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Case Studies of Analyzing Vulnerability for Post‐
Disaster Redevelopment Planning
INTRODUCTION
This section includes methodologies and case studies to assist communities with the development of a PDRP
vulnerability assessment. The vulnerability assessment is conducted to determine areas that are vulnerable to
natural (and/or human induced) hazards that will most likely be damaged and need to be redeveloped after a
disaster. First, the community identifies hazards that could cause damages significant enough to warrant
redevelopment to provide focus for assessment. Then, the vulnerability assessment examines the hazards
vulnerability of and potential impacts to people, property, infrastructure, the economy and areas throughout
the community.
PURPOSE
The community stakeholders use the vulnerability assessment, other local knowledge and existing programmatic
and procedural capacity to develop the PDRP Action Plan to address post‐disaster redevelopment issues. The
vulnerability assessment can be used to target which structures and infrastructure should be restored back to
pre‐disaster condition or which ones should be modified through construction practices, siting or design practice
to reduce future hazard impacts.
EXPANDING ON EXISTING VULNERABILITY ASSESSMENTS
Similar to the Local Mitigation Strategy (LMS), the PDRP vulnerability assessment affords the community a
quantifiable and spatial understanding of their risk so they can implement pre‐ and post‐disaster hazard
vulnerability reduction measures. Yet, the PDRP vulnerability assessment delves deeper into some areas of
vulnerability, not required for the LMS, such as the local economy and the natural environment.
There is no need to “recreate the wheel” if the LMS vulnerability assessment is current. The PDRP vulnerability
assessment can simply build on the one created for the LMS, as similar stakeholders often contribute to the
development of both of these vulnerability assessments and the information should be consistent for planning
purposes. In addition to vulnerability assessment elements that were included in the Florida PDRP pilot project
communities; other topics may be included to enhance the analyses.
The LMS and PDRP vulnerability assessment elements are compared in Table 1. The LMS requirements are
based on the Federal Emergency Management Agency Local Mitigation Plan Crosswalk, per the Disaster
Mitigation Act of 2000. LMS elements that are recommended, not required, are highlighted in gray.
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Table 1. Comparison of Vulnerability Assessment Elements
Elements LMS PDRP
Description of all natural hazards that affect the jurisdiction; hazards, for which a major or catastrophic event could result in redevelopment efforts for PDRP. √ √
Identification of geographic areas affected by each natural hazard; hazards, for which a major or catastrophic event could result in redevelopment efforts for PDRP. √ √
Identification of the extent (magnitude/severity) of each hazard; hazards that could result in redevelopment efforts for PDRP. √ √
Provision of previous occurrences (hazards history) and probability of future events. √ √
Summary description of each jurisdiction’s vulnerability to each hazard; hazards that could result in redevelopment efforts for PDRP. √ √
Description of impacts of each hazard on each jurisdiction; hazards that could result in redevelopment efforts for PDRP... √ √
Identification of the types and numbers of repetitive loss properties. √ √
Vulnerability, in terms of the types and numbers of existing buildings, infrastructure and critical facilities located in hazards areas. √ √
Vulnerability, in terms of the types and numbers of future buildings, infrastructure and critical facilities located in hazards areas. √ √
Estimation of potential dollar losses to existing and future vulnerable structures, and description of methodology. √ √
Description of land uses and development trends. √ √
Types, numbers and locations of people (e.g., general, special needs, etc.) who could be impacted by hazards that could result in redevelopment efforts.
√
Locations of sites used for/to support post‐disaster operations (e.g., debris reduction, recycling and staging; landfills; logistical staging; faith based organizations).
√
Analysis and geographic location of the age of construction and building codes and regulations in hazard areas that may require redevelopment.
√
Future land use maps with hazard layers to show hazard vulnerable areas of future development. √
Identification of areas suitable for temporary housing and affordable housing. √
Economic analysis of economic centers, major employers and small businesses, to include site identification in hazard vulnerable areas.
√
Location of environmentally sensitive and natural areas with hazard layers. √
Location of public and private water/wastewater utilities and storm water management systems in hazard areas and environmentally sensitive areas.
