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Environmental Modeling



Last updated: December 6, 2012


SLAMM: Sea Level Affecting Marshes Model

SLAMM Model Overview

Tidal marshes are among the most susceptible ecosystems to climate change, especially accelerated sea level rise (SLR).  Changes in tidal marsh area and habitat type in response to sea-level rise may be modeled using the Sea Level Affecting Marshes Model (SLAMM 6) that accounts for the dominant processes involved in wetland conversion and shoreline modifications during long-term sea level rise (Park et al. 1989;www.warrenpinnacle.com/prof/SLAMM).

SLAMM simulates the dominant processes involved in wetland conversions and shoreline modifications during long-term sea level rise. A complex decision tree incorporating geometric and qualitative relationships is used to represent transfers among coastal classes. Each site is divided into cells of equal area; each cell has an elevation, slope, and aspect.

SLAMM Raster Representation

Within the contiguous United States, most required data for the model (NOAA tidal data, Fish & Wildlife Service National Wetland Inventory data, and USGS DEM data) are readily available for download from the Web. If LiDAR elevation data are available they can also be utilized by the model and such high-quality elevation data is highly recommended to reduce model uncertainty.

Successive versions of the model have been used to estimate the impacts of sea level rise on the coasts of the U.S. (Titus et al., 1991; Lee et al.,  1992; Park et al., 1993; Galbraith et al., 2002; National Wildlife Federation et al., 2006; Glick et al. 2007; Craft et al., 2009). 

Relative sea level change is computed for each site for each time step; it is the sum of the historic eustatic trend, the site-specific rate of change of elevation due to subsidence and isostatic adjustment, and the accelerated rise depending on the scenario chosen (Titus et al., 1991; IPCC, 2001).

Within SLAMM, there are five primary processes that affect wetland fate under different scenarios of sea-level rise:

  • Inundation:        The rise of water levels and the salt boundary are tracked by reducing elevations of each cell as sea levels rise, thus keeping mean tide level (MTL) constant at zero.  Spatially variable effects of land subsidence or isostatic rebound are included in these elevation calculations.  The effects on each cell are calculated based on the minimum elevation and slope of that cell. 
  • Erosion:              Erosion is triggered based on a threshold of maximum fetch and the proximity of the marsh to estuarine water or open ocean.  When these conditions are met, horizontal erosion occurs at a rate based on site- specific data.
  • Overwash:          Barrier islands of under 500 meters width are assumed to undergo overwash at a user-specified interval.  Beach migration and transport of sediments are calculated.
  • Saturation:          Coastal swamps and fresh marshes can migrate onto adjacent uplands as a response of the fresh water table to rising sea level close to the coast.
  • Accretion:           Sea level rise is offset by sedimentation and vertical accretion using average or site-specific values for each wetland category.  Accretion rates may be spatially variable within a given model domain.  

Example of Salt Marsh Zonation  

SLAMM Version 6.0 is the latest version of the SLAMM Model, developed in 2009 and closely based on SLAMM 5.  SLAMM 6 is the first open-source version of SLAMM and also provides the following refinements:

  • Accretion Feedback Component: Feedbacks to vertical accretion of wetlands based on elevation, distance to channel, and salinity may be specified. 
  • Salinity Model: Multiple time-variable freshwater flows may be specified. Salinity is estimated and mapped at MLLW, MHHW, and MTL. Habitat switching may be specified as a function of salinity. 
  • Integrated Elevation Analysis: SLAMM will summarize site-specific elevation ranges for wetlands as derived from LiDAR data or other high-resolution data sets.
  • Flexible Elevation Ranges for land categories: If site-specific data indicate that wetlands range beyond the SLAMM defaults a different range may be specified within the interface.  Improved Memory Management: SLAMM no longer requires contiguous memory which improves memory management considerably. 
  • SLAMM 6 allows a user to import a spatial map of uplift and subsidence.
  • Additional and significant graphical user interface upgrades were completed.


All model results are subject to uncertainty due to limitations in input data, incomplete knowledge about factors that control the behavior of the system being modeled, and simplifications of the system (CREM 2008).


