Charleston, South Carolina, is a low-lying coastal city whose geography makes it acutely vulnerable to rising sea levels. The peninsula holds irreplaceable historic architecture and cultural heritage. Surrounded by water on three sides, large sections of downtown sit only slightly above the current high tide mark. Understanding the present reality of its relationship with water and the scientific timelines for future inundation is necessary for addressing the city’s long-term future.
The Current Reality of Water in Charleston
The threat of rising water in Charleston is a daily fact of life known as “nuisance flooding.” This phenomenon, also called “sunny day flooding,” occurs when unusually high tides alone push water into the streets, even without significant rainfall or storms. Flooding events that were once rare are now routine, confirming that the baseline of the problem has already shifted.
The frequency of tidal flooding has increased dramatically over the last few decades. In the 1990s, Charleston typically experienced between 10 and 25 tidal flood events per year. This number has surged significantly, recording 89 events in 2019 and 75 events in 2023. This acceleration means the city now experiences tidal flooding on average every five days, even on clear days.
These high-tide events flood major streets in the historic district, snarling traffic and disrupting commerce. The chronic nature of this flooding directly indicates the overall increase in relative sea level over the last century. This reality sets the stage for the more severe inundation predicted for the coming decades.
Scientific Projections for Coastal Inundation Timelines
Scientific forecasts indicate that the rate of relative sea-level rise in Charleston is accelerating, providing a timeline for when permanent inundation becomes a daily certainty. Relative sea level, which combines the rising ocean with local land movement, has risen by about ten inches since 1950. Since 2010, the rate of this rise has accelerated to approximately one inch every two years.
By 2050, authoritative bodies like the National Oceanic and Atmospheric Administration (NOAA) project a significant additional rise. Under intermediate scenarios, Charleston is expected to experience an additional 10 to 14 inches of sea-level rise relative to current levels. The NOAA Intermediate Scenario, often used for planning, projects an approximate 11-inch increase between 2020 and 2050.
The clearest benchmark for future vulnerability is the frequency of nuisance flooding. NOAA projections suggest that by 2050, Charleston could experience between 70 and 90 high-tide flood days annually under moderate scenarios. Some forecasts predict this frequency could increase to 180 days per year by 2045, meaning parts of the city could face tidal flooding nearly half the year. This shift transforms the current disruptive nuisance into a chronic operational challenge that fundamentally changes how the city functions.
Local Geographic and Geological Factors
Charleston’s exposure to rising waters is compounded by unique geographic and geological factors that cause its relative sea-level rise to be higher than the global average. A primary factor is land subsidence, the sinking of the land mass itself. The Charleston area is sinking at an estimated rate of around four millimeters (0.16 inches) per year.
This subsidence is driven partly by natural geological processes, including the slow rebound of land in the North following the last Ice Age, known as glacial isostatic adjustment. Human activity exacerbates this sinking, particularly the historic practice of filling in low-lying marshlands and creeks for development. Much of the historic peninsula, including frequently flooded areas, was built on this unstable fill.
The city’s surrounding geography further amplifies the effects of a rising ocean. The large tidal range in the harbor and the funneling effect of surrounding estuaries and rivers push higher volumes of water into the area. This combination of a sinking landmass and the increasing volume of the Atlantic Ocean means that small increases in global sea level translate to disproportionately higher relative sea-level increases locally.
Consequences for Infrastructure and Daily Life
The cumulative effect of a rising ocean and sinking land creates tangible threats to Charleston’s built environment and public services. The city’s historic architecture faces direct physical damage from chronic inundation. Many antebellum homes and historic buildings have foundations built just above historic high-tide levels.
As minor flooding becomes a daily or weekly event, the foundations and basements of these structures are subjected to constant dampness and salt intrusion. This leads to structural damage like rotting timbers and weakened masonry. The functional failure of infrastructure is an immediate consequence. Major transportation arteries, such as the Crosstown Expressway and Lockwood Drive, are already prone to flooding and will become increasingly unreliable.
Charleston’s aging drainage and stormwater systems are particularly vulnerable. These systems rely on gravity to drain water into the surrounding harbor and rivers. When high tides are consistently elevated, the water has nowhere to go, causing stormwater and even sewage to back-flow into the streets and buildings. This systemic failure of public works, coupled with the economic impact of lost business days and declining property values, threatens the long-term viability of the city’s historic downtown.