Coastal lifelines, such as water supply and energy infrastructure and evacuation routes, are increasingly vulnerable to higher sea levels and storm surges, inland flooding, erosion, and other climate-related changes.

This finding is from chapter 25 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was a Chapter Lead Authors meeting held in St. Louis, Missouri in April 2012. The key messages were initially developed at this meeting. Key vulnerabilities were operationally defined as those challenges that can fundamentally undermine the functioning of human and natural coastal systems. They arise when these systems are highly exposed and sensitive to climate change and (given present or potential future adaptive capacities) insufficiently prepared or able to respond. The vulnerabilities that the team decided to focus on were informed by ongoing interactions of the author team with coastal managers, planners, and stakeholders, as well as a review of the existing literature. In addition, the author team conducted a thorough review of the technical input reports (TIR) and associated literature, including the coastal zone foundational TIR prepared for the National Climate Assessment (NCA).c9647af9-db7f-4f6a-89bd-2f2293ad26e5 Chapter development was supported by numerous chapter author technical discussions via teleconference from April to June 2012.

Description of evidence base: Coastal infrastructure is defined here to include buildings, roads, railroads, airports, port facilities, subways, tunnels, bridges, water supply systems, wells, sewer lines, pump stations, wastewater treatment plants, water storage and drainage systems, port facilities, energy production and transmission facilities on land and offshore, flood protection systems such as levees and seawalls, and telecommunication equipment. Lifelines are understood in the common usage of that term in hazards management. The key message and supporting text summarize extensive evidence documented in the coastal zone technical input reportfbb1a8af-292f-4fa4-9ed9-2724c65c5f29 207ddc2e-343a-4017-83e1-9ac70c02f723 as well as a technical input report on infrastructure.f0803451-5a89-474a-974f-99c13fdc725d Technical input reports (68) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input, along with the extant scientific literature. Additional evidence is provided in other chapters on hurricanes (Ch. 2: Our Changing Climate, Key Message 8), global sea level rise (Ch. 2: Our Changing Climate, Key Message 10), water supply vulnerabilities (Ch. 3: Water); key coastal transportation vulnerabilities (Ch. 5: Transportation), and energy-related infrastructure (Ch. 4: Energy). This key message focuses mainly on water supply and energy infrastructure and evacuation routes, as these constitute critical lifelines. The evidence base for exposure, sensitivity, and adaptive capacity to higher sea levels and storm surges is very strong, both from empirical observation and historical experience and from studies projecting future impacts on critical coastal infrastructure. There are numerous publications concerning the effects of sea level rise and storm surges on roadways, coastal bridges, and supply of refined products.c9647af9-db7f-4f6a-89bd-2f2293ad26e5 ca601d1d-e05f-4c7c-b5ab-7f35cd27ad57 15fe2aef-6d15-4ea6-a62c-ebb2563d8b4e 8ce65ffc-cdb9-4022-98de-de8bbb141837 6fd7abfe-17d7-49a9-bc90-bf85fa4041d3 ab12aa5f-f335-4633-844f-e0af50715832 78fbf40c-2639-480a-8410-5be748750f2b The information on roadways came from various reports (for example, DOT 2012; Transportation Research Board 20116b4d3283-49dc-4b8d-830b-aa554e37279f 721cfdbb-b8e5-424e-b09d-8ce0b059a431) and other publications (for example, State of Louisiana 2012f1d65fb3-933a-4bbf-b6ac-25ea4d0409d5). The impact on coastal bridges is documented in U.S. Department of Transportation reports.6b4d3283-49dc-4b8d-830b-aa554e37279f a6c54272-7833-4387-a562-229e9e98b233 A number of publications explored the impacts on supply of refined oil-based products such as gasoline.e9bc4af5-c2c2-409a-93d2-b2b6dcdb6528 250d03a2-c6b7-45fb-9585-4e9385aefe2f 85805796-ffa7-4396-bdf4-10a0a3cab671 996f4616-6ae6-4248-9351-f28215ac556c c6da3c06-f7f4-4842-93b0-23f5beb8d67f The evidence base is moderate for the interaction of inland and coastal flooding. There are many and recent publications concerning impacts to wastewater treatment plants3836ed81-4502-4b89-9b27-9fe9ee2d6c42 388a539b-7eb8-48a5-be34-6568a5af8682 5a9e11bc-fdae-474b-a2ad-fe51fa2bb95a and drainage systems.18d757e5-9494-4ca8-9dfe-5cc335c8ffb7 5138b20c-7049-433e-a1ec-24417cccd3c2 8ce65ffc-cdb9-4022-98de-de8bbb141837 a5fd7659-3d17-445f-a924-44a659bb11d1 f03c8590-8b20-442a-a603-dee6c3bf70e1 73596de6-c45e-4dea-b441-fa967b6f658e a13ad871-f5b6-430f-b2d3-cfc1b161e418 These impacts lead to increased risk of urban flooding and disruption of essential services to urban residents.

New information and remaining uncertainties: The projected rate of sea level rise (SLR) is fully accounted for through the use of common scenarios. We note, however, that there is currently limited impacts literature yet that uses the lowest or highest 2100 scenario and none that specifically use the broader range of SLR (0.2 to 2 meters, or 0.7 to 6.6 feet, by 2100) d8089822-678e-4834-a1ec-0dca1da35314 and NCA land-use scenarios (60% to 164% increase in urban and suburban land area).05a757a8-7972-4f33-aed8-424b0afb8fc4 The severity and frequency of storm damage in any given location cannot yet be fully accounted for due to uncertainties in projecting future extratropical and tropical storm frequency, intensity, and changes in storm tracks for different regions (Ch. 2: Our Changing Climate).c9647af9-db7f-4f6a-89bd-2f2293ad26e5 The timely implementation and efficacy of adaptation measures, including planned retreat, in mitigating damages is accounted for in the underlying literature (for example, by varying assumptions about the timing of implementation of adaptation measures and the type of adaptation measures) such as hard protection, elevation, relocation, or protection through wetlands and dunes in front of the infrastructure in question) (for example, Aerts and Botzen 2012; Biging et al. 2012; Bloetscher et al. 2011; Heberger et al. 2009; Irish et al. 2010; Kirshen et al. 201118d757e5-9494-4ca8-9dfe-5cc335c8ffb7 ca601d1d-e05f-4c7c-b5ab-7f35cd27ad57 fc366ced-fcf5-41de-9bd3-cc09c1d33ab6 0fece8dd-1233-4ec3-8958-2944a5b3c967 e378c785-05f0-4f3f-97b1-889eb7e5036d 3836ed81-4502-4b89-9b27-9fe9ee2d6c42). However, such studies can only test the sensitivity of conclusions to these assumptions; they do not allow statements about what is occurring on the ground. Additional uncertainties arise from the confluence of climate change impacts from the inland and ocean side, which have yet to be studied in an integrated fashion across different coastal regions of the United States.

Assessment of confidence based on evidence: Given the evidence base, the large quantity of infrastructure (water-related infrastructure, energy infrastructure, and the 60,000 miles of coastal roads) in the U.S. coastal zone, and the directional trend at least of sea level rise and runoff associated with heavy precipitation events, we have very high confidence that these types of infrastructure in the coastal zone are increasingly vulnerable

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