Chapter 7 Risk and Vulnerability Analysis

Transcription

1 Chapter 7 Risk and Vulnerability Analysis Hazard Ranking Methodology After a thorough review of the community profile, a county hazard ranking was completed using a three-step process. The first step was selecting evaluation criteria, the second step assigned relative weights to each of the rating criteria, and the third step assigned point values in each of the selected criteria for each of the hazards. Evaluation Criteria Selection of evaluation criteria was accomplished by determining which aspects of specific hazards were of most concern to the community. This process was completed by assigning a level of importance ranging from Always Important to Not Worth Considering to each hazard aspect. Table 7.1 shows a complete list of all aspects considered in this process, and level of importance assigned by the committee. Hazard Aspect Likelihood of Occurrence Capacity to Cause Damage Size of Affected Area Speed of Onset Percent of Population Affected Potential for Casualties Potential for Negative Economic Effects Duration of Threat Seasonal Risk Pattern Environmental Impact Predictability of Hazard Ability to Mitigate Availability of Warning System Public Awareness Collateral Damage Always Very Important Table 7.1 Hazard Evaluation Criteria Usually Important Sometimes Important Rarely of Importance Not worth Considering Hazard Analysis Evaluation Measures Of the Hazard Aspects selected by the Committee, six were identified as being always very important. This process used these measures to evaluate each hazard facing the community. Those measures are: 1) likelihood of occurrence; 2) potential for causalities; 3) number of people effected; 4) ability to predict; 5) ability to mitigate; and 6) the area effected. Each 7-1

2 corresponding benchmark factor has been assigned a specific point value (10, 7, 4 or 1 point), based on each individual factor s relative severity and negative impacts. In recognition of the fact that some factors need to be given more consideration than others, each of the criteria was weighted. A percentage value has been assigned to each employed measure based on the relative significance of the measure in ranking the hazards. The sum of all of measures must equal 100 percent. The following is a synopsis of each hazard evaluation measure, weight and benchmark factor available to this analysis: Likelihood of Occurrence Likelihood of occurrence measures the frequency with which a particular hazard occurs. The more frequently a hazard event occurs, the more potential there is for damage and negative impact on a community. Size of Affected Area Each hazard affects a geographic area. For example, a blizzard might affect an entire state or even several states, while a flood might only affect a portion of a county or municipality. Although size of the affected area is not always indicative of the destructive potential of the hazard (a tornado is a good example), generally the larger the affected area, the more problematic the hazard event is to a community. Capacity to Cause Physical Damages The capacity to cause physical damages refers to the destructive capacity of the hazard. While the destructive capacity of some hazard events, such floods and tornadoes, is often immediate and readily apparent, some hazards may have significant destructive capacity that is less obvious as it may occur over a extended period of time such as extreme temperatures or drought. Speed of Onset Speed of onset refers to the amount of time it typically takes for a hazard event to occur. Speed of onset is an important evaluation measure because the faster an event occurs, the less time local governmental agencies typically have to warn the potentially impacted population of appropriate protective actions. Potential for Causing Casualties Potential for causing casualties refers to the number of casualties (deaths and injuries) that can be expected if a particular hazard event occurs. Percent of Population Effected Percent of Population affected refers to the percent of the county population that may be effected directly or indirectly by the hazard event. Economic Effects Economic effects are the monetary damages incurred from a hazard event and include both public and private damage. Direct physical damage costs, as well as indirect impact costs such as lost business and tax revenue, are included as part of the total monetary damages. Duration Duration refers to the time period the hazard event is actively present and causing damage (often referred to as the time on the ground.) Duration is not always indicative of the 7-2

3 damaging potential of a hazard event (a tornado is a good example). However, in most cases, the longer an event is active and thus causing damage, the greater the total damages will be. Seasonal Pattern Seasonal pattern refers to the time of year in which a particular hazard event can reasonably be expected to occur. Some hazard events can occur at any time of the year, while others occur primarily during one particular season (i.e., blizzards in winter). Oftentimes, hazard patterns coincide with peak tourism seasons and other times of temporary population increases, greatly increasing the vulnerability of the population to the negative impacts of certain hazard events. Predictability Predictability refers to the ease with which a particular hazard event can be predicted - in terms of time of occurrence, location, and magnitude. Predictability is important because the more predictable a hazard event is, the more likely it is a community will be able to warn the potentially impacted population and take other preventive measures to minimize loss of life and property. Collateral Damage Collateral damage refers to the possibility of a particular hazard event causing secondary damage and impacts. For example, blizzards and ice storms can cause power outages, which can cause loss of heat, which can lead to hypothermia and possible death or serious injury. Generally, the more collateral damage a hazard event causes, the more serious a threat the hazard is to a community. Environmental Impact Environmental Impact refers to the environmental damage that may be caused by a particular hazard event. The effects of a hazard event must be thought through to identify possible environmental impact. For example, a flood event may overwhelm a sewage treatment plant which then discharges raw sewage thereby contaminating water supplies. Availability of Warnings Availability of warnings indicates the ease with which the public can be warned of a hazard. This measure does not address the availability of warning systems in a community, per se. Rather, it looks at the overall availability of warning in general for a particular hazard event. For example, a community might receive warning that a flood will occur within 24 hours, but receive no warning when a large structural fire occurs. Generally, hazards that have little or no availability of warning tend to be more problematic for a community from a population protection and response standpoint. Mitigative Potential Mitigative potential refers to the relative ease with which a particular hazard event can be mitigated against through the application of structural or non-structural (or both) mitigation measures. Generally, the easier a hazard event is to mitigate against, the less of a future threat it may pose to a community in terms of loss of life and property. Public Awareness The amount of public awareness indicates the ease with which the public can be informed about particular hazards. This measure does not address the current level of public awareness that exists in the community. Rather, it looks at the overall value of public awareness in general for a particular hazard event. 7-3

4 Hazard Analysis Evaluation Benchmark Factors Likelihood of Occurrence Effected Area Excessive Occurrence 10 pts Large Area 10 pts High Occurrence 7 pts Small Area 7 pts Medium Occurrence 4 pts Multiple Sites 4 pts Low Occurrence 1 pt Single Site 1 pt Population Impact Percent of Population Affected High Impact 10 pts 60% to 100% 10 pts Medium Impact 7 pts 30% to 60% 7 pts Low Impact 4 pts 15% to 30% 4 pts No Impact (none) 1 pt 15% or less 1 pts Predictability Mitigative Potential Unpredictable 10 pts Easy to Mitigate 10 pts Somewhat Predictable 7 pts Possible to Mitigate 7 pts Predictable 4 pts Difficult to Mitigate 4 pts Highly Predictable 1 pt Impossible to Mitigate 1 pt 7-4

5 TABLE 7.2 OTSEGO COUNTY HAZARD RATING Evaluation Criteria Chance of Occurrence Population Effected Number of Casualties Ability to Predict Ability to Mitigate Area Effected Total Weight Must = 100% WEIGHT =========> 25% 15% 10% 15% 25% 10% 100% RANK Hazard Winter Weather Hazard Extreme Temperature Wildfire Transportation Accident Severe Winds Oil/Gas Well Incident Pipeline Accident Structural Fire Transportation Hazmat Fixed Site Hazmat Lightning Tornadoes Infrastructure Failure Public Health Nuclear Attack Hail Drought Terrorism/Sabotage/WMD Shoreline Flooding Scrap Tire Fire Earthquake Civil Disturbance Riverine Flooding Dam Failure Subsidence

6 Composite Hazard Ranking High to Moderate County Significance Winter Weather Hazards 8.15 Extreme Temperatures 7.65 Wildfire 6.60 Transportation Accidents 6.60 Severe Winds 6.35 Oil/gas Well Incident 6.00 Pipeline Accident Moderate to Low County Significance Structural Fire 5.65 Transportation Hazmat 5.35 Fixed Site Hazmat 5.10 Lightning 4.95 Tornado 4.60 Infrastructure Failure 4.45 Public Health 4.30 Nuclear Attack 4.15 Hail 4.10 Low County Significance Drought 4.0 Terrorism/sabotage/WMD 3.55 Shoreline Erosion 3.40 Scrap Tire Fire 3.00 Earthquake 2.90 Civil Disturbance 2.85 Riverine Flooding 2.75 Dam Failure 2.55 Subsidence 1.70 Risk Assessment and Vulnerability Assessment Summary Risk Assessment The goals of risk assessment are to determine where hazards exist, and develop an understanding of how often they will arise and how much harm they will cause in. Based on the weighted hazard ranking process recommended in the Michigan Hazard Analysis workbook, a composite of hazards and their relative risk are presented below. This list will be used as the foundation for developing hazard mitigation goals and strategies in subsequent chapters. High Risk: -- very likely to occur during hazard mitigation planning horizon of 20 years, and/or effect all or most of the county. Medium Risk: -- somewhat likely to occur during hazard mitigation planning horizon of 20 years, and/or effect a significant area of the County. Low Risk: -- means it is not likely to occur, or cover only a limited area within county. Vulnerability Assessment This step looks at such points as population concentrations, age-specific populations, development pressures, types of housing (older homes, mobile homes), presence of agriculture, sprawl (spreading 7-7

