Modeling sea-level rise and wave-driven inundation on Laysan Island:

a geospatial approach

Paul Berkowitz, HCSU, UHH

pberkowitz@usgs.gov

May 20, 2014

Laysan Island, Papahānaumokuākea Marine National Monument (PMNM)

• Carbonate island

• Max. elevation ~ 10 m

• Central hyper-saline lake

• Highest dunes in north & west; lowest in east

• No well-defined reef crest

WorldView-2 image (Digital Globe 2010)

Research Objective: Estimate habitat loss on Laysan Island over the next century due to SLR and wave-driven inundation.

Passive (“bathtub”) inundation model

vs.

Wave-driven inundation model.

Geospatial processing steps:

1. Generate seamless topo/bathy grids used by wave-models (Delft3D)

2. Assign wave-driven water levels to coastal points

3. Project water-levels orthogonally up beach slope

4. Delineate inundation extent

5. Account for topography

6. Overlay inundation extent & seabird habitat

Step 1. Generate topo/bathy grids for Delft3D model

PIBHMC depth grid

Navigational Charts 1-m DEM

Digitized Coastline

Input Data Output GridsKriging

100-m resolution

20-m resolution

Step 2. Assign wave-driven water levels to coastal stations

Step 3. Project water-levels orthogonally up beach slope.

Step 4. Delineate inundation extent.

Step 5. Account for topography.

Results:1. Passive models

underestimate inundation extent during periods of high-wave energy.

2. Starting at ~ 1.5 m SLR, wave run-up (during periods of high-wave energy) will breach dunes and start to fill the interior basins.

Step 6. Overlay inundation extent with habitat to assess vulnerability (9 spp.; 5 SLR scenarios; 2 gw assumptions)

Masked & Brown Booby

Laysan TealGreat Frigatebird & Red-footed Booby

Sooty TernLaysan Albatross

Conclusions for Laysan:

1. Passive & wave-driven models predict very different levels of inundation.

2. Most impacts occur at SLR > 1.5 m.

3. Vulnerability varies by species distribution, temporal factors, & species life history.

Overall Conclusions:

Since passive models may significantly understate impacts, more complicated models should be considered.

AcknowledgementsContributors: Michelle Reynolds, Principal Investigator, USGS Pacific Island Ecosystem Research Center (PIERC); Curt Storlazzi, USGS Pacific Coastal and Marine Science Center; Karen Courtot and Crystal Krause, USGS PIERC; Jeff Hatfield, USGS Patuxent Wildlife Research Center; Jamie Carter, NOAA; Matt Stelmach and Tawn Speetjens, USFWS.

Contributing organizations: Papahānaumokuākea Marine National Monument; USGS-Deltares co-operative.

Funding sources: USGS National Climate Change and Wildlife Center, USGS PIERC, USFWS Pacific Islands Refuges Inventory and Monitoring

Report on-line: http://pubs.usgs.gov/of/2012/1182/

pberkowitz@usgs.gov