50 km2 and pluvial flooding in all catchments. Importantly, we use the U.S. Geological Survey (USGS) National Elevation Dataset to determine topography; the U.S. Army Corps of Engineers National Levee Database to explicitly represent known flood defenses; and global regionalized flood frequency analysis to characterize return period flows and rainfalls. We validate these simulations against the complete catalogue of Federal Emergency Management Agency (FEMA) Special Flood Hazard Area (SFHA) maps and detailed local hydraulic models developed by the USGS. Where the FEMA SFHAs are based on high‐quality local models, the continental‐scale model attains a hit rate of 86%. This correspondence improves in temperate areas and for basins above 400 km2. Against the higher quality USGS data, the average hit rate reaches 92% for the 1 in 100 year flood, and 90% for all flood return periods. Given typical hydraulic modeling uncertainties in the FEMA maps and USGS model outputs (e.g., errors in estimating return period flows), it is probable that the continental‐scale model can replicate both to within error. The results show that continental‐scale models may now offer sufficient rigor to inform some decision‐making needs with dramatically lower cost and greater coverage than approaches based on a patchwork of local studies.

Estimates of present and future flood risk in the conterminous United States

“…These layers are of significantly higher quality and spatial coverage than those that have previously informed exposure and risk estimations. Validation of the new hazard layers [16] suggests they are of commensurate quality to local studies carried out by US government agencies. These new high-resolution analyses with a realistic representation of flood physics indicate that the population exposed to serious flooding in CONUS is 2.6-3.1 times higher than previous estimates.…”

High‐Resolution Land Surface Modeling of Hydrological Changes Over the Sanjiangyuan Region in the Eastern Tibetan Plateau: 1. Model Development and Evaluation

“…Through five decades of development, LSMs have been augmented from simple bucket models (Manabe, ) to comprehensive Earth system models that simulate water cycle, energy cycle, carbon cycle, and even nutrient cycle (Oleson et al, ; Tian et al, ). Besides developing a very complicated system that is expected to consider as many biogeophysical and biogeochemical processes as possible, another direction is to make LSMs useful for applications (Wood et al, ), for example, water resources management (Wada et al, ), flood/drought early warning (Wing et al, ), and detection and attribution of hydrological changes (Yuan et al, ). The latter direction requires developing high‐resolution LSMs that can provide locally relevant information (Bierkens et al, ).…”

Collaborative Modeling With Fine‐Resolution Data Enhances Flood Awareness, Minimizes Differences in Flood Perception, and Produces Actionable Flood Maps

“…Additionally, flood maps depicting historical flooding events are advantageous for productive, nontechnical dialogue aimed at reducing flood vulnerabilities. Collaborative flood modeling aligns with the strategic plans of FEMA to support local leadership of FRM, creating a process for local stakeholders to contemplate flooding, map risks in ways that align with local decision‐making needs, and enhance deliberations over strategies and projects to manage risks. It can be thought of as a bottom‐up alternative to what has become a top‐down process of flood hazard mapping that is limiting important dialogue about flooding (Soden et al, ) and prone to significant errors (NRC 2009, Wing et al, , NASEM 2019).…”

“…Damages have been escalating for decades (Cartwright, 2005;Hinkel et al, 2014;Jongman et al, 2012;Sundermann et al, 2014), and a U.S. record was set in 2017 with over $300 billion in disaster losses, mainly from hurricanes and flooding (National Oceanic and Atmospheric Administration, 2018). Cities around the world (Hanson et al, 2011, Hinkel et al, 2014, Kron, 2013 and municipalities across the United States (Kulp & Strauss, 2017) are threatened by coastal flooding, and nearly 41 million Americans live within 100-year flood zones associated with fluvial and pluvial flooding (Wing et al, 2017). Gall et al (2011) report that flood losses in the United States are not just growing in an absolute sense, after adjusting for inflation, but on a per capita basis and suggest that impacts are even greater than reported because of inadequate monitoring and assessment.…”