Risk of Chronic Flooding from Sea Level Rise in New York City

Main Findings

Importance of These Findings

Goals of This Analysis

The Data

Data for this analysis are from the Union of Concerned Scientist’s (UCS) Underwater: Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate. Data can be downloaded here. Full details and methodology are described in the Technical Backgrounder. In short, UCS combined data on chronic inundation (defined below) from Dahl et al. 2017 and Spranger-Seigfried et al. 2017 with real estate data from the Zillow Transaction and Assessment Database (ZTRAX). The data were prepared for the entire coastal United States, but only New York City was considered in this analysis.

Defining Chronic Inundation

Chronic inundation is defined as an area that floods at least 26 times per year (i.e., every other week on average).

Sea Level Rise Scenarios Considered

The data prepared by UCS use three sea level rise (SLR) scenarios from the 2014 National Climate Assessment (Parris et al. 2012).

• Low: 1.6 feet (0.5 m) above 1992 levels by 2100. This scenario is a proxy for conditions under the Paris Climate Agreement.
• Intermediate: 4.0 feet (1.2 m) above 1992 levels by 2100
• High: 6.6 feet (2.0 m) above 1992 levels by 2100. This scenario includes rapid ice sheet loss.

Caveats & Limitations

• The data provided by UCS assume static population, building stock, property value, tax rates, etc. in the future. This is certainly not true and will likely lead to an underestimation of risk as most recent trends have shown an increase in development in the floodplain. This might be the most consequential simplification of these data and analysis.

• The data provided by UCS only consider coastal flooding due to sea level rise. Other types of flooding (e.g., riverine, increased precipitation, groundwater, storm surge, etc.) are not included.

• The data provided by UCS do not consider localized coastal defenses such as seawalls or levees. Therefore, flood risk may be overestimated for areas where localized coastal defenses have been or will be pursued.

• From the UCS Technical Backgrounder: “Multi-unit buildings such as apartment complexes were treated such that each unit that can be sold independently was counted as a home. This means that in high-rise apartment buildings, upper story units would be counted as at-risk of chronic inundation even if only the ground floor was flooding.”

Results: 2035 Intermediate Sea Level Rise

Across NYC, a total of 745 homes worth 299.7 M USD and with a population of 1729 are at risk of chronic inundation.

These at risk homes at distributed across 13 zip codes. The following plots show the number of homes by zip code that are at risk due to chronic inundation in 2035 under an intermediate sea level rise scenario. The values above the bars indicate the percentage of homes in the zip code that are at risk.

The top three zip codes with the greatest risk (in terms of population and number of homes) are located in Queens. Manhattan does not have any zip codes with homes at risk of chronic inundation in 2035.

Across NYC, the average price of homes at risk is $401,235.

The following plots show the average home value by zip code that are at risk due to chronic inundation in 2035 under an intermediate sea level rise scenario.

The zip code with the greatest number of homes and population at risk of chronic inundation is XXXX and is located in the XXXX neighborhood.

This table summarizes the data for all zip codes with homes at risk of chronic inundation under an intermediate sea level rise scenario: