LTC 538-2021 Sea Level Rise Report - Resolution 2018-30418MIAMI BEACH
OFFICE OF THE CITY MANAGER
NO. LTC# 538-2021 LETTER TO COMMISSION
TO: Honorable Mayor Dan Gelber and Members of the City Commission
FROM, Alina T. Hudak, City Manager ~ ~.(\,('
DATE: December 23, 2021
SUBJECT: Sea Level Rise Report - Resolution 2018-30418
On July 25, 2018, the Mayor and City Commission passed Resolution 2018-30418 (Attachment
A) directing the administration to collect and track, on an annual basis, sea level rise data from
the Virginia Key tide gauge and the Southeast Florida Regional Climate Change Compact
(Compact) (or from an alternative preferred data source, if one becomes available). This includes
reporting such data to the City Commission with the goal to facilitate an incremental adaptation
strategy. In accordance with the resolution, the requested historical data from the Virginia Key
tide gauge is provided below. In addition, in July 2020, the Mayor and City Commission adopted
the 2019 update of the Unified Sea Level Rise Projection for Southeast Florida (Attachment B) to
be used for planning purposes. These projections are used for land development regulations,
seawall elevations, and the Road Elevation Strategy, developed by Jacobs Engineering and
adopted by the City Commission.
Southeast Florida Regional Climate Change Compact Unified Sea Level Rise Projection
In 201 O, the Southeast Florida Regional Climate Change Compact (Compact) was formed to
coordinate mitigation and adaptation efforts between Monroe, Miami-Dade, Broward, and Palm
Beach Counties. In 2011, the Compact released the first regionally unified sea level rise
projection. The Compact created the ad hoc Sea Level Rise Work Group composed of scientific
experts within the academic community, as well as staff from local, regional, and federal
government to update the regional projection at regular intervals. Following the first report, the
projection and accompanying guidance report was updated in 2015, and most recently in 2019.
The 2019 update was adopted by the Mayor and City Commission on July 24, 2020.
The Compact's ad hoc Sea Level Rise Work Group updated the most recent Unified Sea Level
Rise Projection for Southeast Florida based on the latest scientific understanding of climate
change and sea level rise for the region, including the Intergovernmental Panel on Climate
Change {IPCC) Fifth Assessment Report (IPCC, 2014), the National Oceanic and Atmospheric
Administration (NOAA), and the U.S. Army Corps of Engineers (USACE) models.
The Unified Sea Level Rise Projection for Southeast Florida accounts for regional effects, such
as gravitation effects of ice melt, changes in ocean dynamics, vertical land movement, and
thermal expansion from warming of the Florida Current that produces regional differences in
Southeast Florida's rate of sea level rise compared to global projections. Climate science is
rapidly advancing, generating new, peer-reviewed literature and modeling.
The Compact updates the projection and guiding document at least every five years to provide
current guidance for regionally consistent sea level rise planning and decision-making. It is
recommended that the City continue to utilize the most recent Unified Sea Level Rise Projection
for Southeast Florida for planning and infrastructure siting and design purposes when
considering both short- and long-term planning horizons.
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Unified Sea Level Rise Projection
(Southeast Florida Regional Climate Change Compact, 2019)
Year
Observed
5-Year Average
Mean Sea Level
IPCC NOAA
d. I Intermediate NOAA High
Median ih (ich«;) (it ch«s) / '&' (incnes
incnes) (inches) -··-
2040 10 j
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40
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REGIONAL COMPACT
54
92 136
92
Intermediate High
NOAA
1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110 2120
Year
Exhibit 2: Southeast Florida Regional Climate Compact Unified Sea Level Rise Projection (2019)
From a global perspective, in 2021, the IPCC released its Sixth Assessment Report
(https://www.ipcc.ch/report/ar6/wg1/downloads/report/lPCC AR6 WGI Full Report.pdf) which
utilized more integrated models and placed a greater focus on regional data. This report found
that "it is unequivocal that human influence has warmed the atmosphere, ocean and land" and
that "human-induced climate change is already affecting many weather and climate extremes in
every region across the globe". It also states that "global warming of 1.5ºC and 2ºC will be
exceeded during the 21° century unless deep reductions in carbon dioxide and other
greenhouse gas emissions occur in the coming decades." IPCC reports are used by the
Compact in the development of localized projections, such as the ones used by the City of
Miami Beach.
Historical Data from NOAA Virginia Key Station
Additionally, the Resolution requested Virginia Key tidal data. The Virginia Key tide station has
been collecting local sea level trends since 1931. The National Oceanic and Atmospheric
Administration's (NOAA) Center for Operational Oceanographic Products and Services (CO-
OPS) maintains the National Water Level Observation Network. This network includes more than
200 permanent water level stations throughout the United States that allow NOAA to provide
official tidal predictions for the nation. Exhibit 1 illustrates the monthly mean sea level at the
Virginia Key Station without the regular seasonal fluctuations due to coastal ocean temperatures,
salinities, winds, atmospheric pressures, and ocean currents. The relative sea level was
2.97mm/year with a 95% confidence interval of +/- 0.21 mm/ year based on monthly mean sea
level data from 1931 to 2020 which is equivalent to a change of 0.97 feet in 100 years
https://tidesandcurrents.noaa.gov/.
Exhibit 1: Relative Sea Level Rise Trend - Virginia Key, Florida
8723214 Virginia Key, Florida 2.97 +/- 0.21 mm/yr
0.60
0.45
0.30
0.15
Ill b 0.00 ..... @» :E
-0.15
-0.30
-0.45
-0.60
1920
- Linear Relative Sea Level Trend /~
Upper 95% Confidence Interval -~• _
Lower 95% Confidence Interval
Monthly mean sea level with the
o geraqeseasonal cycle retoed - - - - - - - - - -
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Conclusion
The Southeast Florida Regional Climate Change Compact updates the sea level rise projection
at minimum every five years to reflect the ongoing advances in scientific knowledge related to
global climate change. On July 24, 2020, the Mayor and City Commission adopted the 2019
update of the Unified Sea Level Rise Projection for Southeast Florida and Miami Beach continues
to utilize the regionally consistent unified sea level rise projection for planning purposes. The
Administration recommends that future sea level rise updates be provided when the Unified Sea
Level Rise Projection for Southeast Florida is updated.
ATP"9AW/YPAs
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A. Resolution 2018-30418
B. 2019 Unified Sea Level Rise Projection for Southeast Florida
RESOLUTION 2018-30418
A RESOLUTION OF THE MAYOR AND CITY COMMISSION OF THE CITY
OF MIAMI BEACH, FLORIDA, DIRECTING THE CITY ADMINISTRATION
TO COLLECT AND TRACK, ON AN ANNUAL BASIS, SEA LEVEL RISE
DATA FROM THE VIRGINIA KEY TIDAL GUAGE AND FROM THE
SOUTHEAST FLORIDA REGIONAL CLIMATE CHANGE COMPACT (OR
FROM AN ALTERNATIVE PREFERRED DATA SOURCE, IF ONE
BECOMES AVAILABLE), AND TO ANNUALLY REPORT SUCH DATA TO
THE CITY COMMISSION IN ORDER TO FACILITATE AN INCREMENTAL
ADAPTATION STRATEGY IN THE CITY.
WHEREAS, sea level rise is a matter of global concern with significant variations in
impact on both regional and local levels; and
WHEREAS, in order to accurately analyze the impacts of sea level rise, data gathered
over a long term horizon should be used to track trends and realities, and short-term anomalies
in environmental conditions and weather should be viewed in their proper perspective; and
WHEREAS, to facilitate the accurate tracking of sea level rise in the City, and the
development of best strategies for the City's incremental adaptation thereto, the City
Administration should collect data from the Virginia Key tidal gauge and obtain projections from
the Southeast Florida Regional Climate Change Compact (or from an alternative preferred data
source, if one becomes available) on an annual basis and annually report such data and
projections to the City Commission; and
WHEREAS, the data collected and reported to the City Commission by the City
Administration should be in both the U.S. Customary System of measurement and the metric
system, the projection data should highlight the cumulative anticipated sea level rise from the
current year level, and the City Administration should include any other related, relevant data
that may inform policy-making.
NOW, THEREFORE, BE IT DULY RESOLVED BY THE MAYOR AND CITY
COMMISSION OF THE CITY OF MIAMI BEACH, FLORIDA, that the Mayor and City
Commission hereby direct the City Administration to collect and track, on an annual basis, sea
level rise data from the Virginia Key tidal gauge and from the Southeast Florida Regional
Climate Change Compact (or from an alternative preferred data source, if one becomes
available), and to annually report such data to the City Commission in order to facilitate an
incremental adaptation strategy in the City.
PASSED AND ADOPTED this 25th day of July, 2018.
ATTEST:
11/ elber, Mayor
/ / fhy AnoveD As7o Rari e oanaa, cy cI° FonM a LANGUAae
& FOR EXECUTION
a± 0, ft r" +, Dae
(Sponsored by Vice-Mayor Mark Samuel
Resolutions - C7 AJ
MIAMI BEACH
COMMISSION MEMORANDUM
TO:
FROM:
DATE:
Honorable Mayor and Members of the City Commission
Raul J. Aguila, City Attorney
July 25, 2018
SUBJECT: A RESOLUTION OF THE MAYOR AND CITY COMMISSION OF THE CITY OF
MIAMI BEACH, FLORIDA, DIRECTING THE CITY ADMINISTRATION TO
COLLECT AND TRACK, ON AN ANNUAL BASIS, SEA LEVEL RISE DATA FROM
THE VIRGINIA KEY TIDAL GUAGE AND FROM THE SOUTHEAST FLORIDA
REGIONAL CLIMATE CHANGE COMPACT (OR FROM AN ALTERNATIVE
PREFERRED DATA SOURCE, IF ONE BECOMES AVAILABLE), AND TO
ANNUALLY REPORT SUCH DATA TO THE CITY COMMISSION IN ORDER TO
FACILITATE AN INCREMENTAL ADAPTATION STRATEGY IN THE CITY.
RECOMMENDATION
Pursuant to the request of Vice-Mayor Mark Samuelian, the above-referenced Resolution is
submitted for consideration by the Mayor and City Commission at the July 25, 2018 City
Commission meeting.
Legislative Tracking
Office of the City Attorney
Sponsor
Vice-Mayor Mark Samuelian
ATTACHMENTS:
Description
D Resolution
Page 784 of 1464
SOUTH EAST FLO A
iss?
Unified Sea Level Rise Projection
Southeast Florida
I
2019 UPDATE
I
Prepared by the
Southeast Florida Regional Climate Change Compact's
Sea Level Rise Ad Hoc Work Group
Table of Contents
EXECUTIVE SUMMARY 4
INTRODUCTION 5
Impacts Associated with Sea Level Rise for Southeast Florida 5
How are Greenhouse Gas Emissions and Sea Level Rise Related? 5
Future Projections if Emissions Are Reduced 6
PURPOSE AND INTENDED USE 8
Who Should Use This Projection and Guidance Document? 8
Who Developed the Unified Sea Level Rise Projection for Southeast Florida? 8
Frequency of Future Updates 8
UNIFIED SEA LEVEL RISE PROJECTION FOR SOUTHEAST FLORIDA 9
2019 Projection and Summary 9
PROJECTION DEVELOPMENT METHODOLOGY 11
Projection Update 11
Comparison with Previous Projections 12
GUIDANCE FOR APPLICATION 13
Guidance in Applying the Projections 13
Tools Available to Visualize Sea Level Rise 15
SUMMARY 16
LITERATURE CITED 17
APPENDIX A: STATE OF SCIENCE UPDATE 21
Regional and Global Sea Level Rise Observations 21
Acceleration of Sea Level Rise 22
Factors Influencing Future Sea Level Rise 24
Effects of Greenhouse Gas Emissions 27
Consequences of Sea Level Rise 28
Unified Sea Level Rise Projection: 2019 Update 2
Recommended Citation
Southeast Florida Regional Climate Change Compact Sea Level Rise Work Group (Compact). February 2020.
A document prepared for the Southeast Florida Regional Climate Change Compact Climate Leadership
Committee. 36p.
Sea Level Rise Ad Hoc Work Group
The Southeast Florida Regional Climate Change Compact wishes to acknowledge the Work Group participants
for contributing to the development of the projection and guidance document:
Ricardo Domingues, University of Miami/National Oceanic and Atmospheric Administration*
David Enfield, Ph.D., National Oceanic and Atmospheric Administration (retired)
Nancy J. Gassman, Ph.D., City of Ft. Lauderdale
Laura Geselbracht, The Nature Conservancy
Katherine Hagemann, C.F.M., Miami-Dade County
Jake Leech, Ph.D., Palm Beach County
Jayantha Obeysekera, Ph.D., P.E., Florida International University (Chair)
Akintunde Owosina, P.E., South Florida Water Management District
Joseph Park, Ph.D., P.E., U.S. Department of Interior*
Michael Sukop, Ph.D., PG, CHg, Florida International University
Tiffany Troxler, Ph.D., Florida International University
John Van Leer, Sc.D., University of Miami
Shimon Wdowinski, Ph.D., Florida International University
Staff Liaison: Samantha Danchuk, Ph.D., P.E., Broward County
Compact Staff Support: Lauren Ordway, Institute for Sustainable Communities
* Staff participation from federal agencies does not necessarily imply official review or opinions of their agencies.
The Compact also wishes to express its appreciation to those whom provided technical guidance in the early
phase of the process to support the recommendations of the Work Group:
Andrea Dutton, Ph.D., University of Wisconsin
John Hall, Ph.D., Bureau of Land Management
Robert E. Kopp, Ph.D., Rutgers University
Glenn Landers, P.E., U.S. Army Corps of Engineers*
Mark Merrifield, Ph.D., Scripps Institution of Oceanography at the University of California San Diego
Gary Mitchum, Ph.D., University of South Florida
William Sweet, Ph.D., National Oceanic and Atmospheric Administration
Philip R. Thompson, Ph.D., University of Hawaii
Chris Weaver, Ph.D., Environmental Protection Agency
Participants contributed information, engaged in group meetings and/or online discussions, and helped develop or
review portions of the group report. Participation by these individuals does not necessarily imply personal or agency
agreement with the complete findings and recommendations of this report.
Unified Sea Level Rise Projection: 2019 Update 3
Executive Summary
Early in the Southeast Florida Regional Climate Change Com pact's ("the Compact") work together, Broward,
Miami-Dade, Monroe, and Palm Beach counties recognized the need to unify a diversity of local sea level rise
projections to create a single, regionally unified projection, ensuring consistency in adaptation planning and
policy, and infrastructure siting and design in the Southeast Florida four-county region. The Compact published
the first Regionally Unified Sea Level Rise Projection for Southeast Florida in 2011, and updated the projection
in 2015. This document, the Compact's third Regionally Unified Sea Level Rise Projection, provides an update
to the amount of anticipated sea level rise in Southeast Florida through 2120. These projections represent a
consensus from a technical Work Group consisting of members from the academic community and federal
agencies, with support from local government staff, and incorporates the most up-to-date, peer-reviewed
literature, and climate modeling data. The Projection supports local government, regional entities, and other
partners in understanding vulnerabilities associated with sea level rise and informs the development of science-
based adaptation strategies, policies, and infrastructure design.
The 2019 Projection is based on projections of sea level rise developed by the Intergovernmental Panel on
Climate Change (IPCC) Fifth Assessment Report (IPCC, 2014), as well as projections from the National Oceanic
and Atmospheric Administration (NOAA) (Sweet et al., 2017), and accounts for regional effects, such as
gravitational effects of ice melt, changes in ocean dynamics, vertical land movement, and thermal expansion
from warming of the Florida Current that produce regional differences in Southeast Florida's rate of sea level
rise compared to global projections.
Based on past and current emissions, all projection curves assume a growing greenhouse gas emission
concentration scenario, in which emissions continue to increase until the end of the century, consistent with
the IPCC Fifth Assessment Report's (ARS) Representative Concentration Pathways (RCP 8.5). Estimates of sea
level rise are provided from a baseline year of 2000, and the planning horizon has been extended to 2120, in
response to the release of climate scenarios extending beyond the year 2100 by federal agencies (NOAA and
the U.S. Army Corps of Engineers) and the need for planning for infrastructure with design lives greater than 50
years.
In the short term, sea level rise is projected to be 1 O to 17 inches by 2040 and 21 to 54 inches by 2070 (above
the 2000 mean sea level in Key West, Florida). In the long term, sea level rise is projected to be 40 to 136 inches
by 2120. Projected sea level rise, especially beyond 2070, has a significant range of variation as a result of
uncertainty in future greenhouse gas emissions reduction efforts and resulting geophysical effects.
The 2019 Unified Sea Level Rise Projection includes three curves for application, in descending order, the
NOAA High Curve, the NOAA Intermediate High Curve, and the curve corresponding to the median of the
Intergovernmental Panel on Climate Change (IPCC) ARS RCP 8.5 scenario. A fourth curve, the NOAA Extreme
curve, is included for informational purposes, not for application, illustrating the possible upper limit of
sea level rise in response to potential massive ice sheet collapse in the latter part of the century. This curve
underscores that without imminent and substantial reductions in greenhouse gas emissions, much greater sea
level rise is possible more than 100 years from now.
This guidance document describes the recommended application of the projection as it relates to both high-
and low-risk projects and short- and long-term planning efforts. The Work Group recommends that this
guidance be updated, at a minimum every five years to reflect the ongoing advances in scientific knowledge
related to global climate change and potential impacts.
Unified Sea Level Rise Projection: 2019 Update 4
Introduction
IMPACTS ASSOCIATED WITH SEA LEVEL RISE FOR SOUTHEAST FLORIDA
The climate is changing, manifesting in significant impacts for the Southeast Florida region, including increasing
average temperatures, more intense storm events, and rising sea levels. Sea level rise, caused by the thermal
expansion of warming ocean water and melting land ice as the earth warms, is one of the most evident impacts
in our region given Southeast Florida's low-lying elevation and porous geology.
The consequences associated with sea level rise are already apparent in Southeast Florida and pose an
immediate and real threat to lives, livelihoods, economies, and the environment. Consequences include
physical impacts such as coastal inundation and erosion, increased frequency of flooding in vulnerable coastal
areas as well as inland areas due to impairment of the region's largely gravity-driven stormwater infrastructure
system, reduced soil infiltration capacity, and saltwater intrusion of drinking-water supply. Moreover, the
impacts of surge from tropical storms or hurricanes are exacerbated as a result of sea level rise. Increased
pollution and contamination as a result of flooding degrades natural resources critical to the region's economy.
Consequences also include cascading socio-economic impacts such as displacement, decrease in property
values and tax base, increases in insurance costs, loss of services and impairment of infrastructure such as
roads and septic systems. Appendix A: State of the Science, describes the interconnected processes and
resulting impacts of sea level rise in additional detail.
The extent of these impacts into the future is dependent upon the factors influencing the rate of sea level rise
such as thermal expansion of oceans and increased rate of melting of land-based ice sheets due to global
warming, the degree to which society limits greenhouse gas emissions in the near-term, and the decisions
and investments made by communities to increase their climate resilience. One of the values of the Unified
Sea Level Rise Projection is its application for scenario testing to better understand the potential impacts and
ti meline of sea level rise within the Southeast Florida community.
OBSERVED SEA LEVEL RISE IN SOUTHEAST FLORIDA
Global mean sea level (GMSL) during 2018 was the highest annual average in the satellite altimetry record
(1993-2018), rising approximately 3 inches above the 1993 average (Thompson et al., 2019). Projections
anticipate an increase in the acceleration of sea level rise regionally based on recent observations in response
to changes in the speed and thermodynamics of the Florida Currents and Gulf Stream (Domingues et al., 2018;
Sweet et al., 2017; Volkov et al., 2019). Based on the 5-year moving average, the observed sea level rise at the
Key West tide gauge from 2000 to 2017 is 3.9 inches. Whether this rapid rise will be persistent into the future is
unclear at this time.
HOW ARE GREENHOUSE GAS EMISSIONS AND SEA LEVEL RISE RELATED?
Since the beginning of the Industrial Revolution, human activities have caused significant increases in emissions
of greenhouse gases in the atmosphere, such as carbon dioxide, methane, and nitrous oxides in addition
to natural emissions of these gases due to the biome carbon and nitrogen cycles. Major sources of carbon
dioxide are the burning of fossil fuels such as coal, petroleum-based liquid fuels, and natural gas for electric
Unified Sea Level Rise Projection: 2019 Update 5
power generation, transportation, and industrial processes. These greenhouse gases trap heat from the
sun in a natural process called the "greenhouse effect," which would otherwise be radiated back to space.
Problematically, as the concentrations of these gases accumulate in the earth's atmosphere as a result of
human activities, the earth's average temperature continues to rise. This process is called "global warming."
More than 90% of the warming that has happened on Earth over the past 50 years has been transferred to
the ocean. Sea level rise is a result of both the expansion of seawater as the ocean temperature increases, as
well as the melting of glaciers and ice sheets. As a result of continuing global warming, the rate of sea level rise
accelerates with passing time.
FUTURE PROJECTIONS IF EMISSIONS ARE REDUCED
The rate of sea level rise projected, particularly in the latter half of the century, is dependent upon the amount
of greenhouse gas emissions generated in the next decade and sustained in the coming decades. Rapid and
immediate global, federal, state, local, and individual action will be necessary to limit the amount of sea level
rise adaptation required. The four greenhouse gas concentration scenarios, known as the Representative
Concentration Pathways (RCPs) are sets of scenarios for greenhouse gas emissions dependent upon
reduction commitments, economic activity, energy sources, population, and land use trajectories, and other
socio-economic factors. RCPs are input into climate models which yield sea level rise scenarios. The lowest
concentration scenario, RCP 2.6, is viewed as the scenario necessary to keep global temperature increases
below 2ºC and slow the rate of sea level rise (van Vuuren et al 2011 a). This scenario would require that
greenhouse gas emissions peak around 2020 and decrease at 4% annually (van Vuuren et al., 201 1a). Future
global mean sea level would be significantly lower for RCP 2.6 compared to that of RCP 8.5 (4PCC, 2019). The
types of reduction strategies necessary to reduce regional emissions can be found in the Compact's Regional
Climate Action Plan (www.rcap2.org).
Unified Sea Level Rise Projection: 2019 Update 6
WHAT ARE RCPS?
The future impacts of climate depend not only on the
response of our Earth system, but also on how global
society responds through changes in technology,
economy, policy, and lifestyle. These responses are
uncertain, so future scenarios are used to explore the
consequences of different options. Representative
Concentration Pathways (RCPs) are possible
future scenarios for greenhouse gas emissions, or
concentration pathways, used within the IPCC ARS
and other complex climate modeling activities that
simulate how the climate might change in the future.
There are generally four of these scenarios used in
climate modeling: RCP 8.5, RCP 6, RCP 4.5, and RCP
2.6. The numbers in each RCP refers to the amount
of radiative forcing produced by greenhouse gases
in 2100, which is a measure of the energy absorbed
and retained by the lower atmosphere. For example,
in RCP 8.5 the radiative forcing is 8.5 watts per meter
squared (W/m?) in 21 OO.
RCPs start with atmospheric concentrations of
greenhouse gases rather than socioeconomic
processes (van Vuuren et al., 2011 b).This is important
because every modelling step from a socioeconomic
scenario to climate change impacts adds uncertainty.
That said, these concentration pathways are
dependent upon reduction commitments, economic
activity, energy sources, population, land use
trajectories, and other socio-economic factors that
could lead to a particular concentration pathway and
magnitude of climate change.
RCP 2.6 RCP 4.5 RCP 6 RCP 8.5
Greenhouse gas Very low Medium-low Medium baseline; High baseline
emissions mitigation high mitigation
Very low baseline
Agricultural area Medium for cropland Very low for both Medium for cropland Medium for both
and pasture cropland and pasture but very low for cropland and pasture
pasture (total low)
Air pollution Medium-Low Medium Medium Medium-high
Main characteristics of each Representative Concentration Pathway (RCP). Vuuren et.al., 2011
RCP PRIMARY CHARACTERISTICS
» RCP 2.6 is representative of scenarios in the
literature that lead to very low greenhouse gas
concentration levels. lt is a "peak-and-decline"
scenario; its radiative forcing level first reaches a value
of around 3.1 W/m2 by mid-century, and returns to 2.6
W/m2 by 21 OO. In order to reach such radiative forcing
levels, greenhouse gas emissions (and indirectly
emissions of air pollutants) are reduced substantially,
over time (Van Vuuren et al. 2007a).
» RCP 4.5 is a stabilization scenario in which total
radiative forcing is stabilized shortly after 2100,
without overshooting the long-run radiative forcing
target level (Clarke et al. 2007; Smith and Wigley 2006;
Wise et al. 2009).
» RCP 6 is a stabilization scenario in which total
radiative forcing is stabilized shortly after 2100,
without overshoot, by the application of a range of
technologies and strategies for reducing greenhouse
gas emissions (Fujino et al. 2006; Hijioka et al. 2008).
» RCP 8.5 is characterized by increasing greenhouse
gas emissions over time, representative of scenarios
in the literature that lead to high greenhouse gas
concentration levels (Riahi et al. 2007).
(Characteristics quoted from van Vuuren et. al., 2011)
Unified Sea Level Rise Projection: 2019 Update
Purpose and Intended Use
WHO SHOULD USE THIS PROJECTION AND GUIDANCE DOCUMENT?
The Unified Sea Level Rise Projection for Southeast Florida and this guidance document are intended to assist
decision-makers at both the local and regional levels in Southeast Florida to plan for and make decisions
about sea level rise and associated vulnerabilities based on best-available science. The projection (Unified Sea
Level Rise Projection for Southeast Florida) contains a graph and table describing the anticipated rise in sea
level from 2000 through 2120. The projection can be used to estimate future potential sea level elevations
in Southeast Florida and the relative change in sea level from today to a point in the future. The section,
Guidance for Application, contains directions and specific examples of how the projection can be used by local
governments, planners, designers, engineers, and developers. This regional projection is offered to ensure that
all major infrastructure projects throughout the Southeast Florida region have the same basis for design and
construction relative to future sea level.
WHO DEVELOPED THE UNIFIED SEA LEVEL RISE PROJECTION FOR SOUTHEAST FLORIDA?
In 201 O, the Southeast Florida Regional Climate Change Compact first convened the Sea Level Rise Ad Hoc Work
Group (Work Group) for the purpose of developing a Unified Sea Level Rise Projection for the region. The Work
Group reviewed existing projections and scientific literature and developed a unified regional projection for the
period from 201 O to 2060 (Compact, 2012), and recommended a review of the projection four years after its
release in 2011.
In September 2014, the Sea Level Rise Work Group was reconvened to develop the second update of the
Unified Sea Level Rise Projection, based on projections and scientific literature released since 2011, which was
published by the Compact in October 2015 (Compact, 2015).
Based on guidance from the Work Group, and in response to emergent research since the publication of the
2015 report, the Compact reconvened the Work Group in 2019 to produce the third update. In particular,
new research has indicated the potential for faster rates of melting of the Antarctic Ice Sheet, triggering the
likelihood of higher rates of rise in the future. In addition, the Work Group opted to include the regional sea
level rise rates as reported in the Fourth National Climate Assessment (Sweet et al., 2017).
The Ad Hoc Sea Level Rise Work Group consists of experts within the academic community and federal
agencies, and is supported by individuals from local government and staff support to the Compact. Most of the
2019 Work Group members contributed to the previous Compact projections.
FREQUENCY OF FUTURE UPDATES
The Southeast Florida Regional Climate Change Compact is committed to updating the Unified Sea Level Rise
Projection periodically, and at a minimum every five years, to incorporate the latest scientific understanding
of climate change and sea level rise for Southeast Florida. Scientific understanding of sea level rise is rapidly
advancing, generating new, peer-reviewed literature and modeling from a variety of key sources, including
the Intergovernmental Panel on Climate Change (IPCC), the National Oceanic and Atmospheric Administration
(NOAA), and the U.S. Army Corps of Engineers (USACE), among other recognized sources. By updating this
document and the Unified Sea Level Rise Projection at least every five years, the Compact seeks to provide
ongoing and current guidance for regionally consistent sea level rise planning and decision-making.
Unified Sea Level Rise Projection: 2019 Update 8
Unified Sea Level Rise Projection for Southeast Florida
2019 PROJECTION AND SUMMARY
This Unified Sea Level Rise Projection for Southeast Florida updated in 2019 projects the anticipated range of
sea level rise for the region from 2000 to 2120 (Figure 1 ). The projection highlights three planning horizons:
1. short term: by 2040, sea level is projected to rise 1 O to 17 inches above 2000 mean sea level.
2. medium term: by 2070, sea level is projected to rise 21 to 54 inches above 2000 mean sea level.
3. long term: by 2120, sea level is projected to rise 40 to 136 inches above 2000 mean sea level.
Details of the projection development methodology appear in the next section.
The Projection is recommended to be applied in the following manner:
The blue shaded zone between the IPCC median curve and the NOAA Intermediate-High curve is
recommended to be generally applied to most projects within a short-term planning horizon (up to
2070). The I PCC median curve represents the most likely average sea level before 2070, but is not
representative of the realistic interannual and interdecadal variations that will occur with sea level
rise values within the blue shaded zone. The IPCC median curve can be used for non-critical, low risk
projects with short design lives (<50 years) that are adaptable, and have limited interdependencies
with other infrastructure or services. All other projects with design lives that end before 2070 should
consider values within the blue zone or along the NOAA Intermediate-High curve based on risk
tolerance.
For non-critical infrastructure in service during or after 2070, the NOAA Intermediate-High Curve is
recommended. Sea level rise is unlikely to exceed the NOAA Intermediate-High Curve by 21 OO.
The NOAA High curve of the projection, above the shaded zone, should be utilized for planning of
critical, high risk projects in service after 2070 or for projects which are not easily replaceable or
removable or are critically interdependent with other infrastructure or services. Examples are: major
roads and bridges, water and wastewater utilities, power plants including nuclear, major urban
developments, etc. Sea level rise is very unlikely to be higher than the NOAA High curve before 21 OO.
The NOAA Extreme curve is displayed on the Unified Sea Level Rise Projection for informational
purposes but is not recommended for design.
