CHRONIC INUNDATION ALONG THE US COASTLINE: WHERE, WHEN AND HOW TO RESPOND

Sea level rise is contributing to worsening high tide flooding along US coasts. The Union of Concerned Scientists (UCS) conducted a study to identify when and where communities will experience such disruptive flooding as to force difficult, often costly choices. The analysis uses three scenarios of localized sea level rise projections—Highest, Intermediate-high and Intermediate-Low—drawn from the 2014 National Climate Assessment. We identify which communities will face disruptive chronic inundation—defined as locations where 10 percent or more of the usable land area is flooded at least 26 times per year—and when.

We find that, by 2035, about 170 communities will face chronic inundation and possible retreat from affected areas under the intermediate or high scenarios. By 2060, this number jumps to 270 communities under the intermediate scenario and 360 under the high scenario. By the end of the century about 490 communities—including roughly 40 percent of all oceanfront communities on the East and Gulf Coasts—will face chronic inundation and possible retreat with intermediate sea level rise. That number jumps to about 670.

We also used the Social Vulnerability Index, or SoVI, to identify which of the chronically inundated communities might face heightened risks because of additional socioeconomic factors. With the Intermediate-High and Highest sea level rise scenarios, more than half of communities facing effective inundation by 2045 contain areas of current high socioeconomic vulnerability.

Our nation must use the limited window of time before chronic inundation sets in for hundreds of communities, and plan and prepare with a science-based approach that prioritizes equitable outcomes.

This task will be complicated and expensive and it will need to happen on an unprecedented scale for our nation. Socioeconomically vulnerable communities will also need more resources and targeted policies.

A portfolio of actions is needed, including: Halting or phasing out current maladaptive policies and measures; fostering resilience using existing policy frameworks in ambitious ways; and creating and funding bold new policies.

The United States must also work with other nations to cut global warming emissions aggressively to slow the pace of sea level rise and help coastal communities cope with impacts.