TECHNICAL BACKGROUNDER Underwater Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate

The Union of Concerned Scientists used a combination of NOAA elevation data, tide gauge records, and Zillow's ZTRAX database to identify coastal properties at risk of chronic inundation. The analysis defines chronic inundation as areas flooded at least 26 times per year and evaluates three sea-level-rise scenarios: high (6.6 feet), intermediate (4.0 feet), and low (1.6 feet) by the end of the century. Key caveats include the assumption of constant population and demographics, the exclusion of local coastal defenses like sea walls, and the lack of consideration for future adaptation measures.

• The analysis defines the zone of chronic inundation as any area that experiences flooding at least 26 times per year, which averages to once every other week.
• The study utilizes three sea-level-rise scenarios for the end of the century: a high scenario projecting a global average rise of 6.6 feet (2.0 m), an intermediate scenario projecting 4.0 feet (1.2 m), and a low scenario projecting 1.6 feet (0.5 m).
• The low sea-level-rise scenario is used as a proxy for the Paris Agreement, as its projected warming aligns with the goal of keeping temperatures below 3.6°F (2°C) above preindustrial levels.
• To identify at-risk properties, the researchers intersected chronic inundation zones with the Zillow Transaction and Assessment Database (ZTRAX), which provides data on residential and commercial properties.
• The analysis may be conservative because it assumes that population, demographics, and the number of properties remain constant at present-day levels, ignoring future population growth.
• The findings may overestimate flooding in some areas because the elevation data does not capture local coastal defenses such as sea walls or changes to the land like the installation of bulkheads.
• The analysis does not account for future adaptation measures that communities might implement, such as restoring wetlands or building flood-control structures.

APA

Union of Concerned Scientists (2018). TECHNICAL BACKGROUNDER Underwater Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate. https://www.ucs.org/sites/default/files/attach/2018/06/underwater-analysis-technical-backgrounder.pdf

Chicago

Union of Concerned Scientists. TECHNICAL BACKGROUNDER Underwater Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate. 2018. https://www.ucs.org/sites/default/files/attach/2018/06/underwater-analysis-technical-backgrounder.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=TECHNICAL BACKGROUNDER Underwater Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate |date=June 2018 |url=https://www.ucs.org/sites/default/files/attach/2018/06/underwater-analysis-technical-backgrounder.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2018technical, author = {{Union of Concerned Scientists}}, title = {{TECHNICAL BACKGROUNDER Underwater Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate}}, institution = {Union of Concerned Scientists}, year = {2018}, month = jun, url = {https://www.ucs.org/sites/default/files/attach/2018/06/underwater-analysis-technical-backgrounder.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }