Progress Toward Restoring the Everglades The Fifth Biennial Review: 2014 (2014) / Chapter Skim
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5 Climate Change and Sea-Level Rise: Implications for Everglades Restoration
5 Climate Change and Sea-Level Rise: Implications for Everglades Restoration
Pages 131-168
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From page 131... ...
. Warmer climates accompanied by changes in precipitation patterns and increases in atmospheric carbon dioxide concentrations will affect wetland ecosystem functioning through changes in hydrologic conditions, biogeochemistry, and primary productivity, and alter linkages with the built environment.
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From page 132... ...
The green, blue, and red lines between 1900 and 2010 represent yearly average global mean sea level reconstructed from tide gages using three different methods, while the light blue line represents satellite altimetry data. The future projections show median estimates and likely ranges for future sea-level rise for a low-emissions scenario (RCP2.6; blue)
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From page 133... ...
is a multidecadal restoration effort, it is important to understand how anticipated changes in climate and sea level could impact restoration outcomes. Climate Projections Accurate projection of climate change and its effects is a major challenge under the best of circumstances, but these challenges are amplified in the complex meteorological environment and landscape of South Florida.
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From page 134... ...
In contrast, dynamical down scaling uses GCM meteorological output as input to a mesoscale climate model to simulate potential future climate regionally or locally. Although investigations have shown that both statistical and dynamically downscaled data are able to reproduce historical temperature and precipitation patterns for Florida, there are biases in these relationships which challenge the accuracy of future down scaled projections.
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From page 135... ...
TABLE 5-1 Summary of Climate Change Projections for South Florida for 2060 Statistically Dynamically Variable GCMs Downscaled Downscaled Average temperature (°C) 1 to 1.5 1 to 2 1.8 to 2.1 Precipitation −10% to +10% −5% to +5% −76 to +50 mm (−3 to +2 inches)
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From page 136... ...
136 Progress Toward Restoring the Everglades FIGURE 5-3 Box and whisker plots showing magnitude and variability of different downscaled GCM-projected changes in (top) temperature and (bottom)
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From page 137... ...
Sea-Level Rise Sea-level rise is already impacting South Florida. Sea level is certain to continue to rise, although the rate of the increase depends on global factors such as future greenhouse gas emissions, thermal expansion of the ocean, and the extent of melting from glaciers and ice sheets (IPCC, 2013)
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From page 138... ...
Thus, it is reasonable that the local USACE projections fully encompass and, at the upper projections, exceed U.S. Army Corps of Engineers EC 1165-2-212 Relative Sea Level Rise Scenarios for Key West, FL 8.00 Relative Rise (meters)
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From page 139... ...
. the most recent global sea-level rise projections of the IPCC (2013; 11-38 inches by 2100; see Figure 5-1)
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From page 140... ...
In addition to the uncertainties in climate projections discussed in the preceding section, South Florida water management operations may also change in response to changing climate. For example, the water level in coastal canals could be maximized to buffer the coastal groundwater system against saltwater intrusion (Obeysekera et al., 2011a)
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From page 141... ...
2010 Baseline with 10 percent increase in rainfall, 1.5oC increase in temperature, and a 1.5-ft increase in sea level with increases in coastal canal levels. These hypothetical climate scenarios are reasonable changes that might be anticipated based on statistically downscaled GCM projections for South Florida for 2060 (Table 5-1)
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From page 142... ...
Implications for Everglades Landscapes The Everglades landscape is especially sensitive to rising sea level because it has low topographic relief of porous limestone bedrock and is in close proximity to the ocean. The topography of the Everglades is shaped by two components: a dynamic surficial layer of wetland soil and the stable floor of the underlying bedrock basin (Gleason and Stone, 1994; Parker and Cooke, 1944; Petuch and Roberts, 2007)
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From page 143... ...
. Lake Okeechobee, while the bedrock underlying the Shark River Slough rises less than 3.3 ft above mean sea level (Parker and Cooke, 1944)
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From page 144... ...
Rates of coastal peat and inorganic sediment accretion or subsidence will directly influence the rate of coastal wetland retreat and other impacts of sea
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From page 145... ...
. Continual monitoring of surface elevations is, therefore, needed over extended time periods to determine the response of wetland deposits to rising sea level.
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From page 146... ...
. The ability of mangroves to keep pace with sea-level rise and persist in situ is also uncer tain because accretion rates are highly variable and dependent not only on sufficient freshwater inflows to prevent oxidation of existing peat but also factors that control pro ductivity of the vegetation and rates of organic matter inputs that drive accretion rates.
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From page 147... ...
. Thus, it remains highly questionable whether accretion rates in coastal wetlands will be sufficient to prevent inundation and retreating shorelines in the future or to what extent accretion could at least mitigate the impacts.
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From page 148... ...
Accretion rates can then be calculated by dividing the length of each section by its total age, although much finer age resolution is often possible for a 210Pb chronology. The alternative method directly measures shorter term changes in surface elevation by means of custom gauges (e.g., the sediment erosion table-marker horizon [SET]
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From page 149... ...
, and therefore, caution should be exercised in extrapolating short-term rates to longer timescales. FIGURE 5-9 Measurement of soil accretion using the marker horizon method in Everglades National Park.
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, and associated biogeochemical processes that ultimately have significant effects on water quality. Reduced precipitation and increased evapotranspiration will decrease the water content of wetland soils.
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From page 151... ...
are likely to generate complex effects that are difficult to fully predict. Changes in precipitation, temperature, sea-level rise, and atmospheric carbon dioxide, in conjunction with anthropogenic alterations to hydrology, will collectively dictate the future environmental templates to which species respond.
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From page 152... ...
, freshwater flows can continue to maintain the diverse array of habitats in the Everglades and abate saltwater intrusion of coastal wetlands, essentially holding the sea at bay (Gaiser et al., 2012, Saha et al., 2012)
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IMPLICATIONS FOR THE CERP AS ORIGINALLY DEVELOPED Rising sea level and changes in evapotranspiration and precipitation could have significant effects on the success of the CERP.
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From page 154... ...
. To consider how future sea-level rise might affect the CERP, the committee considered three projects or areas targeted for CERP restoration: Picayune Strand, Biscayne Bay Coastal Wetlands, and Florida Bay.
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From page 155... ...
Those that are vulnerable to sea-level rise may require the addition of pump stations in place of gravity-driven control structures.
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From page 156... ...
. On the basis of these analyses, planners concluded that project benefits over the 50-year planning horizon were sufficient to recommend the project, noting that the project would "delay future degradation of coastal wetland habitat caused by increased sea level conditions by redirecting freshwater flows into critical habitat" (USACE and SFWMD, 2012b)
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From page 157... ...
Florida Bay is a unique estuarine system with salinity determined by evaporation and precipitation as well as freshwater inputs. Water management changes in the South Florida ecosystem over the past 60 years have reduced freshwater inflows to the bay such that it can be seasonally hypersaline in the middle parts of the bay (Figure 5-12; Kelble et al., 2007; Nuttle et al.,
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From page 158... ...
Increases in sea level of 2 ft (roughly the intermediate USACE local sea-level rise projec tion for 2100) would change the average depth of Florida Bay from 3 to 5 ft, presumably causing a significant change in salinity (e.g., Monismith et al., 2002)
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From page 159... ...
. The combination of increased coupled evapotranspiration, decreased precipitation, and rising sea level over future decades represents the worst-case scenario among those modeled.
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160 Progress Toward Restoring the Everglades FIGURE 5-13 Saltwater intrusion interface in Miami-Dade County, and proximity to water supply well fields.
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From page 161... ...
In the face of possible changes in hydrologic conditions and sea-level rise, increasing water storage to provide more reliable flow to the Everglades as well as to water users could provide useful operational flexibility. For example, maximizing the ability to capture and store water in surface-water reservoirs during wet periods that would otherwise be discharged through the northern estuaries would also provide water for environmental and human uses during dry periods and increase groundwater recharge to mitigate salinity intrusion into South Florida aquifers.
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From page 162... ...
USACE project planning guidance (USACE, 2011e) specifically includes a method for estimating sea-level rise in project design, and the USACE requires analysis of three sea-level rise scenarios for all Civil Works projects (discussed earlier for Biscayne Bay Coastal Wetlands and Picayune Strand)
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From page 163... ...
. The analysis considers the reduction in overall project-derived benefits due to seawater inundation of freshwater wetlands in the project area.
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From page 164... ...
(2014) used a hydrodynamics model to examine the effects of changes in sea level and precipitation on freshwater flows, surface-water salinity, and inundation within Everglades National Park and coastal areas to the east.
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From page 165... ...
Improved salinity modeling tools are needed, such as 3-D circulation models for the major estuaries coupled to regional hydrologic models, as discussed previously in this chapter. Understanding salinity intrusion in coastal wetlands and aquifers used for urban water supply requires a surfacewater flow model coupled with a variable-density groundwater flow model (e.g., Tides and Inflows in the Mangroves of the Everglades [TIME]
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From page 166... ...
Current impacts of rising sea levels are a harbinger of future climate change effects on the functioning and structure of the Everglades ecosystem and the eco system services on which South Florida depends. Sea-level rise in South Florida is already increasing saltwater intrusion into Everglades freshwater habitats and urban water supplies, and future climate changes are likely to be manifested through changes in the timing, volume, and quality of freshwaters; distributions of species; and the extent of wetland habitats.
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From page 167... ...
To decrease uncertainty associated with precipitation projections and clarify future risk, global climate model projections of intra-annual, annual, and interannual variability in precipitation and temperature need to be improved and refined. These improved climate projections should, in turn, be used by CERP planners as input to drive Everglades hydrologic models suitable for making inferences on year-to-year and seasonal variations in freshwater availability.
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From page 168... ...
The committee identified several high-priority research needs related to climate change and Everglades restoration: • Assess the rates of peat/sediment accretion and subsidence in coastal and inland freshwater wetlands in the context of sea-level rise; • Improve modeling tools that can be used to assess the effects of projected sea-level rise on groundwater supplies and coastal ecosystem functioning, and examine the potential for the CERP to mitigate these effects; • Improve, refine, and evaluate downscaled climate model projections in the context of South Florida water resources and Everglades restoration; • Improve the understanding of factors that could help maintain the diverse mosaic of Everglades habitats and increase their resilience amid changes in climate and sea level; and • With improved climate and sea-level projections, reevaluate the goals for Everglades restoration and develop alternate goals as appropriate.
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