TABLE 1: Sea Level Rise Projection data by decadal intervals
DATUM: FEET 2000 MSL
IPCC MED NOAA2017 NOAA2017
YEAR SO% INT-HIGH HIGH
DATUM: FEET NAVD
IPCC MED NOAA2017 NOAA2017
YEAR SO% INT-HIGH HIGH
2000 0.00 o o 2000 -0.80 -0.78 -0.78
2010 0.19 0.3 0.33 2010 -0.61 -0.49 -0.45
2020 0.39 0.56 0.69 2020 -0.42 -0.22 -0.09
2030 0.63 0.98 1.18 2030 -0.17 0.2 0.4
2040 0.84 1.38 1.74 2040 0.04 0.6 0.96
2050 1.13 1.94 2.46 2050 0.33 1.15 1.68
2060 1.40 2.56 3.38 2060 0.60 1.78 2.6
2070 1.72 3.31 4.49 2070 0.91 2.53 3.71
2080 2.03 4.17 5.74 2080 1.23 3.38 4.96
2090 2.40 5.12 7.09 2090 1.59 4.34 6.3
2100 2.72 6.14 8.56 2100 1.92 5.35 7.78
2120 3.29 7.64 11.32 2120 2.49 6.86 10.54
Unified Sea Level Rise Projection: 2019 Update 9
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Unified Sea Level Rise Projection
(Southeast Florida Regional Climate Change Compact, 2019)
IPCC NOAA
Year Median Intermediate NOAA High
(inches) High (inches)
(inches) - .. -
2040 10 17 21
2070 21 40 54
2120 40 92 136
Observed
5-Year Average
Mean Sea Level
---------
175 NOAA Extreme
• / ,,,'
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• 4o e
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/
/
/
4 50 Year Planning Horizon
2000 2010 2020 2030 2040 2050 2060
Year
2070 2080 2090 2100 2110
NOAA High
92
Intermediate High
NOAA
40
2120
IPCC Median
FIGURE 1: Unified Sea Level Rise Projection
SOUTHEAST FLORIDA qa#a 4à
Ciüiü&E @e
These projections start from zero in year 2000 and are referenced to mean sea level at the Key West tide gauge. Based on the 5-year average of mean
sea level, approximately 3.9 inches of sea level rise has occurred from 2000 to 2017 (see historic sea level section of guidance document). The projection
includes global curves adapted for regional application: the median of the IPCC ARS RCP 8.5 scenario (Growing Emissions Scenario) as the lowest
boundary (solid thin curve), the NOAA Intermediate High curve as the upper boundary for short-term use until 2070 (solid thick line), the NOAA High
curve as the upper boundary for medium and long-term use (dash dot curve). The shaded zone between the IPCC ARS RCP 8.5 median curve and the
NOAA Intermediate High is recommended to be generally applied to most projects within a short-term planning horizon. Beyond 2070, the adaptability,
interdependencies, and costs of the infrastructure should be weighed to select a projection value between the IPCC Median and the NOAA High curves.
The NOM Extreme curve (dash curve) brackets the published upper range of possible sea level rise under an accelerated ice melt scenario. Emissions
reductions could reduce the rate of sea level rise significantly.
Unified Sea Level Rise Projection: 2019 Update 10
Projection Development Methodology
PROJECTION UPDATE
The key components of the methodology used to develop the Unified Sea Level Rise Projection are as follows:
Starting in 2000: The year 2000 has been selected as the initial year of the projection because of its use as the
reference year for the latest regional sea level projections published by NOAA (Sweet et al., 2017), which is the
primary source of the data used in this report. The previous projection started in 1992, based on the midpoint
of the tidal epoch from 1983 to 2001 which defined the previous elevation of mean sea level. Defining mean
sea level by a timeframe is necessary because sea level is constantly changing. A fixed elevation is necessary
to serve as a baseline for which to add sea level rise projections and to convert to elevations in other datums.
NOAA has determined a new mean sea level for 2000, the midpoint of the tidal epoch from 1991 to 2009. A
comparison of the 2015 and 2019 Unified Sea Level Rise Projection is presented in the next section.
Updated Planning Horizons: To align with a 20-year planning horizon for land use and a SO-year planning
horizon for infrastructure, the sea level rise values displayed were moved to 2040 and 2070, respectively.
Planning Horizon 0of 2120: In response to the release of climate scenarios extending beyond 2100 by federal
agencies including the US Army Corps of Engineers (USACE) and the National Oceanographic and Atmospheric
Administration (NOAA) and the need for planning for infrastructure with design lives greater than 50 years, the
Unified Sea Level Rise Projection time scale has been extended to 2120.
Tide Gauge Selection: The Key West gauge (NOAA Station ID 8724580) was maintained as the reference gauge
for calculation of the regional projection, consistent with all previous projections. In addition, appropriate
conversion calculations are provided in Section 4: Guidance for Application, in order to reference the projection
to the Miami Beach gauge (NOAA Station ID 8723170). the South Port Everglades gauge (NOAA Station ID
8722956) or the Lake Worth Pier gauge (NOAA Station 1D 8722670). The Key West gauge has recorded tidal
elevations since 1913. Tidal records from Miami Beach, South Port Everglades and Lake Worth Pier are available
since 2003, 2018 and 1996, respectively.
Updated Historic Data: Observed data from the Key West tide gauge was plotted from 1992 to 2017 based
on the mean sea level, averaged over 5-year intervals. These data were obtained from the USACE Sea Level
Tracker, https://climate.sec.usace.army.mil/slr app/.
Selection of NOAA (2017) Regional Projections and Update of /PCC Median Curve: The regional sea level
projections available from NOAA (Sweet et al., 2017) replaced two of the three previously used curves. The
selected curves are regional projections rather than previously used global projections. The NOAA Intermediate
High regional projection was selected as the upper short term boundary for typical infrastructure because of
its IPCC determination to be very likely under the RCP 8.5 emissions pathway, which aligns with current global
emissions trends. The NOAA Intermediate High regional projection also approximates the previously used
USACE High curve. The NOAA High curve was updated with its regional projection. The third curve, the IPCC
Median, was reprojected for the region (Key West) rather than global scale, using the NOAA (Sweet et al., 2017)
methodology.
Reference to NOAA Extreme Curve: The NOAA Extreme curve is displayed on the Unified Sea Level Rise
Projection for informational purposes but is not recommended for design.
Unified Sea Level Rise Projection: 2019 Update 11
COMPARISON WITH PREVIOUS PROJECTIONS
Table 2 compares values from the 2015 and 2019 Unified Sea Level Rise Projections at the planning horizons
referenced in the 2015 projection. The numeric values have been rounded for simplicity. The difference in the
reference elevation for the two projections is less than 1 inch (1992 mean sea level compared to 2000 mean
sea level) and was considered to be included in the rounding error to allow this comparison. The lowest curve,
the IPCC median, increased by 2 to 3 inches in the 2019 projection. The upper boundary of the short term
projection increased by 2 to 5 inches (for planning horizons before 2060). The NOAA High curve used for critical
infrastructure or planning horizons after 2060 increased 7 to 22 inches, the most significant change between
projections.
TABLE 2: Comparison of Unified Projection in 2015 and 2019 at Key West
2015 2019 2015 2019 2015 2019
IPCC Median IPCC Median USACE High NOAA NOAA High NOAA High
Global Regional (inches) lnermediate (inches) (inches)
(inches) (inches) High (inches)
2030 6 8 10 12 12 14
2060 14 17 26 31 34 41
2100 31 33 61 74 81 103
Note: The NOM Extreme curve values are not included in the table because there was not a comparable curve in the
2015 projection.
Unified Sea Level Rise Projection: 2019 Update 12
Guidance for Application
GUIDANCE IN APPLYING THE PROJECTIONS
Audiences
The Unified Sea Level Rise Projection for Southeast Florida is intended to be used for planning purposes by a
variety of audiences and disciplines when considering sea level rise in reference to both short- and long-term
planning horizons as well as infrastructure siting and design in the Southeast Florida area. Potential audiences
for the projections include, but are not limited to, elected officials, urban planners, architects, engineers,
developers, resource managers, and public works professionals.
One of the key values of the projection is the ability to associate specific sea level rise scenarios with timelines.
When used in conjunction with vulnerability assessments, these projections inform the user of the potential
magnitude and extent of sea level rise impact at a general timeframe in the future. The blue shaded portion
of the projection provides a likely range for sea level rise values at specific planning horizons. Providing
a range instead of a single value may present a challenge to users such as engineers who are looking to
provide a design with precise specifications. Public works professionals and urban planners need to work
with the engineers and with policymakers to apply the projection to each project based on the nature, value,
interconnectedness, and life cycle of the infrastructure proposed.
Finally, elected officials should use the projections to inform decision-making regarding adaptation policies,
budget impacts associated with design features that address future sea level rise, capital improvement projects
associated with drainage and shoreline protection, and land use decisions.
Applying Projection Curves to Infrastructure Siting And Design
When determining how to apply the projection curves, the user needs to consider the nature, value,
interconnectedness, and lifespan of the existing or proposed infrastructure. An understanding of the risks
that critical infrastructure will be exposed to throughout its life cycle such as sea level rise inundation, storm
surge, and nuisance flooding and a plan for adaptation must be established early in the conceptual phase.
A determination must be made on whether or not threats can be addressed mid-life cycle via incremental
adaptation measures, such as raising the height of a sluice gate on a drainage canal. If incremental adaptation
is not possible for the infrastructure proposed and inundation is likely, designing to accommodate the
projected sea level rise at conception or selection of an alternate site should be considered. Forward thinking
risk management is critical to avoiding loss of service, loss of asset value, and most importantly loss of life or
irrecoverable resources. The guidance in the following paragraphs can be considered for selection of curves
from the projection for project applications.
Unified Sea Level Rise Projection: 2019 Update 13
>> Application of the IPCC Median Curve
The IPCC Median or lower blue shaded portion of the projection can be applied to most infrastructure projects
before 2070 or projects whose failure would result in limited consequences to others. An example low risk
projects may be a small culvert in an isolated area. The designer of a type of infrastructure that is easily
replaced, has a short lifespan, is adaptable, and has limited interdependencies with other infrastructure or
services must weigh the potential benefit of designing for higher sea level rise with the additional costs. Should
the designer opt for specifying the lower curve, she/he must consider the consequences of under-designing for
the potential likely sea level condition. Such consequences may include premature infrastructure failure.