7 resources too thin), and other issues that may make more vulnerable to specific hazards. Basic criteria are listed below. Vulnerability assessment ratings for are prioritized and depicted in Table 7.3 High Vulnerability: -- If an event occurred it would have severe impacts over large geographic areas or more densely populated areas and have a serious financial impact on County residents and businesses. Medium Vulnerability: -- If an event occurred it would have confined impacts on the safety of residents but would have a financial impact on County residents and businesses. Low Vulnerability: -- If an event occurred it would have very minimal impact on the safety of County residents and minimal financial impact on County residents and businesses. Table 7.3, -- Risk and Vulnerability Assessment Summary Ranked Hazards in Risk Vulnerability Assessment Assessment Winter Weather Hazards High High Extreme Temperatures High High Wildfire High Med Transportation Accidents High Medium Severe Winds High Medium Structural Fire High Medium Oil/Gas Well Accident Medium Medium Pipeline Accident Medium Medium Transportation Hazmat Medium Medium Fixed Site Hazmat Medium Medium Tornados Medium Medium Public Health Medium Medium Drought Medium Medium Terrorism/Sabotage/WMD Medium Low Lightning Medium Low Hail Medium Low Riverine Flooding Medium Low Nuclear Attack Low High Dam Failure Low Low Shoreline Erosion Low Low Civil Disturbance Low Low Scrap Tire Fire Low Low Subsidence Low Low Earthquake Low Low 7-8

8 Vulnerable Situation in Winter Weather Hazards s central location in the northern tip off Michigan s Lower Peninsula, and more significantly its elevated exposure to winter winds off of Lake Micigan result in notable lake effect snow, especially during the period from October through mid-january. An excellent summary of the Lake Effect phenomenon in is describe in the book, Michigan: A Geography by Lawrance A. Sommers.. Lake-effect snow seldom falls in significant amounts further inland than about 40 miles, but it is accentuated where inland-moving snow clouds cross higher terrain, as in or on much of the Keweenaw Peninsula/Huron Mountains. The description and extent of these weather conditions are defined in Chapter 6 Although local residents are generally prepared to cope with these conditions, and State and local highway and police agencies are equipped to provide adequate response to often extreme travel conditions, the immediate and rapid onset of these conditions, can often be extremely hazardous. Northsouth running I-75 serves as the principal land-transport north-south artery in the state, and carry significant traffic all times of the year. In many cases it is not the extent or overall amount of snowfall, but the rapid change in encountered conditions. With the right combination of wind-speed and direction, white-out conditions can occur in otherwise clear conditions. Knowledge of these conditions through signs posted at critical positions along I-75 and other vulnerable state highways could provide warning of rapid deterioration of driving conditions to unsuspecting drivers. The National Oceanic and Atmospheric Administration (NOAA) office in Gaylord, Michigan has prepared a series of maps relating wind direction and the risk and distribution of Lake-Effect snow across the Northern Lower and Eastern Upper Peninsulas of Michigan. From this series of maps it becomes apparent that when winds are from the West-Northwest (Figure 7.1), Northwest (Figure 7.2), and to some extent West (Figure 7.3) directions,, especially along the I-75 corridor, is vulnerable to significant Lake-Effect snow, and often accompanying white-out conditions. 7-9

