LMS Part 1 - Vulnerability Assessment

STEP 3

DEFINING HAZARD AREAS

Overview of the mapping process

When the hazards have been identified and their mode of impacting people and property characterized, the Working Group can begin to define the actual vulnerabilities of the community. While there are different approaches to this analysis, a straight forward one begins with mapping the geographic areas impacted by each hazard in order to compare them to the population, property, facilities and environmental resources existing within them. Computerized mapping makes this process easier, and many Working Groups will have access to a geographic information system (GIS), because many local agencies now have GIS software and equipment. The Florida Department of Community Affairs will also be providing GIS-based maps of vulnerable areas to each county. All of these activities are discussed in this section.

Mapping the geographic extent of a hazard

The mapping process begins with estimating the geographic area likely to be affected by the impact(s) that a specific hazard can cause. For several hazards, county or city agencies may already have done this work and may have also entered the information into a GIS program. The Working Group should first determine if local government has already identified geographic areas threatened by specific hazards, If not, there are several resources that would be available to the Working Group for this purpose, depending on the hazard being evaluated. Using these resources, the Working Group could develop hazard area maps for the following:

• Hurricane storm surge zones — Storm tide atlases and definition of coastal evacuation zones
• Flood plains - Flood Insurance Rate Maps, from the Federal Emergency Management Agency
• Flood prone areas - Local knowledge of flood prone areas outside designated flood plains
• Sinkhole areas - Data from the Florida Geological Survey
• Aircraft landing zones - Local airport managers or the Federal Aviation Administration maps
• Hazardous materials impact zones - Various computer modeling techniques for dispersion of toxic or dangerous gases from facilities or transportation corridors
• Coastal or river oil spills - Computer models available from the US Environmental Protection Agency and other sources; Environmental Sensitivity Index maps from the Florida Department of Environmental Protection
• Lightning and tornado strike areas - Information on historic trends may be available from previous research or Internet sources (See page 9)
• Targets for terrorism and civil unrest - Law enforcement agencies, US Department of Justice and Department of Defense
• Areas subject to wildfires - Fire departments historical records and environmental atlases; US Forest Service
• Drought, frost and hail areas - Historical records from the US Weather Service
• High wind areas - The wind model computer program available from the Florida Division of Emergency Management

In addition to these types of hazards, every community may have unique or unusual hazards that need to be considered. Historical records and/or information from local experts and citizens could be used to provide estimates of the zones or locations potentially vulnerable to these types of events.

Further, some GIS programs can directly incorporate predictive hazard analysis models that Working Groups could find useful in completing this step in the preparation of a local mitigation strategy.

Of course, many types of hazards can be predicted to impact the entire jurisdiction or any location within it. For these hazards, such as hurricane winds or tornadoes, etc., the vulnerability of the entire jurisdiction will need to be evaluated in the subsequent planning process.

As it initiates the mapping effort, each Working Group should prioritize its work to ensure that it has adequately addressed the hazards of greatest concern in its initial planning. This will avoid creating a tremendous volume of data that would be difficult to effectively utilize in the subsequent planning.

Advantages of a GIS-based mapping approach

When the geographic boundaries of specific types of hazards and/or their impacting agents have been estimated or defined, they can be illustrated on maps, preferably using a GIS program.

Defining the hazard areas on maps within a GIS program during this step will offer the Working Group several advantages. First, it will make the subsequent planning effort easier and more accurate, for different maps and databases can be readily compared and updated. Secondly, many counties may also have existing databases, such as property appraisal maps, that can be used within a GIS program to support the subsequent planning process. Finally, the use of a GIS program will further provide the Working Group with significantly more flexibility later in the process to analyze different options for mitigation initiatives as they finalize their Local Mitigation Strategy.

Using a GIS program has so many advantages in the development of a Local Mitigation Strategy that, for those counties and cities that do not have this capability, the Working Group should consider using a portion of the funding available from the Department of Community Affairs to contract with an outside organization for GIS services.

Hazard maps available from the Department

As a part of its technical support program to develop a state-wide vulnerability assessment, the Florida Department of Community Affairs will be providing each county with maps illustrating, where applicable, areas subject to storm surge, inland flooding and wind fields. These maps will be produced using the The "The Arbiter of Storms" (TAOS) computer model, which will assess the state*s hurricane records to predict these specific effects in every county. This information is anticipated to be available by September, 1998, and will be provided to counties as 11"x17" and 22"x32" or 34"x44" maps, as well as on a CD-ROM. The information on the compact disk, once it is downloaded onto the computer hard drive, can be read by most commonly used GIS software. These maps will provide an excellent tool for a Working Group to analyze the geographic areas of the county and its municipalities that are vulnerable to the impacts of all types of tropical cyclone hazards.

Defining areas impacted by "lifeline" damage

The process to define the geographic areas that could be affected by a hazard should consider that, disasters that occur in one geographic area can have direct impact in another, due to the failure of a system providing vital services or products to the community. Such system failures can occur as a result of all types of hazards, and are often associated with damage to ‘lifelines’ or the linear components of the infrastructure important for sustaining normal community functioning.

In identifying geographic areas vulnerable to the impacts of lifeline system failure, two factors warrant consideration:

• Often, the vulnerable geographic area coincides with the service area of a particular lifeline system, such as the area served by a municipal water system or a specific electric power substation, and

• Lifeline systems often have specific components that are the most vulnerable to failure during a disaster, and, if damaged, have widespread consequences.

In mapping the geographic areas most vulnerable to the impacts of lifeline system failure, a Working Group may find a four step process helpful:

Step 1: Define the lifeline systems to be addressed in the analysis,

Step 2: Enlist the cooperation of the owners and/or operators of the lifeline systems,

Step 3: Identify critical components in those systems most vulnerable to disaster-caused damage, and

Step 4: Determine the geographic area of the county and cities that would be impacted if such a critical component were to fail.

As an illustration of this process, consider that bridges are often used to carry a variety of utilities across a river, lake or bay. If a disaster causes the bridge to collapse, then the utility lifelines would also be severed.

Many lifeline systems have vulnerable components such as a bridge, pumping station, or terminal, etc., that are located in flood plains, storm surge zones, or other higher risk areas. Very often, there is also no redundant or alternative capability for continuing to provide service in the event that a flood, for example, was to damage or destroy that vulnerable component. Failure of a bridge could not only block traffic over adjoining roadway, but also could cause loss of utilities on one or both sides of the waterway.

In considering system failure at such critical points, it is often possible to identify a specific geographic area that would be impacted, and to predict the safety, health and economic impact that could result within that area. Therefore, the Working Group will also be interested in mapping the geographic areas vulnerable to the impacts of such a lifeline system failure.

It is possible that the owner or operator of a critical lifeline system, such as the electric power utility, has already conducted an analysis of the vulnerability of their system, as well of the consequences of a failure of its critical components. The results of the analysis may have already been mapped using a GIS program as well. The Working Group should be sure to involve representatives of the lifeline systems in order to benefit from the expertise they could contribute, to fully understanding the geographic extent of the community*s vulnerability to system failure.

- - BACK - -    - - NEXT - -