>> Application of the NOAA Intermediate High Curve
Projects in need of a greater factor of safety related to potential inundation should consider designing for
the NOAA Intermediate High Curve. Examples of such projects may include evacuation routes planned for
reconstruction, communications and energy infrastructure, and critical government and financial facilities or
infrastructure that may stay in place beyond a design life of 50 years.
>> Application of the NOAA High Curve
Due to the community's fundamental reliance on major infrastructure, existing and proposed critical
infrastructure should be evaluated using the NOAA High curve. Critical projects include those projects which
are not easily replaceable or removable, have a long design life (more than 50 years), and are interdependent
with other infrastructure or services. If failure of the critical infrastructure would have catastrophic impacts,
it is considered to be high risk. Due to the community's critical reliance on major infrastructure, existing and
proposed high risk infrastructure should be evaluated using the NOAA High curve. Examples of high risk critical
infrastructure include nuclear power plants, wastewater treatment facilities, levees or impoundments, bridges
along major evacuation routes, airports, seaports, railroads, and major highways.
Unified Sea Level Rise Projection: 2019 Update 14
Projection Referenced to the North American Vertical Datum
The Unified Sea Level Rise Projection referenced to the North American Vertical Datum (NAVD) is shown in
Figure 2 and summarized in Table 3. Each NOAA tide gauge in the region has published datums that can be
used for conversions between elevations (https://tidesandcurrents,noaa.gov/datums.html?id=8724580).
FIGURE 2: Unified Sea Level Rise Referenced to NAVO
14
13
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], unified sea Level Rise Projection
(Southeast Florida Regional Climate Change Compact, 2019)
IPCC NOAA
Year t „lt Intermediate vu1at High (Feet IAVD) (Feet IAVD)
2040 o 0.6
2070 0.9 2.5
2120 2.5 6.9
NOAA High
(Feet NAVD)
1
37
10.5
"%7war-
,,,,,
/ 10.5 » NOAA High
,/ ,,,,,.-✓
/
/
' .- e 3.7. « 2.s
6.9 · Intermediate High
NOAA
IPCC Median
5-Year Average of
Mean Sea Level
• e-e
1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110 2120
Year
TABLE 3: Unified Sea Level Rise Projection Referenced to NAVO
UNIFIED SEA LEVEL RISE PROJECTION
(Southeast Florida Regional Climate Change Compact. 2019)
Year IPCC Median NOAA Intermediate NOAA High
(Feet NAVO) High (Feet NAVO) (Feet NAVD)
2040 o 0.6
2070 0.9 2.5 3.7
2120 2.5 6.9 10.5
Referencing to Today's Sea Levels
Based on the 5-year average of mean sea level at Key West, sea level rose approximately 3.9 inches from 2000
to 2017 (NOAA, 2020). This value of 3.9 inches can be subtracted from the rise projected in Table 1 to obtain an
estimate of how much sea level will rise from the 2017 mean sea level. Note the availability of computed values
for the 5-year average of mean sea level will always be delayed as a function of needing to have 2.5 years data
past the date in order to compute the average.
To compute the rise expected from any future date relative to the existing sea level, the linear trend should be
computed and its slope should be multiplied by the number of years that have passed since 2000. Based on a
linear trend analysis of the historic record at Key West, sea level has risen at a rate of approximately 0.1 inches
Unified Sea Level Rise Projection: 2019 Update 15
per year. Note this linear trend will change as more data are collected by the tide gauge. Also, when the slope
of the linear trend line changes, the computed amount of rise will change. Care should be taken to consider the
computation methodology before comparing statements of relative sea level rise for a distinct time period.
TOOLS AVAILABLE TO VISUALIZE SEA LEVEL RISE
The observed data and NOAA curves included in the projection can be reproduced using the USACE Sea Level
Rise calculator and USACE Sea Level Tracker https://
climate.sec.usace.army.mil/slr_app/. Inundation from sea level rise can be visualized by using the Florida Sea
Level Sketch Planning Tool
Unified Sea Level Rise Projection: 2019 Update 16
Summary
The Work Group recommends the use of the NOAA High curve, the NOAA Intermediate High curve, and
the median of the IPCC ARS RCP 8.5 scenario (IPCC, 2013) as the basis for a Southeast Florida sea level rise
projection for the 2040, 2070 and 2120 planning horizons. In the short term, mean sea level rise is projected to
be 1 O to 17 inches by 2040, and 21 to 54 inches by 2070 (above the 2000 mean sea level).
Both mean and annual average of sea level exhibit significant variability over time and that should be
considered when using the projections. Annual average of sea level at the Key West gauge has risen
approximately 3.9 inches from 2000 to 2017 (which is much larger than the linear trend-derived rate of rise
reported by NOAA). Whether this rapid rise will be persistent into the future is unclear at this time.
In the long term, sea level rise is projected to be 40 to 136 inches by 2120. The IPCC Median or lower blue
shaded portion of the projection can be applied to most infrastructure projects before 2070 or projects
whose failure would result in limited consequences to others. Projects in need of a greater factor of safety
related to potential inundation should consider designing for the NOAA Intermediate High Curve. For critical
infrastructure projects with design lives in excess of 50 years, use of the NOAA High curve is recommended
with planning values of 54 inches in 2070 and 136 inches in 2120. Sea level will continue to rise even if global
mitigation efforts to reduce greenhouse gas emissions are successful at stabilizing or reducing atmospheric
CO2 concentrations; however, emissions mitigation is essential to moderate the severity of potential impacts
in the future. A substantial increase in sea level rise within this century is likely and may occur in rapid pulses
rather than gradually.
The recommended projection provides guidance for the Compact Counties and their partners to initiate
planning to address the potential impacts of sea level rise in the region. The shorter-term planning horizons
(through 2070) are critical to implementation of the Southeast Florida Regional Climate Change Action Plan, to
optimize the remaining economic life of existing infrastructure, and to begin to consider adaptation strategies.
As scientists develop a better understanding of the factors and reinforcing feedback mechanisms impacting
sea level rise, the Southeast Florida community will need to adjust the projections accordingly and adapt to the
changing conditions. To ensure public safety and economic viability in the long run, strategic policy decisions
will be needed to develop guidelines to direct future public and private investments to areas less vulnerable to
future sea level rise impacts.
Unified Sea Level Rise Projection: 2019 Update 17
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Unified Sea Level Rise Projection: 2019 Update 19
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Unified Sea Level Rise Projection: 2019 Update 20
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Unified Sea Level Rise Projection: 2019 Update 21
Appendix A: State of Science Update
REGIONAL AND GLOBAL SEA LEVEL RISE OBSERVATIONS
Historic Sea Level Rise in Southeast Florida
Based on the 5-year average of mean sea level, approximately 3.9 inches of sea level rise has occurred from
2000 to 2017. Figure A-1 shows the rise of sea level as observed in Key West for the time period from 1913 to
2020 and includes the monthly mean sea level data, the 5-year average of mean sea level and a linear trendline
through the monthly mean sea level. The linear trend does not match the monthly mean sea level data well. The
linear trend suggests sea level rose only 2 inches from 2000 to 2019, which is less than the 5-year average trend
analysis from 2000 to 2017 shown (NOAA, 2020). The 5-year average of the monthly mean sea level illustrates
the variability in sea level throughout the time period and highlights the continued increase in sea level above
the linear trend in the last decade.
15
10
-10
······ .. ,- I I II
"l¥'f' I
-15
1910
2000-2017: 3.9"
1992-2000: 0.2"
1915-2017: 10.7"
1920
- Mean Sea Level
Mean Sea Level 5-Year Average
•• .... Linear (Mean Sea Level )
1930 1940 1950 1960 1970 1980
Year
1990 2000 2010 2020
FIGURE A-1. Relative Sea Level Rise in Key West, Florida (NOAA Station ID 8724580) presented as monthly
mean sea level, 5-year average of monthly mean sea level and linear trend of monthly mean sea level.
Annotated measurements on right of figure are computed by subtracting the 5-year average mean sea levels
for the years listed. Sea level rise computed based on the linear trend will differ from the 5-year mean sea level
trend shown.
As discussed in the following sections describing the factors influencing sea level rise, the changing climate
will drive new nonlinear trends in sea level that deviate from historic trends, hence the need for the Unified
Projection. Although significant changes in sea level trends are anticipated over the coming decades, a
preliminary comparison of the Unified Projection and the available measured data is presented in Figure A-2.
The 5-year average mean sea level was observed to track between the IPCC Median and NOAA Intermediate
High curves from 2013 to 2017 (2017 was the last year of computable 5-year average at the time of publication).
Unified Sea Level Rise Projection: 2019 Update 22
Monthly mean sea level was observed to exceed the NOAA Intermediate High curve in almost every tidal cycle
since 2000. For additional context, the linear trend based on historic data included in Figure A-1 remains below
the IPCC Median curve from 2007 onward and below the 5-year average of mean sea level from 201 O onward.
-8
Year
MSL -MSL 5-Year Average NOAA Intermediate High IPCC Median
FIGURE A-2. Comparison of the Unified Sea Level Rise Projection from 2000 to 2020 and Relative Sea
Level Rise in Key West, Florida from 1990 to 2020. Monthly mean sea level and the 5-year average of monthly
mean sea level are based on measurements from NOAA Station ID 8724580.
Unified Sea Level Rise Projection: 2019 Update 23
ACCELERATION OF SEA LEVEL RISE
Dangendorf et al, (2017) produced a global mean sea level reconstruction for the 21st century incorporating
up-to-date observations of vertical land motion and corrections for local gravitational changes resulting from
ice melting and terrestrial freshwater storage. Their results provided a global sea level rise rate of 1.1 ± 0.3
millimeter per year before 1990 that is below previous estimates, and a rate of 3.1 ± 1.4 millimeter per year
from 1993 to 2012 that is consistent with independent estimates from satellite altimetry.
Global Mean Sea Level Change
200
15o s
2> : = o 100 = <
Adjusted Tide Gauge Data
Satellite Radar Altimetry
0.6 mm/yr
( 1900-1930) 50
(9 4/"
1900 1920 1940 1960 1980 2000 2020
FIGURE A-3. Global mean sea level change from 1900 to 2019 and increasing acceleration rates (modified
by Hansen et al., (2015) from Church and White (2011) and Hay et al., (2014). 1993 to 2019 data distributed by
AVISO+ (https://www.aviso.altimetry.fr) with support from CNES.
