2013 Update to the State of Montana Multi-Hazard Mitigation Plan and Statewide Hazard Assessment
4.0 RISK ASSESSMENT
The Risk Assessment portion of this document provides a detailed description of the hazards in
Montana, an assessment of the State’s vulnerability to those hazards, and a basis for the
mitigation goals and activities proposed in the Mitigation Strategy portion of the document. This
Risk Assessment section examines natural and man-made hazards that can impact the State,
determines which areas of the State are most vulnerable to each hazard, and estimates
potential losses to State facilities for each hazard.
4.1
HAZARD IDENTIFICATION
A database of historical hazard events was developed using a variety of sources to identify all
hazards commonly recognized as threats to the State. The research was very thorough and
involved such organization as Montana DES, the National Climatic Data Center (NCDC) Storm
Events Database and Spatial Hazard Events and Losses Database for the United States
(SHELDUS), as described below, records of past Federal and State disaster declarations were
reviewed to determine the most significant hazard events causing loss of life and property.
The NCDC Storm Events database receives Storm Data from the National Weather Service
(NWS). The NWS service receives their information from a variety of sources, including County,
State and Federal emergency management officials, local law enforcement officials, skywarn
spotters, NWS damage surveys, newspaper clipping services, the insurance industry and the
general public. Storm Data is an official publication of the National Oceanic and Atmospheric
Administration (NOAA) which documents the occurrence of storms and other significant weather
phenomena having sufficient intensity to cause loss of life, injuries, significant property damage,
and/or disruption to commerce.
SHELDUS is a county-level hazard data set for the United States for 18 different natural hazard
events types. For each event the database includes the date, location, property losses, crop
losses, injuries, and fatalities that affected each county. The database includes every loss
causing and/or deadly event between 1960 through 1975 and from 1995 onward. Between 1976
and 1995, SHELDUS reflects only events that caused at least one fatality or more than $50,000
in property or crop damages.
Prior knowledge of risks associated with each hazard summarized in the original Plan (2004)
stemmed from a series of Hazard Technical Advisory Group and Stakeholder Meetings, which
included statewide experts in resource management, emergency services and disaster
mitigation. Review of the previous Plan helped form a framework for the discussions and the
identification of hazards. As part of the update process, all of the hazards profiled in the original
Plan were closely examined by the SHMO and Contractor, and validated by the Planning Team
with regard to the following considerations:
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Prior knowledge of the relative risk associated with each of the hazards;
Hazard events occurring within the last three years;
Comparison to hazards identified in local jurisdiction plans; and
The ability to effectively mitigate the hazard via the DMA 2000 process.
The hazard profiles in the local County and Tribal hazard mitigation plans were evaluated to
help determine statewide risk. The presumption was that the importance given to hazards by the
local communities would and should correlate to priorities for the State. As of April 1, 2013,
Montana had 43 approved county and two approved tribal PDM Plans in good standing. Twelve
(12) county plans and three tribal plans are in the update process and one county and two tribal
plans have expired with no update underway. One Montana county (Meagher) has never
completed a PDM Plan. Where available, hazard information from the local plans has been
incorporated into the State Plan. In addition, electronic links to local plans for 55 of Montana’s
56 Counties (Meagher County has not completed a PDM Plan) and 7 Tribal Nations are
provided in Appendix D.
The Risk Assessment in the 2013 State Hazard Mitigation Plan focuses on the hazards listed
below, as outlined in subsequent sections of this chapter:
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Communicable Disease
Dam Failure
Drought
Earthquakes
Flooding
Hazardous Material Incidents
Landslides
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Severe Summer Weather (formerly Severe
Thunderstorms, Hail, Wind and Tornadoes)
Severe Winter Weather (formerly Winter Storms and
Avalanches)
Terrorism
Volcanic Eruptions
Wildland and Rangeland Fires
Three hazards were de-emphasized in the 2010 State Hazard Mitigation Plan; communicable
disease, drought, and terrorism/violence because they were covered by plans administered by
other State or Federal agencies or couldn’t be mitigated through the DMA 2000 process. These
hazards were re-incorporated into the State PDM Plan as part of 2013 update at the request of
the SHMO.
4.2
HAZARD RANKING
For the 2013 State PDM Update, hazards were ranked using the Calculated Priority Risk Index
(CPRI). The CPRI examines four criteria for each hazard (probability, magnitude/severity,
warning time, and duration (Table 4.2-1). For each hazard, an index value is assigned for each
CPRI category from 0 to 4 with “0” being the least hazardous and “4” being the most hazardous
situation. This value is then assigned a weighting factor and the result is a hazard ranking
score. The SHMO initially completed the hazard ranking and the scores were validated by the
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Planning Team. Table 4.2-2 presents the results of the CPRI scoring for all hazards with a
cumulative score sheet included in Appendix C.