√
Location of historical and cultural resources in hazard vulnerable areas. √
Location of critical priority redevelopment areas. √
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VULNERABILITY ASSESSMENT METHODOLOGIES, BEST PRACTICES AND
INDICATORS
There are a number of existing methodologies, best practices and indicators that have been used for the LMS
and PDRP pilot project vulnerability assessments. These methodologies and best practices are described in this
section, followed a by case study examples methodology and best practices used for communities that
participated in the Florida PDRP pilot project in the following section. Various vulnerability assessment
methodologies are often used based on local capacity: staff, software, data availability, time and money.
A community’s vulnerability can be examined using the indicators listed in Table 2, as they relate to the PDRP
Guidebook topics.
Table 2. Comparison of Vulnerability Assessment Criteria and PDRP Guidebook Topics
Vulnerability Assessment Indicators
PDRP Guidebook Topics
Land Use Housing Economy Infrastructure Health & Social Services
Environment
Physical √ √ √ √
Social √ √ √
Economic √ √ √
Environmental √ √ √ √ √ √ Land Use √ √ √ √ √ Operational √ √ √
Vulnerability Assessment Methodologies and Best Practices
A variety of existing vulnerability assessment methodologies and tools are available. Some of these resources
are described in more detail below.
FDEM Hazard Analysis Toolkit
The Florida Division of Emergency Management (FDEM) has prepared a list of vulnerability assessment
methodologies and Websites that can be used to obtain hazards data and information to assist local
governments.
For more information, please visit:
http://www.floridadisaster.org/Mitigation/Local/Documents/Hazard%20Toolbox.pdf
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FEMA How‐to‐Guides
The FEMA Mitigation Planning #2 How‐to‐Guide entitled, Understanding Your Risks: Identifying Hazards and
Estimating Losses (FEMA 386‐2) provides step‐by‐step guidance on how to perform a risk assessment.
For more information, please visit: http://www.fema.gov/library/viewRecord.do?id=1880
HAZUS‐MH
Hazards United States‐Multi‐Hazards (HAZUS‐MH) is FEMA’s standardized loss
estimation methodology built upon an integrated GIS platform to conduct analyses at a
regional level for coastal and inland flood, hurricane wind and earthquake hazards.
HAZUS‐MH uses physical vulnerability characteristics as the basis for generating
potential loss estimates for physical damage (structures and infrastructure), economic
loss (lost jobs, business interruptions, repair and reconstruction costs), social impacts
(displaced households, shelter estimates, population exposed to hazards) and debris
estimates. HAZUS‐MH includes US Census (2000), Dun & Bradstreet and R.S. Means (2006) data to establish
building counts and valuation. HAZUS‐MH default data can be updated with more current local data to increase
the validity and accuracy of the results.
HAZUS‐MH was used in pilot project PDRPs for Manatee, Nassau and Polk counties.
For more information, or to request a free copy of HAZUS‐MH, please visit:
http://www.fema.gov/plan/prevent/hazus/index.shtm
MEMPHIS / TAOS
The Florida Division of Emergency Management’s (FDEM) Mapping for Emergency Management Parallel Hazard
Information System (MEMPHIS) provides mapped and tabular vulnerability and loss estimates for various
hazards in Florida, such as hurricane, tornado, thunderstorm and hail damage, earthquake, and potential for
wildland fires, tsunamis, and sinkholes. MEMPHIS uses The Arbiter of Storms (TAOS), which identifies areas
within each county that are vulnerable to damage from high winds, storm surge and inland flooding along with
estimates of damage. MEMPHIS was developed in support of Florida’s statewide LMS project.
For more information, please visit: http://lmsmaps.kinanco.com/
GIS Analysis
GIS analyses may be performed using local data to augment the afore mentioned methodologies to further
understand vulnerability. Hazards layers, which are not currently included in the methodologies described
above or more current data (e.g., flood, surge or sea level rise), can be assessed. For example, the GIS analysis
can incorporate Digital Flood Insurance Rate Map (DFIRM); Sea, Lake and Overland Surges from Hurricanes
(SLOSH) and the Southern Wildfire Risk Assessment data. Analyses may consist of overlaying hazard layers the
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following data sets: parcels, local businesses and economic centers, critical facilities, historic and cultural sites,
environmentally sensitive areas, conservation areas, structures/sites that have been mitigated or identified to
be mitigated, existing and future land‐use, debris sites, public and private water and wastewater facilities and
service areas (e.g. public v. wells or septic), areas suitable for temporary and affordable housing,
REMI
REMI’s Policy Insight® is a structural economic forecasting and policy analysis model. REMI integrates input‐
output, computable general equilibrium, econometric and economic geography methodologies. The model
provides dynamic forecasts and simulations generated on an annual basis and behavioral responses to wage,
price and other economic factors. The model identifies economic outputs; labor and capital demand;
population and labor supply; wages, prices and costs and market shares.