Recent analyses of tide gauge records acquired along the United States Atlantic coast indicate year-to-year
acceleration in the rate of sea level rise (Sweet et al., 2017). During 2010-2015, accelerated sea level rise at rates
five times the global average was observed between Key West and Cape Hatteras (Valle-Levinson, 2017), and
is attributed to the warming of the Florida Current (Domingues et al., 2018). Locally, Wdowinski et al. (2016)
analyzed the Virginia Key tide gauge record (near Miami) and found a significant acceleration in the rate of
sea level rise since 2006. The average rate of regional sea level rise since 2006 was 9±4 millimeters per year,
significantly higher than the global average rate, which has been estimated to be in the range of 4-5 millimeters
per year for the post-2006 period (WMO, 2019). The global and regional processes driving sea level rise and its
acceleration are discussed in the following sections.
NOAA Sea Level Rise Scenarios
For the Compact 2019 projections, the workgroup referenced the technical information provided in the NOM
report (Sweet et al., 2017) which was also used as input to the sea level rise chapter of the National Climate
Assessment (NCA) (httpS:/science2017.globalchange.gov/chapter/12/). The sea level projections in the NOAA
report were developed by a Federal lnteragency Sea Level Rise Task Force and they included six scenarios
(Table A-1 below) using a risk-based framing approach to deal with uncertainties. The scenario approach
is similar to the regional sea level rise scenarios produced by Hall et al. (2016) and they are linked to the
greenhouse gas emission scenarios, RCP 2.6, 4.5, and 8.5 as shown in Table A-1. The NOM 2017 report includes
the best available research since the production of the Compact 2015 report and is considered to be a reliable
source of data from the national effort on sea level rise projections. More importantly, the projections are
Unified Sea Level Rise Projection: 2019 Update 24
available regionally and that allowed the work group to customize 2019 projections using the Key West gauge as
was done for the 2015 projections.
TABLE A-1: Interpretations of the lnteragency Global Mean Sea Level (GMSL) rise scenarios (National
Climate Assessment (NCA), Chapter 12)
SCENARIO INTERPRETATION
Low Continuing current rate of GMSL rise, as calculated since 1993
Low end of very likely range under RCP 2.6
Intermediate-Low Modest increase in rate
Middle of likely range under RCP 2.6
Low end of likely range under RCP 4.5
Low end of very likely range under RCP 8.5
Intermediate High end of very likely range under RCP 4.5
High end of likely range under RCP 8.5
Middle of likely range under RCP 4.5 when accounting for possible ice cliff
instabilities
Intermediate-High Slightly above high end of very likely range under RCP 8.5
Middle of likely range under RCP 8.5 when accounting for possible ice cliff
instabilities
High High end of very likely range under RCP 8.5 when accounting for possible ice cliff
instabilities
Extreme Consistent with estimates of physically possible "worst case"
In general, the global sea level rise pathways for different emission scenarios are not very different until
about the mid-century after which they deviate significantly (e.g. Figure 4.2, IPCC 2019). The broad range of
sea level rise projection during the latter part of the century reflects the significant uncertainty in predicting
the contributions of individual sea level rise components, attributable primarily to ice cliff instability. Driven
by the desire to capture the potential for larger sea level rise resulting from rapid melting from the ice sheets
towards the latter part of the century, the work group made a decision to select higher scenarios that are also
consistent with the growing emission scenario, RCP 8.5. Recent sea level rise guidance from the Tampa Bay
Region recommended the use of RCP 8.5"...until the private and public sectors make meaningful efforts to reduce
greenhouse gas emissions." Consequently, the Intermediate High, and High scenarios (Table A-1) were included
in the 2019 scenarios set. Consistent with the 2015 projections, IPCC Median scenario for RCP 8.5 was added
to define the lower boundary of the range. The IPCC Median (with a Global Mean Sea Level, GMSL, rise of 0.73
meters) lies between Intermediate Low (0.5 meter of GMSL) and Intermediate (1 meter GMSL) scenarios in the
NOAA 2017 set (Table A-1). The Work Group also included the NOAA 2017 Extreme Scenario as an estimate of
the upper bound of what could happen as a result of a catastrophic ice sheet collapse and the primary intent of
this inclusion was to emphasize what could happen to GMSL if the emissions were allowed to continue without
mitigation.Inclusion of such an extreme scenario is not unprecedented. For instance, New York City (Gornitz
et al., 2019) included a new, physically plausible, upper-end scenario dubbed ARIM (Antarctic Rapid Ice Melt)
scenario for this purpose. The California guidance also includes a similar scenario, called H++ which reflects
extreme sea level but with unknown probability.
Unified Sea Level Rise Projection: 2019 Update 25
FACTORS INFLUENCING FUTURE SEA LEVEL RISE
Global Processes
Thermal expansion
Warming of oceans leads to a lower density and as a consequence volume per unit mass increases. The ocean
has absorbed more than 90% of the heat that is generated by heat trapping greenhouse gasses making the
thermal expansion a significant component of the observed sea level rise. Thermal expansion is expected to
increase, but its contribution to the global sea level rise may be exceeded by the increased contributions from
melting land-based ice sheets.
Acceleration of Ice Melt
Accelerated melting of glaciers and ice sheets of Greenland and Antarctica has become the predominant
factor affecting sea level rise acceleration (Oppenheimer et al., 2019). Melting is caused by anthropogenic
forcing leading to increasing temperatures and warming of the atmosphere, warm currents moving along the
coast of Greenland, and warm ocean water moving under and up into ice sheets through deep outlet glacial
fjords in Greenland and Antarctica in response to meteorologic changes. The rate of melt of the Greenland
Ice Sheet was relatively stable in the 1990s and has increased since then to a rate seven times greater than in
1992 (IMBIE, 2019; Chen et al., 2017). The rate of acceleration peaked in 2011, slowed in response to cooler
conditions until 2016, but has begun increasing again. Although all of the ice melt processes are not fully
represented in the climate projection models, studies suggest contributions from ice melt are likely to match
the estimates of melt from the IPCC ARS RCP 8.5 scenario (Oppenheimer et al., 2019).
Based on geologic records from the last two pre-historical periods that the Greenland and Antarctica ice
sheets melted, global mean sea level likely rose 18 to 27 feet in response, but potentially as much as 75 feet.
Models and analyses cannot yet confirm if similar rates of pre-historic rise will occur in response to melt in the
future (Oppenheimer et al., 2019). The possibility of such extreme rise in response to ice melt prompted the
inclusion of the NOAA Extreme curve for reference in the Unified Sea Level Rise Projection and to highlight the
importance of greenhouse gas mitigation. Although unlikely and not appropriate for infrastructure planning,
the Work Group wanted to acknowledge the evolving science in projecting accelerating ice melt and bracket the
uncertainty in rise at the end of the century based on the most recent observations and models.
Thawing Permafrost
Frozen soils are both a major source of emissions today, and a major sink for carbon during past ice ages.
Permafrost is permanently frozen soil, which holds vast amounts of organic material in a suspended state
of decay. It is found in vast, remote and inaccessible places: under tundra's covered active layer (seasonally
melted mud), underwater, and under sea ice and/or snow. It is the least understood, but potentially one of
the most important climate change drivers. Satellite remote sensing is less useful in its direct observation of
permafrost, compared to other phenomena important to sea level rise. But the high atmospheric methane
concentration in the atmosphere above the northern polar region stands out above other regions on earth.
Russian, Alaskan and other scientists from around the world are actively investigating the potential for
significant additional emissions of carbon dioxide and methane from thawing permafrost (Shakova et al., 2019).
Prior to the last three decades, heavy multi-year sea ice protected solid frozen permafrost, and the methane
sequestered within it as massive subaqueous methane hydrate deposits. Release of this methane could
constitute a powerful tipping point for atmospheric warming, and the glacial melting to follow. It is unknown
when such a tipping point is likely to occur, but the continued acceleration of global warming with business as
usual, RCP 8.5, puts us on a dangerous trajectory.
Unified Sea Level Rise Projection: 2019 Update 26
Regional/ Local Processes
Distinct rates of sea level rise recorded along the U.S. East Coast are currently largely modulated by the effect
of various regional and local processes (Piecuch et al., 2018). The long-term regional sea level rise projections
employed in this report are primarily based on the recent scenarios convened by the Sea Level Rise and Coastal
Flood Hazard lnteragency Task Force (Sweet et al., 2017), which explicitly consider these effects from regional
drivers. As an example, regional drivers may account for an additional 37 centimeters of sea level rise by 2100
in Key West under the assumptions linked with the NOM Intermediate-High scenario, totaling 1.87 meters of
sea level rise compared with 1.5 meters globally. The following section describes the most important regional
drivers that can affect rates of sea level rise in Southeast Florida.
Vertical Land Movement
Vertical earth movements (subsidence or uplift), which regionally and locally modify the averaged rate of
sea level change, result in a relative rate of change that varies from one location to another. These land
movements are inferred from historical tide data and geodesic measurements. When added to projected
rates of mean sea level rise, the vertical land movement results in a perceived rates of sea level rise change
ranging from increased rise in regions of subsidence (e.g., New Orleans) to falling sea levels where the land is
being uplifted (e.g., along the northern border of the Gulf of Alaska). Sea level rise in geologically stable regions
have only small differences with respect to the global rate of rise. Some of the processes leading to vertical
land movement include the post-glacial rebound (known as Glacial Isostatic Adjustment GIA), sediment
compaction, dam retention, and groundwater and oil withdrawal.
A robust method for estimating vertical land movements is based on continuous GPS measurements conducted
at selected locations. Over the past two decades, more than 60 continuous GPS stations were constructed
and operated in Florida by federal and state institutes, including the Continuously Operating Reference
(COR) network, US Coast Guard, Florida Department ofTransportation, and others. The length of record in
these stations vary from one to fourteen years, reflecting the difficulties in maintaining smooth operation
of a continuous GPS station. The continuous GPS measurements indicate that vertical land movements in
Florida are fairly small; they vary in the range of ±4 millimeters/year. In South Florida, in general, coastal land
elevations are considered relatively stable-meaning that the land is not experiencing significant uplift or
subsidence. Therefore, the processes listed above are likely not playing a major role on the current sea level
rise rates observed in Southeast Florida. It is important to note, however, that the vertical land movement that
is occurring is non-uniform across South Florida, and movement measured at specific monitoring stations sites
may not reflect vertical land movement in adjacent areas.
