Florida, the lowest-lying state in the continental U.S., is uniquely susceptible to the encroaching ocean. The question of how much of Florida is underwater involves both temporary tidal effects and the long-term threat of permanent land loss. Rising waters affect the state’s land from below as well as from the sea. Understanding this dual threat requires examining Florida’s geology, current water dynamics, and future sea level rise projections.
Florida’s Unique Geological Vulnerability
The physical geography of Florida makes it particularly susceptible to water encroachment. The state’s average elevation is quite low, and it lacks the high ground that would typically offer a natural defense against rising seas. This low relief means a small increase in ocean height can translate into a significant movement of water inland.
The peninsula rests upon a porous limestone bedrock, a geological structure known as karst topography. This rock behaves like a sponge, filled with interconnected holes and channels created by millennia of water erosion. Because of this structure, saltwater not only washes over the coast but also pushes up from underneath the land.
The high water table throughout much of the state sits just a few feet below the surface in many coastal areas. Water flows easily through the porous rock, circumventing human-made barriers like seawalls and flood gates. Therefore, any rise in sea level causes a corresponding rise in the groundwater table, increasing the risk of saturation and flooding from below.
Current Effects of Coastal Water Dynamics
The immediate reality of Florida’s water dynamics is seen in cyclical, non-permanent flooding that is becoming more frequent. This phenomenon is often referred to as “sunny-day flooding” or “nuisance flooding,” which occurs even without a major storm event. These events are primarily driven by King Tides, the highest predicted high tides of the year, which are now exacerbated by a slightly elevated sea level.
In coastal cities like Miami Beach and St. Augustine, these King Tides push water up through storm drains and onto streets, sometimes lasting for days. The Southeast Atlantic and Gulf Coast regions of the U.S. have seen the frequency of these high-tide flood days increase by over 400% to 1,100% since 2000. This is a clear, observable sign that the ocean is already operating at a higher baseline.
A more pervasive current consequence is saltwater intrusion into the state’s freshwater supplies. The Biscayne and Floridan Aquifers, which provide drinking water to millions, are being contaminated as the ocean’s saline wedge moves inland. This has already forced municipalities in South Florida, such as Dania Beach and Hallandale Beach, to abandon or relocate coastal wells.
Sea Level Rise Scenarios and Future Inundation Mapping
The long-term answer to “how much of Florida is underwater” is defined by projections of permanent land loss due to sea level rise. Climate models offer a range of scenarios, but there is high confidence in near-term projections, which show an accelerating rate of rise. The U.S. coastline is projected to experience a sea level rise of 10 to 12 inches by 2050, an amount equal to the total rise recorded over the entire 20th century.
For Southeast Florida, this acceleration translates to an anticipated rise of 6 to 10 inches by 2030 and 14 to 26 inches by 2060, based on mid-range projections. Under higher-emissions scenarios, the total sea level rise could reach 31 to 61 inches by the end of the century, with some high-end planning values reaching 81 inches. These specific measurements are used to create inundation maps that forecast which areas will be permanently submerged.
The Florida Keys and the Everglades are among the most vulnerable regions in the world. The Keys, with their low elevation, face the threat of losing at least 38% of their current land area under worst-case projections by 2100. The Everglades National Park, a vast, low-lying wetland, is particularly susceptible to total inundation because of its flat topography.
Inundation mapping for a permanent three-foot rise shows that large portions of coastal Miami-Dade and the Tampa Bay area would be submerged. This level of rise would permanently flood significant sections of the state’s most populated coastal counties. The extent of permanent land loss corresponds directly to the eventual height of the ocean.