For more information, please visit: http://www.remi.com/
Vulnerability Assessment Indicators
Physical Vulnerability
Physical vulnerability assesses the types, number and value of structures (e.g., residential, commercial,
industrial, governmental, historic, cultural, essential and critical facilities) and infrastructure (e.g., roads, bridges,
ports, airports, utilities, communications, etc.) in a community to quantify hazards exposure, and disaster
damage and loss.
The LMS vulnerability assessment is required to include the number and types of structures, infrastructure and
critical facilities that are vulnerable (exposure) to various hazards. Where possible, loss estimates for each
hazard are encouraged to be calculated as well. However, additional analyses should be included in the PDRP
vulnerability assessment, such as:
Expected building damage by occupancy class
Mobile home vulnerability
Permanent versus seasonal home vulnerability
Historic and cultural site vulnerability
Faith‐based organization facility vulnerability
Building Codes in effect and wind design loads based on age of structures
National Flood Insurance Program participation commencement and age of structures
Non‐conforming structures
Social Vulnerability
Social vulnerability assesses the demographic characteristics of a community to gauge who could be impacted
by a disaster, and the types and quantities of pre‐and post‐disaster assistance needed by the population.
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Social vulnerability can include characteristics of1:
special needs (infirmed or transient)
age (65 years and older and under five)
socioeconomic status (at or below poverty level)
race and ethnicity (cultural and language barriers that affect access to disaster recovery information and
assistance)
gender (women often are limited to gender‐specific employment, lower wages and assume care‐giving
roles)
household status (headed by a single parent)
education level
homeownership versus renting
population growth and density
health status and availability of health care services.
The Social Vulnerability Index of the United States (SoVI) 2
provides a socioeconomic and demographic profile of the US.
Featuring US Census data (1960‐2000), in a GIS platform, SoVI
uses a consistent set of measures to assess social vulnerability
at the census block level to show communities’ disaster
preparedness, response and recovery capacities. The variables
of the methodology are based on literature and post‐event field
studies conducted over the past 50 years. The socioeconomic
and built environment data were compiled and georeferenced
at the University of South Carolina’s Hazards Research Lab.
There are future plans to incorporate SoVI type measures into
HAZUS‐MH to integrate social and physical vulnerability.
The LMS is required to contain a description of the jurisdiction’s
vulnerability to hazards and potential hazard impacts. This is
mainly geared toward physical structures and infrastructure, as
the LMS is used to identify and prioritize hazard vulnerability
reduction (mitigation) measures. Although the LMS
vulnerability assessment is not required to include social
vulnerability indicators, such data is often included.
For more information on SoVI, please visit: http://webra.cas.sc.edu/hvri/products/sovi.aspx
1 Heinz Center, 2002. Human Links to Coastal Disasters. Washington D. C.: The H. John Heinz III Center for Science, Economics and the Environment. 2 Cutter, S.L., B.J. Boruff, and W.L. Shirley. 2003. “Social Vulnerability to Environmental Hazards.”Social Science Quarterly84(1): 242‐261.
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Economic Vulnerability
Economic vulnerability analyzes the local economy in terms of how the following indicators could be impacted
by a disaster, such as:
employment by industry
unemployment rate
income levels
business physical structure and operational vulnerability
workforce housing and infrastructure requirements for business resumption
future land use for commercial and industrial purposes
the community’s long‐term economic development vision
Data, information and analyses may be available from local jurisdictions, Enterprise Florida, regional economic
development organizations, chambers of commerce or local colleges or universities, and are often conducted by
businesses themselves. It can be helpful to ascertain whether large and small businesses have business recovery
and/or continuity of operations plans.
The LMS is required to assess vulnerability and, where possible, loss estimates for the number and type (e.g.,
commercial and industrial) of structures; include major employers, financial centers and business or retail
districts, but is not required to include an economic impact analysis.
