SLAMM 4 - Warren Pinnacle



Application of SLAMM 4.1 to Nine

Sites in Florida

For: National Wildlife Federation

Patty Glick

Climate Change Specialist

6 Nickerson Street, Suite 200

Seattle, WA 98109

February 16, 2006

Jonathan S. Clough, Warren Pinnacle Consulting, Inc

PO Box 253, Warren VT, 05674

(802)-496-3476

Application of SLAMM 4.1 to Nine Sites in Florida

Project Background 1

Model Summary 2

Sea Level Rise Scenarios 2

Model Results 4

All of Florida 4

Pensacola: 5

Apalachicola 9

Tampa Bay 11

Charlotte 13

Florida Bay 17

Biscayne Bay 19

Saint Lucie 21

Indian River Lagoon 23

Model Parameterization 25

Project Background

The SLAMM 4.1 model was applied to nine sites within Florida, comprising over 1.7 million hectares (Figure 1). Funding for this model application was provided by the National Wildlife Federation. Extensive data processing that made this application possible was provided by Brad Nunley, NWF’s GIS expert.

Figure 1: Map of Sites Modeled within Florida [pic]

SLAMM Version 4.1 is the latest version of the SLAMM Model, developed in 2005 and based on SLAMM 4.0. SLAMM 4.1 provides additional sea level rise scenarios based on the latest IPCC findings (IPCC 2001) and additional data examination tools to ensure that data quality is acceptable. Model flexibility has been improved with respect to accretion rates, and the model now accepts data from the USGS seamless data distribution tool (seamless.). To accurately model erosion in larger sites, maximum fetch is now calculated on a cell-by-cell basis rather than being input as a site characteristic. For more information on the development of the SLAMM model, please see the model’s technical documentation (Clough and Park, 2005).

Model Summary

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

• Inundation: The rise of water levels and the salt boundary is tracked by reducing elevations of each cell as sea levels rise, thus keeping MTL constant at zero. 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 parameters.

• Overwash: Barrier islands of under 500 meter width are assumed to undergo overwash during each 25 year time-step due to storms encountered. Beach migration and transport of sediments are calculated.

• Saturation: Coastal swamps and fresh marshes can migrate onto adjacent uplands as a response of the water table to rising sea level close to the coast.

For a thorough accounting of each of these processes and the underlying assumptions and equations, please see the model’s technical documentation.

Sea Level Rise Scenarios

The model was run given the minimum, mean, and maximum estimates of each of the SRES scenarios. A brief description of each of these scenarios can be found in the SLAMM 4.1 technical documentation, more extensive descriptions are in the Intergovernmental Panel on Climate Change report (IPCC 2001). For simplicity, this report will focus on the A1 scenario in which the future world includes very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. In particular, the A1B scenario assumes that energy sources will be balanced across all sources.

Figure 2: Summary of SRES Scenarios

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Model Results

All of Florida

Looking at the combined results of all modeled sites can be informative. At present we will focus on the mean results of sea level rise for Scenario A1B. By the year 2100, dry land is predicted to decrease by 14 percent over all sites, due to the processes of inundation and saturation. Hardwood swamp loss is predicted to be 12%. Nearly 50% of salt marsh is predicted to be lost over all sites by the year 2100. Due to the inundation of dry land, transitional salt marsh (brackish marsh) is predicted to increase dramatically. The model also predicts roughly a 40% loss of ocean beaches and that two thirds of estuarine beaches will disappear (primarily to erosion, but also due to overwash, and inundation). As sea levels rise, open ocean and estuarine water is predicted to increase. Mangroves are also expected to thrive under these conditions, gaining by 33%.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for all Sites Modeled in Florida

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If we run the model using the “maximum” estimates for scenario A1B, loss of dry land increases to 22% (from 14%), but salt marsh actually increases by 75% as dry land is converted beyond transitional marsh into pure salt marsh due to continuing inundation. Mangroves do even better under scenarios of higher sea level rise, gaining by over 60% under the maximum scenario.

