The Southeast’s coastal plain and inland low-lying regions support a rapidly growing population, a tourism economy, critical industries, and important cultural resources that are highly vulnerable to climate change impacts (very likely, very high confidence). The combined effects of changing extreme rainfall events and sea level rise are already increasing flood frequencies, which impacts property values and infrastructure viability, particularly in coastal cities. Without significant adaptation measures, these regions are projected to experience daily high tide flooding by the end of the century (likely, high confidence).

This finding is from chapter 19 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.7bdd9d20-6e83-40ab-8d50-68272c2b3dc9 Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.

Description of evidence base:

Multiple lines of research have shown that global sea levels have increased in the past and are projected to continue to accelerate in the future due to increased global temperature and that higher local sea level rise rates in the Mid-Atlantic and Gulf Coasts have occurred.3bae2310-7572-47e2-99a4-9e4276764934^,c66bf5a9-a6d7-4043-ad99-db0ae6ae562c^,480ff362-8434-4861-a8bb-2dc6615bdcdc^,6b46b616-994d-4fcf-b8d7-1a284bc1bf72^,168f6b1a-bf79-4887-9c82-1a27dcd1c98b^,70b9fb1f-c611-4bb7-ad28-ea752489a5de^,d2dc9855-41bc-4e94-bb79-f0ba2ff2684b^,a0130167-b319-493d-bedc-7cab8f8fe9d9^,d67e2bfd-20fe-4bd8-a491-c3320b7f0044^,d8089822-678e-4834-a1ec-0dca1da35314

Annual occurrences of high tide flooding have increased, causing several Southeast coastal cities to experience all-time records of occurrences that are posing daily risks.df029572-7e7a-4f65-91c2-da86756620c4^,c66bf5a9-a6d7-4043-ad99-db0ae6ae562c^,048006a1-a72d-44a1-bdab-fff317c842f7^,bbf3043e-9999-4f0e-8d0c-6012450d9d84^,d67e2bfd-20fe-4bd8-a491-c3320b7f0044^,91aeffdb-e82f-4645-abe9-f6ea6909e979^,558f520b-2054-428d-9c91-ed31241c30b2^,03e51664-273d-40e5-8af0-ab885436ac8e

There is scientific consensus that sea level rise will continue to cause increases in high tide flooding in the Southeast as well as impact the frequency and duration of extreme water level events, causing an increase in the vulnerability of coastal populations and property.df029572-7e7a-4f65-91c2-da86756620c4^,bbf3043e-9999-4f0e-8d0c-6012450d9d84^,91aeffdb-e82f-4645-abe9-f6ea6909e979^,558f520b-2054-428d-9c91-ed31241c30b2^,03e51664-273d-40e5-8af0-ab885436ac8e

In the future, coastal flooding is projected to become more serious, disruptive, and costly as the frequency, depth, and inland extent grow with time.df029572-7e7a-4f65-91c2-da86756620c4^,2db2b107-2e02-4f3a-b1e7-98301e28395d^,0b30f1ab-e4c4-4837-aa8b-0e19faccdb94^,9f559c9b-c78e-4593-bcbe-f07661d29e16^,e1f4f1b2-6b77-465a-bddb-ed992079deea^,558f520b-2054-428d-9c91-ed31241c30b2^,03e51664-273d-40e5-8af0-ab885436ac8e

Many analyses have determined that extreme rainfall events have increased in the Southeast, and under higher scenarios, the frequency and intensity of these events are projected to increase.e8089a19-413e-4bc5-8c4a-7610399e268c^,8a79ffea-f7c4-4296-a337-33a2e6a5087c^,6239c23d-c1e7-4190-a384-f8283df288ef

Rainfall records have shown that since NCA3, many intense rainfall events (approaching 500-year events) have occurred in the Southeast, with some causing billions of dollars in damage and many deaths.03e51664-273d-40e5-8af0-ab885436ac8e^,0685a072-6516-4a47-80ad-cbbd75fd4dcc^,04aa6da1-18ac-435a-b31d-f4f65da727df

The flood events in Baton Rouge, Louisiana, in 2016 and in South Carolina in 2015 provide real examples of how vulnerable inland and coastal communities are to extreme rainfall events.6acb342f-f144-4fad-ae46-a6ff80f812cf^,70be67ff-723c-4ae4-9df3-16d178c36a48^,60165103-bf76-4bdc-a1f7-f43389eb76f5

The socioeconomic impacts of climate change on the Southeast is a developing research field.e1f4f1b2-6b77-465a-bddb-ed992079deea^,2ddba35f-6036-4428-b4c7-800dd57b3313

New information and remaining uncertainties:

The amount of confidence associated with the historical rate of global sea level rise is impacted by the sparsity of tide gauge records and historical proxies as well as different statistical approaches for estimating sea level change. The amount of unpredictability in future projected rates of sea level rise is likely caused by a range of future climate scenarios projections and rate of ice sheet mass changes. Flooding events are highly variable in both space and time. Detection and attribution of flood events are difficult due to multiple variables that cause flooding.

Assessment of confidence based on evidence:

There is high confidence that flood risks will very likely increase in coastal and low-lying regions of the Southeast due to rising sea level and an increase in extreme rainfall events. There is high confidence that Southeast coastal cities are already experiencing record numbers of high tide flooding events, and without significant adaptation measures, it is likely they will be impacted by daily high tide flooding.

Provenance

This finding was derived from scenario rcp_4_5
This finding was derived from scenario rcp_8_5