Environmental Vulnerability
Environmental vulnerability analyzes the potential impacts of hazards to the natural environment, public health
and safety, recreation and tourism and quality of life. This can be done by examining environmentally sensitive
areas (wetlands, endangered or threatened species habitat), waterways, open space, aquifer recharge areas,
underground springs, the Coastal Barrier Resource System, marine fisheries and conservation areas. Impacts
may be assessed to the natural environment itself, and the secondary impacts that are caused if the natural
environment is degraded.
The LMS is required to address impacts to natural resource areas. The LMS vulnerability assessment may not go
into the depth that might be desired for the PDRPP, such as the extent of how damaged or polluted natural
environments (e.g., water bodies or marshland) will impact the natural areas themselves, recovery capabilities
(e.g., debris removal and disposal) and the local economy (e.g., recreation and tourism).
Land Use Vulnerability
Land use vulnerability assessments can be used to identify the acreage by land use classification in hazard areas.
This can include the identification of existing land use and future land use. It is useful to quantify the vacant
acreage and non‐conforming land uses. It is important to assess how and where the community will redevelop,
based on existing and future land use and zoning requirements, to reduce future hazards vulnerability.
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The land use analysis can assist local policy staff determine whether modifications should be made to existing
land development codes, zoning, ordinances and procedures. It also provides a mechanism to hold charettes
with local stakeholders to identify potential redevelopment scenarios for a major or catastrophic disaster.
The LMS is required to provide a general overview of land uses and types of anticipated future development.
The analysis should differentiate land uses of similar types that have different densities. The LMS vulnerability
assessment may not provide as much detail needed for the PDRP, as described previously.
Operational Vulnerability
Operational vulnerability assesses government, private sector and hospital functions, as well as how the location
of short‐term disaster recovery sites can impact long‐term recovery and redevelopment. Sites to examine can
include debris sites (staging, reduction and recycling; landfills by type), temporary housing sites (group and on‐
site with primary residences or businesses, and faith‐based organization facilities (provide assistance to the local
community). It can be helpful to identify whether the local government has a Continuity of Government plan, as
well as Continuity of Operations Plans for key departments.
The LMS is required to assess functional impacts to critical facilities and economic elements. The LMS
vulnerability assessment could be expanded on if additional information is needed for the PDRP, as described
above.
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CASE STUDIES
Various vulnerability assessment indicators are exemplified through case studies from the Florida PDRP pilot
project for Manatee, Nassau, Polk and Sarasota counties.
Manatee County
Physical Vulnerability – Mobile Home GIS Analysis
Manatee County performed a GIS analysis to identify the number of mobile homes that are vulnerable to natural
hazards. Storm surge and flood hazard areas overlaid with a mobile home building footprint layer. Table X
provides an overview of the number of mobile homes, by jurisdiction that is at risk to storm surge and flooding.
There are no mobile homes in Anna Maria, Holmes Beach or Longboat Key.
Table X. Mobile Homes Located in Known Flood Hazard Zones
Jurisdiction
Total
Number
of Mobile
Homes
Number of Mobile Homes in Hazard Zones
25
year
floodplain
1
Percent
Annual
Chance
0.2
Percent
Annual
Chance
Coastal
VE
Zone
Category
1
Storm
Surge
Category
2
Storm
Surge
Category
3
Storm
Surge
Category
4
Storm
Surge
Category
5
Storm
Surge
Unincorporated
Manatee County 27,096 232 7,707 2,711 193 2,588 4,583 6,314 8,722 12,459
Bradenton 1,455 NA 901 87 0 221 413 417 514 868
Bradenton
Beach 283 NA 283 0 0 160 305 305 305 305
Palmetto 2,121 NA 1253 428 0 307 1,319 1,542 2,226 2,255
Nassau County
Physical Vulnerability – Damaged Property
A deterministic HAZUS‐MH scenario was run for the October 2, 1898, a Category 4 hurricane that made landfall in Camden County, Georgia, with sustained winds of 135 miles per hour (mph). This hurricane caused 53 casualties and $2.5 million (1898 dollars) in losses in Nassau County over a century ago. Loss estimates for current building stock were modeled using parameters for the 1898 Hurricane (i.e., storm track, forward speed, radius to maximum winds, and barometric pressure). The hurricane parameters were derived from ongoing research by Warning Coordination Meteorologist of the NOAA National Weather Service in Jacksonville, Florida.3
3 University of Florida and Nassau County Emergency Management Nassau County, Florida Hurricane Simulation and Damage Assessment. January 21, 2007.
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Previously, the University of Florida and Nassau County Emergency Management jointly conducted a HAZUS‐MH analysis using MR2. This assessment is an updated analysis using MR3. Although the hurricane made a direct landfall 12 miles north of the Nassau County border, the county still experienced significant damage.
Table X summarizes the expected building damage by occupancy if the 1898 Hurricane were to occur today. HAZUS‐MH estimated that about 19,515 or 80 percent of the county’s buildings would be at least moderately damaged and 6,821 buildings would be completely destroyed.
Table X. Expected Building Damage by Occupancy Class by Hurricane Wind Occupancy Class Minor % Moderate % Severe % Destroyed % Total
Agriculture 1 12.18% 2 21.54% 4 40.78% 1 16.32% 8
Commercial 21 6.54% 59 18.25% 197 60.58% 25 7.65% 302
Education 0 7.71% 1 16.96% 4 64.27% 0 2.32% 5
Government 1 7.09% 4 17.62% 14 65.98% 0 1.24% 19
Industrial 3 6.33% 8 14.93% 33 63.77% 4 7.59% 48
Religion 4 10.13% 8 21.30% 22 55.45% 2 4.20% 36
Residential 2,718 11.40% 5,421 22.73% 6,919 29.01% 6,788 28.47% 21,846
TOTAL 2,748 5,503 7,193 6,820 22,264
Source: HAZUS‐MH MR3
There are an estimated 3,146 or 27 percent of the masonry buildings and 2,522 or 37 percent of the manufactured homes that would be completely destroyed.
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Physical Vulnerability – Historic Properties
A GIS analysis was conducted to identify the historic properties that are located in the 100‐ and 500‐year floodplain; 1% and .02% annual chance flood (ACF). Historic properties were included that were listed on the National Register of Historic Places (NRHP) maintained by the Secretary of the Interior or by the State Historic Preservation Office (SHPO) as being historically significant. For the purposes of this study, historic properties consisted primarily of buildings (based on building footprint data) and their related parcels.
According to the National Register Information System4 and data provided by the SHPO, there were 10 individual National Register entrees for Nassau County plus two historic districts and the Original Town of Fernandina Historic Site and 894 properties recognized by SHPO that includes NRHP properties and other properties of historic significance dating from c1839 to c1965. Figure x illustrate the intersection of 197 historic buildings with the boundaries of the 1% ACF hazard and the 0.2% ACF hazard.
Figure x. Nassau County Historic Property Exposure to Flood Hazards
4 The National Register Information System (NRIS) is a computerized database accessible via the National Park Service Web site (www.nps.gov) that contains information on every property in the National Register of Historic Places.
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Economic Vulnerability – Agriculture
Nassau County has a diverse economy, ranging from agricultural and sylvicultural activity in the west and central areas (predominantly tree farms), to a variety of economic sectors in the eastern portion of county such as commercial, industrial, manufacturing and tourism. Rayonier, a major employer in the area, owns most of the land used for tree farming and a large pulp mill in Fernandina Beach. Historically, tree farming, trucking and paper production has accounted for a large part of the economy. However, that is changing due to growth in the county. Figure x shows the agricultural lands, including tree farming, which are potentially vulnerable to flood and wildfire hazard.
Figure x. Nassau County Agricultural Lands in Flood, Surge Susceptible and Wildfire Areas
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Polk County
Physical – Housing Stock Wind Vulnerability
Vulnerability to wind
Typically, the current stock of affordable housing consists largely of mobile homes, older and less substantially
constructed homes, and rental properties. These structures are more likely than most housing to suffer
damage, or otherwise declared uninhabitable. Only since the recent advent of disasters like Hurricane Andrew
have more stringent building codes been implemented, even for lower income housing. These losses can have
an exacerbated impact on current affordable housing problems. Without affordable replacement housing for
residents and commercial buildings for businesses, full repopulation will be problematic. And without the ability
to maximize repopulation, there may not be sufficiently large and diverse business, worker and consumer bases
upon which to effectively rebuild the local economy and reestablish the standard of living to which we have
become accustomed.
Knowing that older homes may be one of the variables that increase their vulnerability to wind, the year a
structure was built is an important element in determining risk from wind damage. Vulnerability to wind
damage is categorized into 3 main groups:
Least vulnerable: Structures built 2002 to present
More vulnerable: Structures built from 1994 to 2001
Most vulnerable: Structures built prior to 1994
Using this classification system, the following pivot tables provide two perspectives regarding the breakdown of
wind vulnerable housing stock. Pivot Table 1 is an analysis of the percentage of structures based on the year a
structure was built. Pivot Table 2 is an analysis of the percentage of structures based on residential or
non‐residential usage type.
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Pivot Table 1: Count & Percentages by Year Built
Year Built Residential5 Non‐Residential Total by year built
Built prior to 1994 137,169
(91.02%)
13,523
(8.97%)
150,692
(100%)
Built from 1994 to 2001 30,005
(94.12%)
1,874
(5.88%)
31,879
(100%)
Built 2002 and later 43,669
(96.93%)
1,385
(3.07%)
45,054
(100%)
Total by use type 210,843
(92.63%)
16,782
(7.37%)
227,625
(100%)
Social Vulnerability – Homeownership
Homeownership
Figure 5 illustrates the breakdown of mortgage holders vs. renters.6 The percentage of renters in the
community is important since not owning a home may make this segment of the population more likely to leave
the area after a disaster since they are less “tied” to their domicile.
Figure 5: Mortgage Holders vs. Renters
Almost a quarter of the housing population pays 30% or more of their monthly income for housing. Table 10
breaks down the cost burden of the county’s housing population.
5 Data obtained from the Polk County Property Appraisers office and includes single family, mobile/modular, and multi-family buildings. NOTE: analysis pertains to structures only and not total housing units (i.e. 1 multifamily structure may contain 32 units).
6 U.S. Census Bureau, 2006 American Community Survey
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Table 10: Households by Cost Burden (2005)7
Table 10: Amount of Income Paid for Housing
0-30% 30-50% 50% or more
Owner 123,069 (58.32%) 20,089 (9.52%) 11,580 (5.49%)
Renter 37,740 (17.88%) 9,785 (4.64%) 8,752 (4.15%)
Total 160,809 (76.21%) 29874 (14.16%) 20,332 (9.64%)
Economic – Regional Interdependencies
SRI International’s report emphasizes that “industry clusters do not operate in a vacuum, but instead are closely
interconnected with and influenced by the companies, key institutions, natural resources, and other economic
assets present within the broader Central Florida region.” Their report included Orange, Hillsborough, Hardee,
and Highlands Counties as part of its regional cluster analysis. The detailed analyses for these respective
counties can be found in their assessment.
Earnings Flow
Based on the regional industry cluster analysis, the possibility exists that there is interdependency as it relates to
earnings flows across counties. Three types of earnings flow can exist which can greatly impact the economic
redevelopment of the county. One of the following earnings scenarios can exist: 8
Domestic earnings: Wages which are earned in the county in which the residents live (i.e. wages earned by Polk County residents that are employed within Polk County).
Imported earning: Wages earned from employed populations that work outside of their county of residence and bring their paychecks home (i.e. wages earned by Polk County residents that are employed outside of Polk County).
Exported earnings: People who commute into a county to work and take their earnings back to their county of residence (i.e. wages earned by people from other counties who come to Polk County to work).
The following data in Table 17 was noted from the US Census County to County Worker Flow files9
7 Florida Housing Data Clearinghouse, See http://flhousingdata.shimberg.ufl.edu/a/profiles?action=results&nid=5300#afford_housing_need 8 Sally Sleeper, et al., “Measuring and Understanding Economic Interdependence in Allegheny County,” The RAND Corporation, 2004. 9 2000 US Census, County to County Worker Flow Files. http://www.census.gov/population/www/cen2000/commuting/index.html
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Table 17: Earnings flow for Polk County
Type of Earning Number of People
Domestic Earnings 170,673
Imported Earnings 31,668
Exported Earnings 17,602
Ratios for Understanding Economic Interdependence
Using captured earnings and generated earnings, two metrics of economic interdependence for Polk County can
be calculated. The first metric, the exported earnings ratio, is calculated by dividing the county’s exported
earnings by its generated earnings. This reveals the degree to which the county is a source of income to other
counties. A value of zero would indicate that there are no commuters outside of Polk, while a value of 1.0
would result if a nonresident held every job in Polk County. Higher numbers indicate greater economic
interconnectedness. Using this formula, the exported earnings ratio is .10 (or 10%). (NOTE: Due to the
aggregation of median incomes of other counties, some counties will derive more of its income from Polk
residents than others).
