Each analysis examined coastal cities with overall populations greater than 20,000. For the first one, we tabulated “at risk” population by overlaying 2010 Census block population counts against FEMA’s 100-year coastal floodplains (Crowell et al 2013) using methods adapted from Strauss et al (2012). FEMA 100-year coastal floodplains factor in storm surge, tides, and waves, and include all areas determined to have an at least one percent annual chance of flooding. Based on locations meeting these criteria and population density, New York City ranked first, with over 245,000 people at risk, followed by Miami and then Pembroke Pines, also in South Florida.

Source: These U.S. Cities Are Most Vulnerable to Major Coastal Flooding and Sea Level Rise | Climate Central