Due to sea level rise (SLR), coastal storms and high tides have amplified coastal flooding and erosion impacts, and this trend will continue into the future, with some regions more vulnerable than others (Ch. 2: Climate, KM 9).6,7,8,9,36,37,38 High tide flooding is already forcing some East Coast cities to install costly pump stations to frequently clear floodwaters from the streets (such as Miami Beach, as shown in Figure 8.3) (see also Ch. 19: Southeast, KM 2) and to mobilize emergency responders to routinely close flooded streets. Along with increases in tidally driven flooding, storm surges are higher due to SLR.36,39,40 Warmer air temperatures have increased the probability of heavy precipitation events,41,42,43 permafrost thawing, and earlier season sea ice loss, leading to increased erosion over significant miles of coastline (Ch. 26: Alaska, KM 2). The severity of compound events—the coupling of surge, discharge from rivers, and heavy precipitation—has increased in many coastal cities (Ch. 19: Southeast, KM 2; Ch. 3: Water, KM 2).18,19 In addition, modeling suggests that tropical cyclone intensity will increase,40,44,45 which would lead to greater damage upon landfall. Collectively, these factors already threaten coastal economies, public safety, and well-being, and continued growth and development along the coast increase the risk to more people and infrastructure.
Even under a very low scenario (RCP2.6) (see the Scenario Products section of App. 3 for more on scenarios), projections indicate that the frequency, depth, and extent of both high tide and more severe, damaging coastal flooding will increase rapidly in the coming decades.7,8,36,46,47,48 With rapid ice loss from Greenland and Antarctica under the higher scenario (RCP8.5), an Extreme scenario of global sea level rising upwards of 8 feet by 2100 is a possibility.36,37,49,50,51,52 Under this rise, the average daily high tide would exceed the current 100-year (1% annual chance) coastal water level event in most U.S. coastal locations.8,39,53 Because these low-probability, high-consequence risks cannot be ruled out, a robust risk management approach to future planning would involve their consideration.
Coastal property owners are likely to bear costs from SLR and storm surge, including those associated with property abandonment; residual storm damages; protective adaptation measures, such as property elevation; beach nourishment; and shoreline armoring.35 The potential for future losses is great, with continued and often expensive development at the coasts increasing exposure (Ch. 5: Land Changes, KM 2).54,55 Shoreline counties hold 49.4 million housing units, while homes and businesses worth at least $1.4 trillion sit within about 1/8th mile of the coast.56 Flooding from rising sea levels and storms is likely to destroy, or make unsuitable for use, billions of dollars of property by the middle of this century, with the Atlantic and Gulf coasts facing greater-than-average risk compared to other regions of the country.57,58,59 Recent economic analysis finds that under a higher scenario (RCP8.5), it is likely (a 66% probability, which corresponds to the Intermediate-Low to Intermediate sea level rise scenarios) that between $66 billion and $106 billion worth of real estate will be below sea level by 2050; and $238 billion to $507 billion, by 2100.60
These market impacts have the potential to influence property developers, lenders, servicers, mortgage insurers, and the mortgage-backed securities industry.58,61 Coastal property and infrastructure losses cascade into threats to personal wealth and could affect the economic stability of local governments, businesses, and the broader economy.62 Some coastal property owners are dependent on recouping losses from private or public insurance policies, and there are few private flood insurance policies currently available.63,64 Mortgage holders located within the federally designated Special Flood Hazard Area defined by the Federal Emergency Management Agency are required to purchase flood insurance, which is almost always obtained through the National Flood Insurance Program (NFIP). Losses generated by the NFIP create substantial financial exposure for the Federal Government and U.S. taxpayers.65,66 There are already indications in places like Atlantic City, New Jersey, and Norfolk, Virginia,58,67 that homes subject to recurring flooding may become unsellable. The impacts of Hurricanes Harvey, Irma, and Maria in 2017 will only exacerbate the NFIP losses. (For more information on the 2017 Atlantic hurricane season, see Ch. 2: Climate, Box 2.5.) Additionally, diminished real estate values are likely to result in lower tax revenues and reduced community services (Ch. 28: Adaptation, KM 5).68,69
In addition to private property risks, coastal infrastructure, such as roads, bridges, tunnels, and pipelines, provides important lifelines between coastal and inland communities, meaning that damage to this infrastructure results in cascading costs and national impacts (Ch. 12: Transportation, KM 1 and 2).70 Oil and gas from critical energy infrastructure along the coast is distributed to the entire nation.71,72 Similarly, the entire country depends on coastal seaports for access to goods and services, as they handle 99% of overseas trade (Ch. 12: Transportation, KM 1). Incorporating adaptation into infrastructure upgrades will be expensive. For instance, the estimated cost to elevate and retrofit the major commercial ports of California (such as San Diego, Los Angeles/Long Beach, San Francisco) to adapt to 6 feet of SLR is $9–$12 billion.73 Investing in these interconnected lifelines would support community stability and the Nation’s economy (Ch. 3: Water, KM 2; Ch. 11: Urban, KM 3; Ch. 17: Complex Systems, KM 1 and 3).70