12 The Importance of Up-to-Date, and Accurate, Maps In the US, the National Flood Insurance Program (NFIP) is designed to assist owners of property within the 100-year flood zone in rebuilding after a damaging flood. But the maps that FEMA uses for the program—and that many rely on to determine risks—aren’t required to include rainfall hazards, or the often-immense impervious surfaces of cities where rainfall runoff can’t be contained by street gutters. The FEMA maps also rely on hydrologic and hydraulic modeling (of flood peaks and channel capacity) that is often decades out of date, and out of step with dramatic changes to population and the urban landscape. This map visualizes a side-by-side comparison of the spatial distribution of flood depth (right panel) and the spatial distribution of population for non-Hispanic Black, Hispanic, non-Hispanic Asian, and non-Hispanic White populations (left panel). Although the maps cover coastal and river flooding, Sanders said, “They don’t ask, ‘Well, if it rains really hard and the water hits the ground and runs into the streets and it can’t drain fast enough, where’s it going to pond, and who’s it going to flood?’” Even alternative efforts meant to improve on FEMA’s maps don’t properly estimate urban flood risks, says Sanders. Large-scale flood risk models used in nationwide studies offer relatively low accuracy in urban areas, since they typically lack data about urban drainage infrastructure and the condition of flood channels, levees, and dams. They also rely on geographic and computational grids that are too coarse to
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