Ocean Dynamics, Gulfstream/ Circulation
Regional patterns of sea level change are partly due to trends in ocean currents, redistribution of temperature
and salinity, and atmospheric pressure. The reasons for changes in "Ocean Dynamics" are well known (Hall
et al., 2016). Thermal expansion changes the elevation of the sea surface non-uniformly and to balance the
resulting pressure gradient, ocean mass will flow from areas of large water depths into shallower continental
shelf areas (Hall et al. 2016; Yin et al. 2009). Long-term changes in ocean dynamics still represent one of the
largest sources of uncertainty for long-term projections of sea level rise (Kopp et al., 2014; Chen et al., 2019),
and current observations show only a modest decline in the strength of the Florida Current flow.
Ocean circulation has changed little during the current period of scientific observation, but in the future it may
considerably alter the relative rate of sea level rise in some regions, including Southeast Florida. The potential
slowing of the Florida Current and Gulf Stream could result in a more rapid sea level rise along the east coast
of North America. By 2100, these circulation changes could contribute an extra eight inches of sea level rise in
Unified Sea Level Rise Projection: 2019 Update 27
New York and three inches in Miami according to Yin et al. (2009). Most of the global climate models used by
the IPCC (IPCC, 1913 project a 20-30% weakening of the Atlantic Meridional Overturning Circulation (AMOC), of
which the Gulf Stream and Florida Current are a part, a response to warming caused by increasing greenhouse
gases. Measurements of the AMOC have yet to conclusively detect the beginning of this change, however there
has been a report of a recent decline in AMOC strength by Smeed et al. (2014) that coincides with the mid-
Atlantic hotspot of sea level rise reported by Ezer et al. (2013) and Rahmstorf et al. (2015). Recent analysis of
the Florida Current transport has detected only a slight decrease in circulation over the last decades. Assuming
the long-term slowdown of the AMOC does occur, sea level rise along the Florida east coast could conceivably
be as much as twenty centimeters (eight inches) greater than the global value by 21 OO. Given that changes in
ocean dynamics, such as these changes projected for the AMOC, are still one of the main sources of uncertainty
for long-term regional sea level rise scenarios (e.g. Kopp et al., 2014; Piecuch et al., 2018), longer records of
the Florida Current and Gulf Stream transport are required to confirm if the long-term decline in the strength
of the flow persists, or if it is associated with interannual/decadal natural variations. Recent regional sea level
rise scenarios for the U.S. coasts have been made available by the Sea Level Rise and Coastal Flood Hazard
lnteragency Task Force (Sweet et al., 2017), and explicitly consider regional effects of changes in ocean dynamics
and other local contributors, as described above.
Regional Ocean Heat Content Changes
Recent studies revealed accelerated rates of year-to-year changes in regional sea level variability along the U.S.
East Coast (Valle-Levinson et al., 2017). Even though these variations are not necessarily linked with long-term
sea level rise trends, these accelerated changes currently contribute to flooding conditions often observed at
Southeast Florida communities. Analysis showed that accelerated sea level rise recently observed for Southeast
Florida from 201 O to 2015 were in fact associated with thermal expansion from warming of the Florida Current
during the same time period, as reported in Domingues et al., (2018). Further analysis (Volkov et al., 2019)
revealed that such warming was linked to large-scale heat convergence within the North Atlantic subtropical
gyre caused by changes in the Atlantic Meridional Overturning Circulation (AMOC). While current findings
indicate that these effects occur mostly on year-to-year timescales, under a long-term scenario that includes the
decline in the AMOC circulation (as suggested by !PCC 2013), it is likely that amplified sea level rise rates may be
observed along Southeast Florida through similar mechanisms.
Sea level fingerprinting (Gravitational Effects)
Melting ice sheets in polar regions is one of the main processes contributing to sea level rise, but not in a
spatially uniform manner, because of gravitational forces. Melting ice sheets reduces the mass of water stored
in polar regions and, consequently, reduce the gravitational attraction of continental ice sheets. As a result,
the volume of ocean water near the melting ice sheet decreases, leading to reduction in sea level height near
the polar regions, and an increase in sea level further away. This process is termed sea level fingerprinting
(Mitrovica et al., 2011, 2009). It suggests a counterintuitive change in regional patterns of sea level changes, in
which sea level height decreases near the source of fresh water supply to the ocean.
A sea level fingerprinting study by Hay et al. (2014) suggest that melting of the Greenland Ice Sheet results
in a slightly lower rate of sea level rise along the Florida shorelines with respect to the global mean rate. The
calculated change is 20% of the total contribution of the Greenland Ice Sheet to the global mean rate, which is
currently estimated as 1-1.5 millimeters/year. According to Hay et al. (2014), melting of the West Antarctic Ice
Sheet increases the rate of sea level rise along the Florida coast by 20% with respect to the total contribution of
the West Antarctic Ice Sheet to the global mean rate, which is so far about 0.75-1 millimeters/year. Thus far, the
contribution of sea level fingerprinting in southeast Florida had been fairly small, about 0.2-0.3 millimeters/year.
Unified Sea Level Rise Projection: 2019 Update 28
However, in the future with increasing rate of polar ice melt, the effect of sea level fingerprinting can increase,
especially if the Antarctic Ice Sheet will melt significantly faster than the Greenland Ice Sheet. It should be noted
that the NOAA (2017) scenarios used for the current projections explicitly account for regional fingerprinting.
EFFECTS OF GREENHOUSE GAS EMISSIONS
The Intergovernmental Panel on Climate Change based the climate projections of their Fifth Assessment Report
on four greenhouse gas concentration scenarios, known as the Representative Concentration Pathways (RCPs)
(0PCC, 2014). These RCPs are sets of scenarios for greenhouse gas emission, greenhouse gas concentration, and
land use trajectories; their primary product is greenhouse gas concentration scenarios for use as inputs into
climate models (van Vuuren et al., 2011a). The number in the name of each RCP is the end-of-century radiative
forcing in W/m? caused by the greenhouse gas concentrations in 21 OO.
The lowest concentration scenario, RCP 2.6, is viewed as the scenario necessary to keep global temperature
increases below 2ºC (van Vuuren et al 2011a). This scenario would require that greenhouse gas emissions peak
around 2020 and decrease at 4% annually (van Vuuren et al. 2011a). The highest concentration scenario, RCP
8.5, assumes a greatly increased population with low economic and efficiency gains by 2100, along with a strong
dependence on fossil fuels, including a ten-fold increase in coal use by the end of the century (Ria hi et al., 2011 ).
RCP 4.5 and RCP 6.0 are concentration scenarios sitting between these two extremes. In the RCP 4.5 scenario,
emissions valuation policies, reaching $85 per ton of carbon dioxide by 2100, drive alternatives in energy
production and land use changes to reduce emissions. lt assumes use of bioenergy production coupled with
carbon capture and storage to produce energy with net-negative carbon emissions. RCP 6.0 assumes cost-
effective reduction of emissions through a global emissions permit market, and includes a shift from coal-fired
to gas-fired energy production and more than 30% non-fossil fuel energy production by 2100 (Masui et al.,
2011).
Beyond these four concentration pathways, the IPCC recently released a report outlining the emissions
scenarios required to limit global warming to 1.5°C(0PCC, 2018). In this model pathway, global net
anthropogenic carbon dioxide emissions decline by about 45% from 201 O levels by 2030, reaching net zero
around 2050. The report also contains an emissions projection to limit global warming to 2.0ºC; in this scenario,
carbon dioxide emissions decline by about 25% by 2030, and reach net zero around 2070.
Prior to 2050, different emission scenarios produce minor differences in sea level rise projections, however,
they diverge significantly past mid century. After 2050, the sea level rise projections increasingly depend
on the trajectory of greenhouse gas emissions, underscoring the critical need for urgent and ambitious
decarbonization policies and efforts.
Unified Sea Level Rise Projection: 2019 Update 29
CONSEQUENCES OF SEA LEVEL RISE
Seasonal Cycle of Sea Level and lnterannual Variability
There is a strong seasonality to average sea level variation with any given year. This is primarily driven by
seasonal oceanographic and atmospheric processes such as fluctuations in coastal ocean temperature, salinity,
winds, atmospheric pressure, and ocean currents. In Southeast Florida, the sea level driven by astronomical
tides exhibits a strong seasonality with higher than average values during the months of September to
November with a peak during the month of October (Figure A-4). The seasonal high in October may be as much
as 5-6 inches above the average. The high values during September to November, superimposed on the mean
sea level curve and diurnal and semidiurna! tides further exacerbates the recurrent flooding that has been
increasing in recent years.
In addition to the seasonal fluctuations, sea level may also exhibit interannual variability due to fluctuations
in oceanographic and atmospheric processes (Figure A-4). Such fluctuations may further increase the mean
annual sea level above the average seasonal cycle shown in Figure A-4 and they may persist at a higher or
lower level for several years. For example, Figure A-5 shows that the annual fluctuation since about 2012
has been largely positive until 2019, a pattern that is not characteristic of annual variability since 1990. It is
possible that such a persistence may be due to a systematic trend in ocean currents and/or other atmospheric-
oceanographic process but it is too early to make such an attribution.
Average Seasonal Cycle
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JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
■Lake Worth Pier ■Miami Beach ■Virginia Key Vaca Key ■Key West
FIGURE A-4: Tidal water elevations in the Southeast Florida area average 5 to 6 inches higher at the
end of the summer (NOAA, 2020b). This increases the risk of recurrent high tide street flooding and more
severe storm surge impacts, particularly during periods of astronomical high tides (i.e. king tides). Ongoing and
accelerating local sea level rise will just make this problem worse.