  • Craft C, Clough J, Ehman J, Guo H, Joye S, Machmuller M, Park R, and Pennings S.  Effects of Accelerated Sea Level Rise on Delivery of Ecosystem Services Provided by Tidal Marshes: A Simulation of the Georgia (USA) Coast.  Frontiers in Ecology and the Environment. 2009; 7, doi:10.1890/070219
  • Council for Regulatory Environmental Modeling, (CREM)  2008. Draft guidance on the development, evaluation, and application of regulatory environmental models. P Pascual, N Stiber, E Sunderland - Washington DC: Draft, August 2008
  • Galbraith, H., R. Jones, R. A. Park, J. S. Clough, S. Herrod-Julius, B. Harrington, and G. Page. 2002. Global climate change and sea level rise: potential losses of intertidal habitat for shorebirds. Waterbirds 25: 173-183.
  • IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K.Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp.
  • Lee, J. K., R. A. Park, and P. W. Mausel. 1992. Application of Geoprocessing and Simulation Modeling to Estimate Impacts of Sea Level Rise on the Northeast Coast of Florida. Photogrammetric Engineering and Remote Sensing 58: 1579-1586.
  • Lee, J. K., R. A. Park, P. W. Mausel, and R. C. Howe. 1991. GIS-related Modeling of Impacts of Sea Level Rise on Coastal Areas. Pages 356-367. GIS/LIS '91 Conference, Atlanta, Georgia.
  • McKee, K. L. and W. H. Patrick, Jr. 1988. The relationship of smooth cordgrass Spartina alterniflora to tidal datums: A review.  Estuaries. 11:143-15
  • NWF, 2006. An Unfavorable Tide -- Global Warming, Coastal Habitats and Sportfishing in Florida, National Wildlife Federation, Florida Wildlife Federation, June 2006. 56 pages.
  • Park, R. A. 1991. Global Climate Change and Greenhouse Emissions. Pages 171-182. Subcommittee on Health and Environment, U.S. House of Representatives, Washington DC.
  • Park, R. A., T. V. Armentano, and C. L. Cloonan. 1986. Predicting the Effects of Sea Level Rise on Coastal Wetlands. Pages 129-152 in J. G. Titus, ed. Effects of Changes in Stratospheric Ozone and Global Climate, Vol. 4: Sea Level Rise. U.S. Environmental Protection Agency, Washington, D.C.
  • Park, R. A., J. K. Lee, and D. Canning. 1993. Potential Effects of Sea Level Rise on Puget Sound Wetlands. Geocarto International 8: 99-110.
  • Park, R. A., J. K. Lee, P. W. Mausel, and R. C. Howe. 1991. Using Remote Sensing for Modeling the Impacts of Sea Level Rise.World Resource Review 3: 184-205.
  • Park, R. A., M. S. Trehan, P. W. Mausel, and R. C. Howe. 1989a. The Effects of Sea Level Rise on U.S. Coastal Wetlands. Pages 1-1 to 1-55. in J. B. Smith and D. A. Tirpak, eds. The Potential Effects of Global Climate Change on the United States, Appendix B - Sea Level Rise. U.S. Environmental Protection Agency, Washington, D.C.
  • Park, R. A., M. S. Trehan, P. W. Mausel, and R. C. Howe. 1989b. The Effects of Sea Level Rise on U.S. Coastal Wetlands and Lowlands. Pages 48 pp. + 789 pp. in appendices. Holcomb Research Institute, Butler University, Indianapolis, Indiana.
  • Titus, J. G., R. A. Park, S. P. Leatherman, J. R. Weggel, M. S. Greene, P. W. Mausel, M. S. Trehan, S. Brown, C. Grant, and G. W. Yohe. 1991. Greenhouse Effect and Sea Level Rise:  Loss of Land and the Cost of Holding Back the Sea. Coastal Management 19: 171-204.
  • Titus, J.G., and Narayanan, V. K., 1995. The Probability of Sea Level Rise, Washington, D.C., Environmental Protection Agency.
  • Titus, J.G. and C. Richman, 2001: Maps of lands vulnerable to sea level rise: modeled elevations along the U.S. Atlantic and Gulf coasts.Climate Research, 18(3): 205-228.
  • US Climate Change Science Program, 2009, Synthesis and Assessment Product 4.1,Coastal Sensitivity to Sea Level Rise:  A Focus on the Mid-Atlantic Region, January 15, 2009, U.S. Climate Change Science Program And the Subcommittee on Global Change Research, Lead Agency U.S. Environmental Protection Agency.
  • Vermeer, M., and Rahmstorf, S. 2009.  Global sea level linked to global temperature. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0907765106.

For more information, please download the technical documentation available on the main SLAMM page.


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