Using scenario-based stress testing to identify medium (2050) and long-term (2100) sea level rise risks
This project uses a qualitative, scenario-based stress testing approach to identify U.S. coastal census tracts that are expected to be negatively affected by medium (2050) and long-term sea level rise (SLR). (2100). A baseline scenario and two “plausible but severe” adverse scenarios covering between 1 and 7 feet of sea level rise were designed.
Key observations throughout this analysis were that outside of FEMA's current high-risk areas, there are ~3,500 other census tracts along the contiguous US coast expected to experience an average SLR increase of 1 foot in the medium term (by 2050). In the longer term (by 2100), ~1,660 additional census tracts are at risk of 2 to 7 feet of SLR. Observations for the medium term are particularly important given that they are expected to materialize inconsiderate of future emissions trajectories or other climate mitigation actions due to ocean warming that has already occurred due to climate changetech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³.
This project predominantly uses Python data analysis libraries, e.g. pandas and geopandas, as well as some visualization libraries, e.g. matplotlib, seaborn. The code for this project can be found. here. Data for this project comes primarily from the US Census Bureau and NOAA. More details can be found in the technology and Data section below.
Why coastal real estate and sea level rise?
About 40% of the US population, or ~128 million people, reside in coastal counties.¹. While residential assets in general have been affected by a number of extreme weather events in recent years, e.g. hurricanes, wildfires, etc., for these coastal residents, another major emerging risk is flooding and property loss. properties due to accelerated sea level rise (SLR). . However, in this project's exploratory research, it was discovered that there may not yet be a deep understanding of the full extent of the potential impacts of SLR. Therefore, this project aims to raise awareness in the regions that are expected to be affected in the medium term (2050) and long term (2100) in various scenarios of accelerated sea level rise.
The National Oceanic and Atmospheric Administration (NOAA) is a major American scientific agency charged with monitoring ocean and atmospheric conditions.². According to NOAA's 2022 sea level rise technical reporttech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³sea level is currently rising at a rate significantly accelerated pace compared to levels observed earlier in the 20th century: Sea levels along the contiguous US coast are expected to rise, on average, both in the next 30 years (2020-2050) and in the last 100 years (1920-2020).
In the long term (to 2100), SLR projections along the contiguous US coast vary between 2 and 7 feet on average compared to 2000 levels. The variability in these projections is primarily due to the uncertainty about future greenhouse gas emission rates and resulting global warming, which is the key driver for the SLR. In the medium term (by 2050), given the warming of the ocean that has already occurred due to climate changetech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³Sea levels along the contiguous US coasts are expected to rise between 1.3 and 2 feet on average, inconsiderate of future emissions trajectories or other climate change mitigation measures. Additionally, these higher sea levels are also expected to cause more high tide flooding (HTF) events than occur today: minor disruptive HTF events are projected to increase from 3 events/year in 2020 to >10 events/year by 2050, and large destructive events HTF events are projected to increase from 0.04 events/year in 2020 to 0.2 events/year in 2050).
Project objectives
In light of these projections of coastal sea level rise for the contiguous United States, the objectives of this project are twofold:
- Provide the general public (potential home buyers, mortgage lenders, etc.) with a tool to visualize the regional impacts of SLR in the medium term (2050) and long term (2100). Sea level rise is studied at various intensities ranging from 1 foot to 7 feet.
- Provide specific information (FIPS codes) about the census tracts that would be affected in each SLR severity scenario. Home buyers and mortgage lenders can then factor this census tract-level location information into their purchasing decisions to access what haircut, if any, they would like to apply to their property value assessment.
Scenario-based approach to assess long-term SLR impacts
In the long term, given the potential variability in SLR projections, this project has been designed as a qualitative, scenario-based stress test. The SLR scenarios have been designed based on the principles used in the Federal Reserve's capital stress testing exercise.⁴; One baseline scenario and two “plausible but severe” SLR scenarios have been used to evaluate how various coastal counties/census tracts within the contiguous United States may be affected at various levels of SLR over the long term.