Unified Sea Level Rise Projection: 2019 Update 30
8724580 Key West, Florida
0.30
Monthly mean sea level with the
avenaqe seasonal yde and
linear trend removed
Five-month average
0.15 - - - - - - - - - - - - - - - - - - - - - T - - - - - - - - - - - - - - - - -
0.00 /Pp--4fA.gleam bl Ip I
-0.15 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-L30 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025
FIGURE A-5: The plot shows the interannual variation of monthly mean sea level and the 5-month running
average. The average seasonal cycle and linear sea level trend have been removed (Retrieved from NOAA Tides
and Currents website (https://tidesandurrents.noaa.gov/)
Increase in Recurrent Tidal Flooding
Accelerating rates of sea level rise, due to both global and regional processes, have resulted in increased
flooding frequency in several coastal communities along the US Atlantic coast, including the Southeast Florida
region (Ezer et al., 2013; Ezer and Atkinson, 2014; Kirshen et al., 2008; Kleinosky et al., 2006; Sweet et al., 2018;
Wdowinski et al., 2016; 2019; Valle-Levinson et al., 2017). These recurrent flood events, often termed "nuisance
flooding," occur during high tide conditions, with or without heavy inland rainfall. When flooding events occur
due to high tide flooding alone, they are also termed "king tides", or "sunny-day flooding." Recurrent tidal
flooding results in inundation, impedes access, impairs stormwater drainage infrastructure, and damages
vulnerable systems. With sea level rise, the frequency of tidal flooding will increase, leading to chronic flooding
approaching permanent inundation.
An analysis of flooding frequency from 1998 to 2013 in Miami Beach revealed that recurrent tidal flooding
events quadrupled, from two events during the eight years from 1998-2005, to 8 to 16 total events in the
following eight years from 2006-2013 (Wdowinski et al., 2016). In 2005, 2015, 2016, and 2017, compound
flooding induced by hurricanes led to the highest observed numbers of annual flood days on record (Ezer
and Atkinson, 2017; Ezer et al., 2017; Wdowinski, 2019). From 2006 to 2012, recurrent tidal flooding occurred
approximately every other year, typically during the fall (September through November). Since 2010, higher
than normal tides have also been observed in the winter and spring seasons (Figure A-6, Wdowinski et al.,
2019). In 2019, unprecedented flooding occurred in Key Largo, where a neighborhood was flooded continuously
for more than four months.
How will flooding frequency evolve over time?
On the national scale, NOAA (2014) published an assessment of nuisance flooding finding that the duration
and frequency of these events are intensifying around the United States. Subsequently, Park and Sweet (2015)
demonstrated that coastal areas are experiencing an increased frequency of flood events (an acceleration) over
the last few decades, and that this acceleration in flood occurrence will continue regardless of the specific rate
of sea level rise. The recent assessment published by NOAA (Sweet et al., 2018) in fact shows that the number of
high-tide flooding days has been increasing at a nonlinear rate for locations along the U.S. East Coast, including
Southeast Florida. Results from this assessment indicate that under the NOAA Intermediate scenario, Miami
Unified Sea Level Rise Projection: 2019 Update 31
will likely experience approximately 60 days of high-tide flooding per year by 2050, while under the NOAA
Intermediate-High scenario this number may exceed 150 days per year (Figure A-7, personal communication,
Sweet et al., 2018).
60
50
40
30
20
10
4
-10
-20
-30
4
5
15
14
39
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
FIGURE A-6. Frequency of tidal flooding in Miami Beach, based on Virginia Key tide gauge. Higher than normal
tides shown as red bars in figure. Number of events in a given year listed in right margin of graphic (Wdowinski,
2019).
Unified Sea Level Rise Projection: 2019 Update 32
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300 NOAA interred.ate
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Average Annual Rate of High Tide Flooding per Decade at Virginia Key
90
60
30
o 1980
360
330
300
270 - 240 "' D >- 210
à 180
@ 150 >, "' o 120
90
60
30
o 1980
1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Average Annual Rate of High Tide Flooding per Decade at Key West
t oe
-l l J
1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
FIGURE A-7: Projected annual frequencies of high tide flooding associated with the NOAA sea level rise (Sweet
et al., 2017) estimated at NOAA tide gauges in Virginia Key and Key West. High tide flooding threshold values
levels above MHHW are 0.52 meters for Virginia Key, and 0.53 meter for Key West (Courtesy of William Sweet -
NOAA National Ocean Service).
Groundwater Rise and Reduced Drainage Capacity
Sea level rise may also affect flooding by raising the water table and reducing the ability of rainfall to infiltrate
and be stored in the soil. In coastal areas of Southeast Florida, groundwater levels were observed to rise
at the same rate as sea level rise over the long term (Decker et al., 2019; Sukop et al., 2018). Flooding as a
consequence of groundwater rise and reduced soil storage is anticipated to double or triple in flood frequency
over the next 40 years (Sukop et al., 2018; Obeysekera et al., 2019). By 2070, certain coastal areas of South
Florida are projected to lose all wet season storage capacity (Obeysekera et al., 2019).
In one example, Sukop et al. (2018) examined the long-term record of water levels in a well (G-852, in the North
Miami/Arch Creek area) approximately one mile from tide water at Biscayne Bay. The water levels in the well
have been increasing at approximately 2.8 millimeters/year since at least 1974. This rate is consistent with the
rate of sea level rise at Key West of 2.42 millimeters/year over the same time period. (https://tidesandcurrents,
noaa.go/sltrends/sltrends_station.shtml?id=8724580).
As part of an assessment for the Florida Building Commission, Obeysekera et al. (2019) used projections of sea
level rise from previous versions of this report in groundwater models to estimate the change in water table
elevation in Miami-Dade County by 2069. Between 201 O and 2069, drainage capacity is estimated to decrease
by four to ten inches of water in most of the county (Figure A-8) under the high sea level rise scenario.
Unified Sea Level Rise Projection: 2019 Update 33
FIGURE A-8: Miami-Dade County depth to water in 2069 (left) and loss of wet season soil storage capacity from
2015 through 2069 (right) (Obeysekera et al., 2019).
Increasing sea levels also have the potential to compromise the capacity of coastal water control structures
(also known as salinity barriers). As the ocean-side water levels increase, the water control gates of these
gravity structures cannot be opened due to the threat of saltwater entering into the canals they serve and
potentially contributing to saltwater intrusion (Obeysekera et al. 2011).
Storm Surge, Waves, and Sea Level Rise
Storm surge and sea level rise are independent coastal processes that, when occurring simultaneously, lead to
compounded impacts. Sea level rise has the potential to increase the inland areal extent inundated by surges,
the depth of flooding, power of the surge, and the extent and intensity of damage associated with storm
surge and waves. As a result, severe storms of the future may cause significantly more damage than storms of
equal intensity occurring at today's sea level. The frequency of extreme sea levels that cause severe flooding
will also increase as a consequence of sea level rise (Rasmussen, 2018). To avoid impacts from surge, coastal
infrastructure design elevations and reinforcement will need to consider the relationship between future sea
level rise and surge.
The effects of sea level rise on storm tides or surge is nonlinear and location specific. Analyses that
superimpose sea level rise projections on top of surge depths are likely not capturing the nonlinearity of the
processes, and may possibly underestimate depths and forces. Reduction of sea bottom stress and tidal wave
energy dissipation in waters deepened by sea level rise can result in higher surge heights in shallow nearshore
waters (Arns et al., 2015). Similarly, changes in deep water wave heights and wave periods can increase wave
setup and swash zone activity (Mel et et al., 2018). Location- specific projections of future waves and the
interactions between sea level, tides and surges are not yet available (Oppenheimer et al., 2019), but site-
specific modeling of the impacts of future severe storms on infrastructure has occurred for projects across the
Compact four-county region by increasing water levels to represent future conditions.
Unified Sea Level Rise Projection: 2019 Update 34
Rare, extreme water levels that typically occured once every 100 years in the past are projected to
occur annually or more frequently by 2065 in response to sea level rise (Oppenheimer et al., 2019). The
Intergovernmental Panel on Climate Change has concluded high confidence in this projected frequency and
suggested adaptation planning occur before extreme events become regular in the latter half of the 21st
century. Moreover, the duration, precipitation, landfalls, and intensity of future hurricanes is predicted to
increase with global warming (IPCC, 2014; Knutson et al., 2015; Scocci marro et al., 2017; Yamada et al., 2017).
Natural Resource Degradation
As sea level rise increasingly inundates coastal areas, natural resources in the ecologically diverse and
important transition zone-including mangrove forests, tidal flats, and beaches-will be degraded unless
focused effort is devoted to: 1) accommodating the inland migration of coastal habitats, and 2) implementing
coastal management practices that maintain coastal elevation at pace with sea level rise rates (Glick 2006,
Florida Oceans and Coastal Council 2010). In Southeast Florida, existing urban development in the form of
seawalls, roads, and other infrastructure currently blocks much of the ability of coastal habitats to migrate
as sea level rises. Reduced freshwater delivery and conversion of coastal areas to non-vegetated lands limit
or eliminate plant growth, diminish the capacity for coastal areas to maintain natural system functions, and
result in natural system decline. Intrusion of saltwater inland, into inland water bodies, and within the aquifer
is already negatively impacting freshwater resources. With further sea level rise, these impacts will worsen or
accelerate without adaptation that includes coastal management. Inundation of shorelines will also increase
the extent and severity of beach erosion in previously stable coastal areas. In combination, these impacts will
cascade throughout the region's ecosystems even if they are not immediately adjacent to open water areas.
These ecosystems (natural infrastructure) and the natural resources they support, are critical to the resilience
of people and the urban environment. Natural systems provide many important benefits. These include
providing nesting, spawning, and feeding habitat for numerous species including sea turtles, shorebirds,
fish, and invertebrates; contributing to climate change mitigation via sequestration of carbon dioxide from
the atmosphere; enhancing storm protection, water and air purification; moderating urban heat effects; and
supporting livelihoods and economic activity throughout South Florida that depend on tourism and recreational
and commercial fisheries. The region can manage for natural resource benefits by providing space for habitat
transitions, implementing practices that help adapt coastlines to sea level rise, and reducing anthropogenic
pressures (e.g., nutrient and solid waste pollution, recreational activities that can damage natural resources,
development practices) that would compound the degrading effects of sea level rise.
Unified Sea Level Rise Projection: 2019 Update 35
SOUTHEAST FLORIDA
1 REGIONAL COMPACT
CLIMATE
CHANGE
For more information, visit:
www.climatecompact.org