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<br />16-1 <br />CHAPTER 16. <br />PLANNING AREA RISK RANKING <br /> <br />A risk ranking was performed for the hazards of concern described in this plan. This risk ranking assesses <br />the probability of each hazard’s occurrence as well as its likely impact on the people, property, and economy <br />of the planning area. The risk ranking was conducted via facilitated brainstorming sessions with the steering <br />committee. Estimates of risk were generated with data from HAZUS-MH using methodologies promoted <br />by FEMA. The results are used in establishing mitigation priorities. <br />16.1. PROBABILITY OF OCCURRENCE <br />The probability of occurrence of a hazard is indicated by a probability factor based on likelihood of annual <br />occurrence: <br />• High—Hazard event is likely to occur within 25 years (Probability Factor = 3) <br />• Medium—Hazard event is likely to occur within 100 years (Probability Factor =2) <br />• Low—Hazard event is not likely to occur within 100 years (Probability Factor =1) <br />• No exposure—There is no probability of occurrence (Probability Factor = 0) <br />The assessment of hazard frequency is generally based on past hazard events in the area. Table 16-1 <br />summarizes the probability assessment for each hazard of concern for this plan. <br />Table 16-1. Probability of Hazards <br />Hazard Event Probability (high, medium, low) Probability Factor <br />Avalanche High 3 <br />Dam Failure Low 1 <br />Drought High 3 <br />Earthquake High 3 <br />Flood High 3 <br />Landslide High 3 <br />Severe Weather High 3 <br />Volcano Low 1 <br />Wildfire High 3 <br /> <br />16.2. IMPACT <br />Hazard impacts were assessed in three categories: impacts on people, impacts on property and impacts on <br />the local economy. Numerical impact factors were assigned as follows: <br />• People—Values were assigned based on the percentage of the total population exposed to the <br />hazard event. The degree of impact on individuals will vary and is not measurable, so the <br />calculation assumes for simplicity and consistency that all people exposed to a hazard because <br />they live in a hazard zone will be equally impacted when a hazard event occurs. It should be <br />noted that planners can use an element of subjectivity when assigning values for impacts on <br />people. Impact factors were assigned as follows: