Sea-Level Rise and High Tide Flooding at De Soto National Memorial, Florida

The view north from De Soto Point, December 2022. Photo: National Park Service.

National parks and preserves in the Park Service's South Atlantic-Gulf Region hold valuable coastal habitats — tidal wetlands, mangrove forests — and irreplaceable historic buildings and archeological sites on low ground. All are vulnerable to faster sea-level rise and more high tide flooding.

In a project funded by the NPS Natural Resources Preservation Program in 2021–23, the U.S. Geological Survey, working with the National Park Service, estimated the probability of inundation at De Soto National Memorial and several other parks under a range of sea-level scenarios and today's high tide flood thresholds. The maps can help gauge habitat change and how the park's infrastructure and cultural resources may be exposed to flooding.

The memorial

De Soto National Memorial lies at the mouth of the Manatee River, at the southern end of Tampa Bay, and covers just 0.12 square kilometer of land (not counting water and aquatic-bed wetlands). Most of it is coastal wetland dominated by black mangrove. Habitats like these survive rising seas only if they can build up in place or move to higher ground, and rising water also puts historic, cultural and recreational sites at risk of damage or loss.

De Soto National Memorial, at the mouth of the Manatee River on Tampa Bay. Map: U.S. Geological Survey; aerial imagery from the U.S. Department of Agriculture National Agriculture Imagery Program.

Two kinds of rising water

Relative sea-level rise. Climate change is raising the seas worldwide, but local rates differ with ocean circulation and density, the land rising or sinking, and where and how much ice sheets and glaciers are losing. A multiagency report set out five global scenarios — low, intermediate-low, intermediate, intermediate-high and high — depending on greenhouse gas emissions and ice loss, and the study used the regional and local projections for each. Each scenario has a median projection and a likely range, the 17th to 83rd percentile.

The five sea-level rise scenarios for the memorial to 2100: each line is the median projection, the shading its likely range. Chart: U.S. Geological Survey.

High tide flooding happens when spring tides — the highest tides, at full or new moon, when Earth, Moon and Sun line up — high winds or storms push water to extreme levels. NOAA sets local thresholds: minor floods disrupt trails and other infrastructure, moderate floods cause more disruption and possible damage, and major floods bring destruction and evacuations.

A trail on the memorial's north shore flooded by high tide flooding in July 2017. Photo: National Park Service.

Along the eastern Gulf of Mexico coast, minor high tide floods now happen only a few days a year, and moderate and major ones less than once a year. Rising seas will change that fast: by 2100, under the intermediate-low scenario, minor flooding is projected to happen more often than every other day — today's flood level could become an ordinary high tide. Many small floods add up to real damage in low-lying areas; tidal flooding is a present-day effect of rising seas and a sign of what is to come.

What the maps show

Projected sea-level rise at the memorial, measured from 1992 (median, with the likely range):

Share of the memorial's non-water area likely to be inundated (probability above 0.66):

Where the memorial is likely to be inundated under the intermediate-low and intermediate-high scenarios in 2050 and 2100. Maps: U.S. Geological Survey.

High tide flood thresholds at the memorial, above mean higher high water: 53 cm (±19) minor, 82 cm (±25) moderate and 120 cm (±39) major. Under all three, most of the memorial's land is likely to flood — from about 63% at the minor threshold to about 80% at the major.

Flooding probability at the minor, moderate and major high tide flooding thresholds. Maps: U.S. Geological Survey.

Using the maps

The maps can help managers assess present and future effects of rising water on habitats, historic and cultural resources, and infrastructure, and support decisions under the resist–accept–direct (RAD) framework. The same approach can show future habitat change, such as tidal saline wetlands migrating inland. The data and methods are in a USGS data release (Thurman and others, 2024b).

Sources

Based on "Projected sea-level rise and high tide flooding at De Soto National Memorial, Florida," U.S. Geological Survey Fact Sheet 2024–3016, U.S. Geological Survey, produced with the National Park Service; a work of the United States government in the public domain. The maps, chart and photographs are reproduced from the fact sheet.