Pensacola:

Relatively steep slopes of dry land around Pensacola, FL result in a relatively low loss rate for dry land (6-7%), the majority of dry-land loss is predicted due to saturation (increase of height of water table leading to fresh marsh expansion) rather than inundation. Some migration of the barrier islands are predicted with a two thirds loss of ocean beach under the mean scenario. Salt marsh in this region is predicted to be quite vulnerable, however, with a loss of over 70% in both the mean and maximum parameter set.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Pensacola, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Pensacola, FL

Pensacola, FL Current Condition

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Pensacola, FL Year 2100, A1B Mean

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Detail of Elevational Map for Pensacola, FL Barrier Islands

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Apalachicola

Significant loss of hardwood swamp is predicted, particularly along the Apalachicola river where swamp elevations are low relative to sea level. SLAMM predicts that 13-16 percent of these swamps will convert to brackish (transitional) salt marsh. Inundation and saturation is also predicted to convert over a quarter of the dry land on this site, again, particularly along the river basin. Overwash is predicted to have significant effects on the barrier islands to the south of this site.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Apalachicola FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Apalachicola , FL

Apalachicola, FL Current Condition

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Apalachicola, FL Year 2100, A1B Mean

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Tampa Bay

Tidal flats around Tampa bay are predicted to nearly disappear by the year 2100. The barrier islands around Tampa bay are also predicted to be hit hard, with a resulting loss of 10% to 16% of dry lands for the site. Some cypress swamp saturation is also predicted to occur. Mangroves are predicted to roughly double or triple at the site depending on whether the mean or maximum scenario is evaluated.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Tampa Bay, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Tampa Bay, FL

Tampa Bay, FL Current Condition

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Tampa Bay, FL Year 2100, A1B Mean

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Charlotte

Like Tampa Bay, significant overwash is predicted for the barrier islands around Charlotte resulting in much dry land loss. Saturation and inundation also take their toll with dry land predicted to drop a whopping 35-55% depending on whether the mean or maximum scenario is run. Tidal flats are also predicted to be decimated by sea level rise. Mangroves thrive under these scenarios, though, increasing by 75% to 120%. Results in this region are similar to Tampa Bay, though lower elevations of dry land result in more significant predicted impacts here.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Charlotte, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Charlotte, FL

Charlotte, FL Current Condition Charlotte, FL Year 2100, A1B Mean

[pic][pic]

Ten Thousand Islands

What little dry land is at this site is predicted to be lost under these sea level rise scenarios (or at least 80-90% of it). Tidal flats are predicted to migrate further inland while Mangroves, which are already dominant at this site increase from 16% to 26%. Mangrove migration takes its toll on inland fresh marsh which decreases by 44% to 79% depending on the scenario evaluated. Over half of salt marsh also is lost in both scenarios. Some fresh marsh is also predicted to be converted to transitional (brackish) salt marsh, which was not initially present at the site.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Ten Thousand Islands, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Ten Thousand Islands, FL

Ten Thousand Islands, Current Condition

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Ten Thousand Islands, FL Year 2100, A1B Mean

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Florida Bay

In Florida Bay, the most significant prediction is the loss of tidal flats which are currently dominant. Under both scenarios, 99% of tidal flats are predicted to be lost. Mangroves, on the other hand, hang tough with losses of only 3% to 6% due to inundation. At least half of the small amount of dry land at this site is predicted to be lost under the A1B mean and maximum scenarios.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Florida Bay, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Florida Bay, FL

Florida Bay, Current Condition

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Florida Bay, FL Year 2100, A1B Mean

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Biscayne Bay

In Biscayne Bay, the most heavily developed areas in the northwest portion of the study map are not predicted to suffer extensive losses from sea level rise as these developments are built on relatively high land elevations. Further south, however, lesser developed low lying dry land and freshwater wetlands are predicted to suffer significant inundation effects. The barrier islands at the south of the map are also predicted to undergo inundation and subsequent mangrove expansion, especially under the maximum scenario. The resulting prediction is a loss of dry-land that ranges from 13-30% depending on whether the mean or maximum scenario is evaluated.