The specific SLR levels chosen for each of these scenarios were based on the 2022 NOAA SLR Technical Report.tech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³. In particular, three long-term levels of NOAA SLR are considered in this project: Low (0.6 m or approximately 2 feet), Intermediate (1.2 m or approximately 4 feet), and High (2.2 m or approximately 7 feet); These projected SLR levels have been assigned to the qualitative stress testing scenarios as shown below:
- A baseline scenario in which sea level is projected to rise by 2 feet
- An adverse scenario in which sea level is projected to rise by 4 feet
- A severely adverse scenario where sea level is projected to rise by 7 feet
The reference scenario maps to NOAA's long-term “low” SLR projection of approximately 2 feet. This low projection is expected to materialize even at low emissions levels with >92% certainty at all levels of global temperature rise.tech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>3. Adverse and seriously adverse scenarios must be “plausible but serious.” NOAA's low-term “intermediate” SLR of approximately 4 feet and “high” SLR of approximately 7 feet have been considered for the adverse and severely adverse scenarios, respectively. These high SLRs are associated with higher greenhouse gas emissions and correspondingly larger increases in global temperatures compared to pre-industrial levels. Extreme SLR scenarios greater than 2.5 m (approximately 8 ft) are no longer considered plausible by 2100tech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³ and therefore, the maximum SLR level considered in this project is NOAA's “plausible but severe” high SLR of 7 feet for the severely adverse scenario.
Additional analysis for the medium term
In addition to the long-term impacts of SLR, this project also analyzes census tracts expected to be affected by SLR in the medium term (2050). In the medium term, SLR is limited at the low end by 1 foot and at the high end by 2 feet for the contiguous United States. Recent scientific advances have led to a better understanding of the factors driving SLR and therefore there is much more confidence in this narrower range (regardless of the future course of emission trajectories).tech-report-sections.html” rel=”noopener ugc nofollow” target=”_blank”>³. Because of this increased confidence in medium-term SLR predictions, this project does not use a scenario-based approach for the medium term. Instead, all contiguous US coastal census tracts at risk of 1 foot SLR by 2050 are considered at risk in the medium term in this project.
Analysis of current risks versus emerging risks
This project analyzed 20 coastal states in the contiguous United States, covering ~200 coastal counties and ~22,000 coastal census tracts within them. Each census tract was analyzed in terms of whether it is currently known to be at risk, i.e., “current risk regions,” versus whether it could be at risk in the medium- and long-term future, i.e., “emerging risk regions.” ”. ”.
The first part of the project involved understanding the current risks. In terms of sea level rise, one of the simplest ways it could manifest itself would be flooding. The Federal Emergency Management Agency (FEMA) has identified regions at high risk of flooding (FEMA floodplains)⁵ . This project used FEMA high-risk floodplains as an indicator of areas currently known to be at risk for coastal flooding. In this project, these regions are considered “current risk regions.”
The second part of this project delved into identifying census areas that may be at risk in the medium or long term. This project leveraged NOAA sea level rise information to identify census tracts that could become an emerging risk in the medium term (2050) or long term (2100), i.e. “emerging risk regions.” To better understand the severity of the risk from sea level rise, the emerging risk was divided into four categories: one category covering the medium term* and three categories based on longer-term scenarios:
- Emerging medium-term risk (1 foot SLR by 2050)
- Emerging long-term risk in the base case (2 ft SLR by 2100)
- Emerging long-term risk in an adverse scenario (4 ft SLR by 2100)
- Emerging long-term risk in Sev. Adverse scenario (7ft SLR for 2100)
*since there is more confidence in SLR predictions, no medium-term scenario-based approach is needed.
Key observations
Key observations through this analysis were that outside of the current FEMA high-risk areas, there are ~3,500 other census tracts along the contiguous US coast that are expected to experience an average increase in SLR of 1 foot in the medium term (by 2050) and longer. In the long term (by 2100), ~1,660 additional census tracts are at risk of having between 2 and 7 feet of SLR.
