Estimating the United States population at risk from coastal flood-related hazards

Abstract

Over the past couple of decades a number of papers have been published that provide estimates of United States population living in coastal areas. These estimates vary widely; ranging from less than 5%, to more than 50% of the U.S. population living in coastal areas. The reason for the wide range in estimates is that there are a variety of criteria that can be combined in a number of permutations to define “coastal areas.” For example, coastal areas may be defined based on probability of coastal flooding, inundation caused by future changes in sea levels, or simply by proximity to the coastline itself. In addition, spatial buffers, such as geopolitical units (e.g., counties and census block groups), or prescribed distances (e.g., 50- or 100-mile distance buffers), can also be used to provide a measure of uncertainty associated with economic exposure, or with measurement error. Other types and categories of defining criteria can be used to further characterize coastal areas. In this chapter we focused our attention on estimating U.S. population at risk from the 1% annual chance coastal flood. The 1% annual chance flood (both coastal and riverine) is used by FEMA in the administration of the National Flood Insurance Program (NFIP). The methods used in this analysis followed those of Crowell et al. (J Coast Res 26:201–211, 2010) who used a three-step process to determine coastal population: (1) create a national digital flood hazard database using FEMA (or FEMA-derived) datasets; (2) use a systematic method to separate coastal from riverine flood hazard areas; and (3) combine 2010 census block group data (assuming uniform population distribution) with the digital coastal flood hazard database using a geographic information system. The results of this analysis indicate that approximately 2.8% of the U.S. population lives in areas directly subject to 1% chance coastal flood. In addition, a total of 395 counties were found to be contiguous with the ocean or Great Lakes coast and/or have at least some coastal flood hazard areas (as based on the 1% annual chance coastal flood) located within their boundaries. About 39% of the U.S. population lives in these “coastal” counties.