Given land elevations at this site, a potential exists for expansion of hardwood swamps as the overall water-table rises. However, this potential is likely to be thwarted due to the extent of developed land. The model also predicts that such potential would be short-lived; as the salt level rises, these freshwater swamps are converted into transitional salt marsh under the maximum scenario. Fresh water marshes suffer a 33% to 89% loss under the two scenarios.

As is often the case, transitional salt marsh and mangrove stands have the potential to increase significantly under these two scenarios of sea level rise as dry lands and fresh marshes undergo inundation. Beach erosion is predicted to claim roughly one third of existing beaches on these sites.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Biscayne Bay, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Biscayne Bay, FL

Biscayne Bay, Current Condition Biscayne Bay, FL Year 2100, A1B Mean

Saint Lucie

The two dominant processes predicted to affect Saint Lucie are overwash of the barrier islands and saturation of dry land. Inland elevations of dry land are low, especially in relation to the inland fresh marsh that occurs close to the bay. This results in significant predictions of saturation and a loss of 10 to 12% of dry land (which is comprises more than 50% of this site). Because this part of Saint Lucie is heavily developed, this prediction should probably be considered the “potential” for saturation as this process is likely to be offset by landowners bringing in fill when required. Beach erosion and overwash is predicted to result in the loss of roughly half of the ocean beach at this site.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Saint Lucie, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Saint Lucie, FL

Saint Lucie, FL Current Condition Saint Lucie, FL Year 2100, A1B Mean

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Indian River Lagoon

As was the case in Saint Lucie, saturation is again an important process at this east coast site resulting in a loss of 15% to 25% of dry land (depending on scenario). Again, as this is a heavily developed site this may be more a prediction of costs to be imposed on landowners rather than an actual loss of dry land. Under the maximum scenario, some of the fresh marsh at the site is converted into transitional salt marsh by the year 2100. Overwash is not predicted to be important at this site, but beach erosion does claim roughly 50% of ocean beach under both scenarios.

SLAMM Predictions of Marsh Fate under Scenario A1B, Mean (Max) for Indian River Lagoon, FL

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SLAMM Predictions of Marsh Fate under Scenario A1B, Mean for Indian River Lagoon, FL

Indian River Lagoon, FL Current Condition Indian River Lagoon, FL Year 2100, A1B Mean

[pic] [pic]

Model Parameterization

• Digital Elevation Maps were downloaded using the USGS seamless data distribution tool ().

• NWI maps were downloaded as polygons and converted to rasters with the appropriate SLAMM category ().

• NOAA data were gathered from 35 sites (Figure 1) to parameterize the model for tidal range, inland tidal range, and “NGVD88 to Mean Tide Level” corrections. See the table below for a summary of NOAA data used to derive parameters.

NOAA Stations, Tide Range, and MTL Corrections

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• Historic sea level rise trend data were downloaded from NOAA and spatially interpolated as necessary. Variation in historic trends were relatively minor (figure below)

Historic Sea Level Rise Trends Measured at NOAA Stations

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• Erosion rates were set to SLAMM defaults. Default erosion rates are 2.0 horizontal meters per year for marshes, 1.0 meter per year for swamps, and 0.5 meters per year for tidal flats. These rates are based on a combination of professional judgment and a brief literature survey. (Note also that these erosion rates presume that a threshold for erosion has been exceeded prior to the incidence of horizontal erosion. See the technical documentation for more information.)

• Accretion rates were set to 2.25 mm/year for salt marshes, 3.75 mm/year for brackish marsh, and 4.0 mm/year for tidal flats. These data were based on measurements from the Altamaha River in Georgia (Personal Communication, Dr. Christopher Craft.) However a literature review of accretion rates, including several measurements from Florida sites, indicate that the above rates are comfortably in-line with measurements taken throughout Florida (D. R. Cahoon, J. W. Day, Jr., and D. J. Reed, 1999. The influence of surface and shallow subsurface soil processes on wetland elevation: A synthesis. Current Topics in Wetland Biogeochemistry, 3, 72-88. ) (D. R. Cahoon, D. J. Reed, J. W. Day, Jr., 1995. Estimating shallow subsidence in microtidal salt marshes of the southeastern United States: Kaye and Barghoorn revisited. Marine Geology, 128, 1-9.)

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