The impact of accelerated sea level rise on coastal wetlands and its implications on storm surge - The story of lower Pascagoula River Basin in Jackson County, MS Wei Wu 1, Maria Kalcic 2, Jason Fleming 3 March 6, The University of Southern Mississippi 2.Computer Science Corp 3.Seahorse Coastal Consulting

GHGs are changing, but growing at a unprecedented accelerated rate Atmospheric concentrations of CO 2, CH 4 and N 2 O over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores and atmospheric samples (red lines). The corresponding radiative forcing relative to 1750 are shown on the right hand axes of the large panels. From IPCC Climate Change 2007: Synthesis report

Surface temperature, seal level and snow cover are changing, but at a unprecedented accelerated rate Observed changes in a)Global average surface temperature; b)Global average sea level from tide gauge (blue) and satellite (red); c)Northern hemisphere snow cover for March-April. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals. From IPCC Climate Change 2007: Synthesis report

Consequences of climate change Alter ecosystem services and affect the ability of biological systems to support human needs (Vitousek et al. 1997) e.g. degradation in water quality, productivity and extractable resources; Interact with other environmental stressors: elevated acidic atmospheric deposition, accelerated sea level rise, hurricanes etc.

Coastal wetland Coastal wetlands are ecologically, economically and socially important to humans as they provide the benefits of storm protection, flood control, habitat for commercially important fisheries and wildlife, improved water quality through sediment, nutrient and pollutant removal, recreation, and aesthetic value. In particular, coastal wetlands can reduce storm surge potential by acting as a physical barrier and creating frictional resistance for the surge and waves. They may also reduce surge potential and flooding risks by reducing surface winds due to higher sub-aerial surface roughness and by slowing surge propagation due to bottom friction in shallow flow at the inundation front.

Objectives Simulate the impact of different sea level rise scenarios on coastal wetland; How the area and location changes of coastal wetland affect storm surge predictions

Simulate the impact of SLR on coastal wetland

Method Sea Level Affecting Marshes Model (SLAMM beta) Simulates the dominant processes involved in wetland conversions and shoreline modifications during long-term sea-level rise : Inundation, Erosion, Overwash, Saturation, Accretion, Salinity SLAMM integrates elevation–submergence and wave action– erosion. SLAMM also incorporates a salinity algorithm, based on freshwater discharge and cross-sectional area of the estuary, to model saltwater intrusion in river-dominated estuaries of our study domain. Model inputs included the USGS LiDAR-derived elevation data (vertical accuracy: 12 cm) NOAA tidal data Accretion rates National Wetlands Inventory (NWI) data

Study area – lower Pascagoula River Estuarine 9 th American most endangered rivers Latitude 30º28’N Longitude 88º35’W

Accretion rates Type of wetlandLocationSampling datesSediment Accumulation (cm /y) Freshwater tidal marsh N 30° 28’ 39.20’’ W 88° 35’ 56.50’’ 11/7/ ± 0.20 Brackish marshN 30° 26’ 5.46’’ W 88° 35’ 19.14’’ 4/25/ ± 0.30 Salt marshN 30° 21’45.85’’ W 88° 36’ 35.28’’ 10/7/ ± 0.19 From fallout radionuclides ( 7 Be, 137 Cs, and 210 Pb)

Sea level rise scenario Sea level rise rate is predicted to be 0.10 inch/year to 0.83 inch/year, on Mississippi Gulf Coast, which will be translated to 0.26 m to 2.19 m increase in sea level from 1996 to 2100.

High sea level rise scenario

Low sea level rise scenario

Landscape metrics under high SLR 2100 under low SLR Edge density Perimeter/Area Contiguity index Aggregation index Patch richness density Shannon’s diversity index

High low From 1996 to 2100

Low vs. High sea level rise scenario in 2100

Simulate the impact of changes in coastal wetland on storm surge

Method Advanced CIRCulation (ADCIRC model). Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model: domain is limited and the spatial resolution is very coarse (0.5-7 Km) (International Hurricane Research Center, online). It is difficult to simulate convoluted shorelines and incorporate features that block or accelerate storm surge flooding. In addition, tide and wave set ups are not included, and the overland flooding model is not adequate, thus SLOSH tends to produce large uncertainty and provides only a very rough estimate in the predicted flooded area only. ADCIRC’s domain is flexible, its spatial resolution can reach finer than 50×50 m, it can simulate convoluted shorelines and include features like highways and canals, and it contains tide setup, so it performs better (albeit more slowly) than SLOSH, especially at the shoreline.

Mesh and bathymetry

Storm surge 1996

Water elevation in 1996

Water elevation in 2100 under high SLR scenario

Water elevation in 2100 under low SLR scenario

1996

2100 under high SLR scenario

2100 under low SLR scenario

Conclusion SLR is likely to affect area and distribution of coastal wetlands and therefore alter landscape patterns. Wetland change due to SLR is likely to change storm surge height (e.g % increase under different scenarios of SLR) and affect the pattern of coastal floods (increase the flooded area).

Acknowledgements Mississippi-Alabama Sea Grant Consortium Program Development Mississippi-Alabama Sea Grant Consortium Coastal Storm Program

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