The second metric, the imported earnings ratio, measures how dependent the county is on income from those
who travel outside Polk to work. It is calculated by dividing the imported earnings of the county by its captured
earnings; as with the previous analysis, values closer to 1.0 indicate a greater degree of economic
interdependency. For Polk County, the imported earnings ratio is .15 (or 15%). This means that 15% of the total
earned income flowing into Polk County is generated by jobs located outside the county.
Although these calculations do not currently reflect a high degree of interdependence among earnings flow.
However, one of Polk County’s key strengths is its central location in the state as well as major east‐west and
north‐south transportation arteries. The county provides a hub for access to the largest population base in the
southeastern United States: 8.5 million people reside within a 100‐mile radius. As industry clusters become
more interdependent within the region, it is quite possible these ratios could change. Other key strengths notes
by SRI International’s analysis that could also influence earnings flow interdependence are: post‐secondary
educational institutions, public‐private sector collaboration and partnerships, and the overall business climate
which is viewed as very favorable.
High or low ratios in the interdependence of earnings flow can be have advantages and disadvantages for each ‐
one is not necessarily more preferable than the other. For example, the current situation of a relatively low
ratio could be an advantage if a disaster struck in the region, but left Polk County relatively untouched.
However, if the concentration of the disaster was focused mainly in Polk County, this could have a far more
devastating effect. Determining the ratio of earnings interdependence is simply one of many economic
variables that must be monitored in order to evaluate potentially harmful ramifications.
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Sarasota County
Physical Vulnerability ‐ Sea Level Rise
Over the coming decades it is expected that much of coastal Florida will face increased coastal erosion, flooding of low‐lying areas and more severe storm surge resulting from rising sea levels (Lausche, 2009). Sarasota County is particularly vulnerable to the threat of sea level rise due to the state’s extensive urban development in low‐lying areas and along the coastlines, the economic importance of tourism, its unique ecosystems, and its reliance on groundwater. The PDRP is a useful plan in which to begin considering to the potential impacts of accelerated sea level rise since opportunities for cost‐effective adaption may be present during disaster redevelopment. Predictions on the rate of sea level rise coastal areas will experience over the next several decades are still without 100% certainty. Predictions depend on global factors and local particulars such as the type of shoreline. For example, sandy beaches are likely to erode more quickly than hard, impervious rocky shorelines. What is certain, however, is that there is enough evidence to show that the sea is rising, and will continue to rise for many years. There also is evidence that shorelines are disappearing as a result of this. Both the U.S. Climate Change Science Program and the Florida Oceans and Coastal Council published reports in January 2009 that identified the key expected effects of sea level rise on coastal areas in the United States. Key findings from this report identify the following potential effects from sea level rise: inundation of currently dry land, increased erosion on the barrier islands and sandy shore environments, loss of the nation’s tidal wetlands, movement of more habitats inland, and a threat to coastal ecosystems due to a loss of tidal marshes (Lausche, 2009). Figures 2.10 through Figure 2.13 present potential increased storm surge from three sea level rise scenarios for Sarasota County. The scenarios are based on data from a project that was led by Pennsylvania State University with support from the U.S. Geological Survey and NOAA.
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Table 2.10 shows the potential effect of different levels of storm surge with an associated 30‐, 60‐, or 90‐cm sea level rise. The percent population within storm surge zones increases based on the rise in sea level. For Category 1 and 2 storm surge, there is almost a 4% increase between current storm surge zone and storm surge zone with an associated 30‐cm rise in sea level. A Category 3 storm surge has almost a 12% increase with a 30 cm rise. Table 2.10 Total Population Impacted by Current Storm Surge and Storm Surge Increased by Sea Level Rise
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Economic Vulnerability – Property Tax Analysis
