MODELING APPLICATIONS TO FORECAST SEA-LEVEL RISE AND COASTAL HABITAT MIGRATION UNDER CLIMATE CHANGE

Eustatic sea level has reportedly been rising since the last ice age and over the last century by nearly 2 mm/year. Relative sea-level (RSL) rates vary by coastal reach and are dictated by land subsidence, uplift, and other surficial processes. In some regions, RSL rates are identical or close to eustatic SL, while in other regions RSL can exceed eustatic rates. Long-term tide gage records are among the most reliable measures of local and regional land motion and provide the basis for generating projected sea-level heights under climate change. Complementary tools and models that use on-shore tide gage records and short-term off-shore satellite altimetry observations have been developed by the U.S. Geological Survey to construct future sea-level trends and to predict coastal submergence for different coastal reaches and climate change scenarios.

Coastal wetlands are a critical habitat that is being affected by RSL. The impact of sea-level rise on intertidal wetlands and marsh migration upslope is still poorly understood, but field evidence indicates that tidal freshwater forests exhibit direct loss of structure, density, and species diversity from modest increases in soil salinity initiated by complex interactions of storm tides and droughts. For example, baldcypress (Taxodium distichum) is the most salt tolerant of freshwater tree species and last survivor common to degraded, monospecific stands along the marsh-estuarine ecotone for much of the southeastern U.S. coastline. The distribution and range of baldcypress corresponds with the elevation of ancient sea level (about 120 m above current sea level) dating back to highstand shoreline of the Late Cretaceous epoch nearly 65 million years ago. We will present several examples from different wetland types and various ecological modeling applications to show their utility as decision-support tools for adaptation planning and land management under different climate change scenarios.