9 Figure 7.1, Lake Effect Snow Vulnerability, from West-Northwest Flow Source: NOAA, Gaylord, MI 7-10

10 Figure 7.2, Lake Effect Snow Vulnerability from Northwest Flow Source: NOAA, Gaylord Michigan 7-11

11 Figure 7.3, Lake Effect Snow Vulnerability from West Flow Source: NOAA, Gaylord Michigan 7-12

12 Actions involving public education and communication are important approaches toward mitigating this winter hazard to travelers, especially along I-75 in. A program to provide drivers traveling on major highways with current situational information at rest areas would be beneficial. NOAA is also urging use of road-signs, both portable and fixed, to warn travelers with direct and immediate warnings of changing road conditions. NOAA has the capability to predict with good accuracy when and where Lake Effect and white-out conditions will occur along specific sections of highway. Driver warnings located appropriately could significantly help to prepare the drivers for locally hazardous conditions. Wildfire The large number of permanent and seasonal homes in northeastern Michigan, coupled with the increase in tourists during the most dry (and therefore most vulnerable) times of the year, greatly increases the risk from wildfires. The threat of life and property losses related to wildfires is a significant issue for federal, state and local fire and planning agencies who consider the mix of residential areas and wildlands. The wildland fire threat is part of the more general consideration of human development encroaching wildlands. The March, 2000, edition of the Journal of Forestry reflects this with urban encroachment and wildland fragmentation the principal subject with residential fire one of the specific issues. (Cohen 2000). Presently, the wildland fire threat to homes influences fire management and protections policies at national and local levels. (Jack D. Cohen, What is the Wildland Fire Threat to Homes?) Current research indicates lowering building ignition potential will significantly reduce chances of home destruction without extensive wildland fuel reduction. This becomes an issue of homeowner education and community involvement. Community/homeowner understanding of the methods of lowering home ignition potential is the primary mitigative action to reduce wildland fire threat to residential areas. As part of a nationwide effort to identify communities at high risk the following federal agencies developed a list of urban wildland interface communities in the vicinity of Federal lands that are at high risk from wildfire: Forest Service, Department of Agriculture; Bureau of Indian Affairs, Bureau of Land Management, Fish and Wildlife Service, and National Park Service, Department of the Interior. This was published in the Federal Register / Vol. 66, No. 160 / Friday, August 17, 2001; Urban Wildland Interface Communities within the Vicinity of Federal Lands that are at High Risk from Wildfire. State of Michigan, along with many other states, felt the urban wildland interface is not limited to communities in the vicinity of Federal land and developed a comprehensive state list of communities at risk. It is important to note that the urban wildland interface is not limited to communities in the vicinity of Federal land. Many States, particularly in the East, submitted revised community lists that included all interface communities in their State, regardless of their relationship to Federal land. These States felt strongly that the full, nationwide scope of the urban wildland interface problem must be conveyed. Otsego abuts both Crawford and Oscoda counties to the south and southwest respectively. These highest risk areas are concentrated primarily in the state forest areas located in southeast quadrant of the County in Charlton and Chester Townships, with another less extensive area in the northeast quadrant of the county. The combined area of Charlton and Chester Townships is 115,200 acres. Total year round population for these counties is 2,646 or about 15 persons/square mile. Of the 2,386 housing units in this area, about 49% are seasonal structures, primarily vacation/hunting property. 7-13

13 To adequately institute practices of lowering home ignitability it will require changing relationships between homeowners and local fire services. Instead of all fire protection responsibilities being with fire agencies, homeowners should take primary responsibility for adequately lowering home ignitability. The role of fire protection agencies becomes that of a community partner to provide homeowners the technical assistance needed to reduce home ignitability. To be successful, this partnership arrangement must be shared and implemented equally by homeowners and fire services. Projects designed to mitigate the threat of wild fire should evolve from the concepts and materials represented by Firewise. Firewise is a cooperative effort among federal, state, and private agencies and organizations to promote fire safety in the wildland/urban interface. The primary Firewise tenet is that it is unnecessary to lose homes or other buildings in wildfires if those homes or buildings are built and maintained according to simple Firewise principles. Firefighters cannot be everywhere when a wildfire occurs, but if homeowners follow Firewise suggestions, homes and buildings will survive wildfires without any firefighters being there to protect them. The Firewise program addresses the risk to homes in the wildland/urban interface to wildland fire and provides a potential vehicle upon which a partnership between homeowners and fire services can develop The Firewise program encourages landowners that currently live or are thinking about living in a wildland or forested area to prepare for wildfire in order to minimize risk. The fundamental steps are: When building a new home, choose a Firewise location. Design, build and renovate structure using Firewise guidelines Stay on guard with Firewise landscaping and maintenance procedures. Information about Firewise can be found at

14 Figure 7.4 Wildfire Prone Areas 7-15