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A Conterminous USA-Scale Map of Relative Tidal Marsh Elevation
James R Holmquist1, Lisamarie Windham-Myers2
1Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037 USA.
Estuaries and Coasts : Journal of the Estuarine Research Federation
|July 29, 2022
Summary
A new national map of relative tidal elevation (Z*MHW) reveals increasing flooding risk from north to south in US tidal wetlands. This metric, normalized to tidal amplitude, highlights vulnerability to sea-level rise and varying LiDAR data quality.
Area of Science:
- Environmental Science
- Coastal Ecology
- Geospatial Analysis
Background:
- Tidal wetlands provide crucial ecosystem services but face uncertain futures due to sea-level rise.
- Existing data limitations hinder national-scale assessments of tidal wetland flooding drivers and vulnerability.
- Diverse elevation gradients and tidal amplitudes across the US complicate broad geographic comparisons.
Purpose of the Study:
- To construct the first national-scale map of relative tidal elevation (Z*MHW) for the conterminous USA.
- To analyze geographic trends in Z*MHW and its variability, and their relationship with tidal amplitude and sea-level rise.
- To assess the impact of data uncertainty, particularly from LiDAR, on Z*MHW calculations.
Main Methods:
- Developed a 30x30m resolution national map of relative tidal elevation (Z*MHW).
- Normalized elevation data to tidal amplitude at mean high water (MHW).
- Analyzed spatial patterns and propagated uncertainty in Z*MHW across different US coastal regions.
Main Results:
- Contrary to hypotheses, median Z*MHW and its variability generally increased from north to south.
- Increased Z*MHW and variability correlate with higher tidal amplitudes and relative sea-level rise.
- Propagated uncertainty in Z*MHW increased southward, with LiDAR errors significantly impacting microtidal areas.
Conclusions:
- The national Z*MHW map provides a critical tool for understanding tidal wetland vulnerability to sea-level rise.
- Latitude-driven factors like tidal amplitude and sea-level rise significantly influence Z*MHW and its uncertainty.
- Future research should focus on validating map products and applying them to carbon dynamics and vulnerability assessments.
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