TABLE 4.2-1
CALCULATED PRIORITY RISK INDEX
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TABLE 4.2-2
CALCULATED PRIORITY RANKING INDEX SUMMARY
Hazard
Probability
Wildland and Rangeland Fire
Earthquake
Severe Summer Weather
Flooding
Severe Winter Weather
Communicable Disease
Hazardous Material Incidents
Drought
Dam Failure
Landslides
Terrorism/Violence
Volcanic Eruptions
Highly likely
Likely
Highly likely
Highly likely
Highly likely
Highly likely
Highly likely
Highly Likely
Possible
Possible
Unlikely
Unlikely
Magnitude
and/or
Severity
Critical
Catastrophic
Critical
Critical
Critical
Critical
Limited
Limited
Limited
Negligible
Limited
Negligible
Warning Time
Duration
CPRI Score
< 6 hours
< 6 hours
< 6 hours
12-24 hours
12-24 hours
> 24 hours
< 6 hours
> 24 hours
6-12 hours
< 6 hours
< 6 hours
< 6 hours
> 1 week
> 1 week
< 24 hours
> 1 week
> 1 week
> 1 week
< 24 hours
> 1 week
< 1 week
< 1 week
> 1 week
> 1 week
3.70
3.55
3.50
3.40
3.40
3.25
3.20
2.95
2.25
2.10
2.05
1.75
The SHMO elected to prioritize the flooding hazard due to historic high damages and high
frequency and eliminate tie scores in the hazard ranking; therefore, the hazard ranking for the
2013 Montana State PDM Plan is presented below. The hazard profiles are arranged in the
remainder of this section by rank.
1 – Wildland and Rangeland Fire (Plan Section 4.4.1)
2 – Flooding (Plan Section 4.4.2)
3 – Earthquakes (Plan Section 4.4.4)
4 – Severe Summer Weather (Plan Section 4.4.3)
5 – Severe Winter Weather (Plan Section 4.4.5)
6 – Communicable Disease (Plan Section 4.4.6)
7 – Hazardous Material Incidents (Plan Section 4.4.7)
8 – Drought (Plan Section 4.4.8)
9 – Dam Failure (Plan Section 4.4.9)
10 – Landslides (Plan Section 4.4.10)
11 – Terrorism (Plan Section 4.4.11)
12 – Volcanic Eruptions (Plan Section 4.4.12)
Table 4.2-3 compares the hazard ranking from the 2010 to the re-ranking for 2013 Montana
State PDM Plan.
TABLE 4.2-3
CHANGE IN HAZARD RANKING: 2010 TO 2013
Hazard
Wildland and Rangeland Fire
Flooding
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2010 Ranking
1
3
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2013 Ranking
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TABLE 4.2-3
CHANGE IN HAZARD RANKING: 2010 TO 2013
Hazard
Earthquake
Severe Summer Weather
Severe Winter Weather
Communicable Disease
Hazardous Materials Incidents
Drought
Dam Failure
Landslides
Terrorism/Violence
Volcanic Eruptions
4.3
2010 Ranking
2
4(tie)
5 (tie)
not ranked
5 (tie)
not ranked
4 (tie)
5 (tie)
not ranked
5 (tie)
2013 Ranking
3
4
5
6
7
8
9
10
11
12
ASSESSING VULNERABILITY
The vulnerability assessment provided in the original Plan and 2007 update was largely revised
and replaced in the 2010 update. The completion of most all of the county and tribal hazard
mitigation plans has resulted in additional data being available for evaluating the State’s
vulnerability to hazards. The 2013 State Plan update builds on what was presented in 2010 by
incorporating data from recently completed original PDM plans and plan updates, determining
spatial components (latitude/longitude)for State-owned critical facilities for analysis, data from
the 2010 census, and assessor data from the Montana Department of Revenue (DOR)
Cadastral Mapping Program. The GIS-based risk assessment template methodology to
estimate loss (Appendix B) has also been updated.
Methodologies for assessing hazard vulnerability vary depending upon the hazard, the type of
losses that can be incurred, and available data. For some hazards, models have been
developed to assess the potential vulnerability and calculate losses. For others, the vulnerability
is qualitative and potential losses can only be assessed in a very general nature. Potential
losses were analyzed at both the state and local level. The hazard assessment identifies the
exposure in structure value and content value for State-owned facilities. Hazard exposure at the
local level is based on structure value, society risk and potential economic loss, as detailed in
the local hazard mitigation plans reviewed.
Vulnerabilities are described in terms of critical facilities, infrastructure, building stock
(residential, commercial and industrial structures), and population affected by the hazard.
Hazard impact areas describe the geographic extent a hazard can impact a jurisdiction and are
uniquely defined on a hazard-by-hazard basis. Mapping of the hazards, where spatial
differences exist, allows for hazard analysis by geographic location.
The methods used in this risk assessment represent the best readily-available statewide data.
Table 4.3-1 describes the methods used to assess vulnerability and losses across the state.
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Hazard
Wildland and
Rangeland Fires
Flooding
Earthquake
Severe Summer
Weather
Severe Winter
Weather
Communicable
Disease
Hazardous Material
Incidents
Drought
Dam Failure
Landslide
Terrorism and
Violence
Volcanic Eruptions
Montana DES
TABLE 4.3-1
VULNERABILITY ASSESSMENT METHODS
Vulnerability Assessment Methods
A GIS layer of WUI layers from local CWPPs, available from DNRC, was used in the
PDM analysis. This wildfire hazard layer was intersected with MDOR assessor data
and spatially located critical facilities and bridges to determine building and
infrastructure exposure. The hazard layer was also intersected with 2010 census
tract data to determine population exposure.
A GIS layer was created of a HAZUS-derived flood risk area enhanced with data from
DFIRM maps. This flood hazard layer was intersected with MDOR assessor data and
spatially located critical facilities and bridges to determine building and infrastructure
exposure. The hazard layer was also intersected with 2010 census tract data to
determine population exposure.
A GIS layer was created by digitizing Peak Ground Acceleration seismic zones
compiled by the U.S. Geological Survey. This earthquake hazard layer for 18%g and
greater was intersected with MDOR assessor data and spatially located critical
facilities and bridges to determine building and infrastructure exposure. The hazard
layer was also intersected with 2010 census tract data to determine population
exposure. Results are presented of the Tier 1 seismic evaluations of state-owned
critical facilities in the Intermountain Seismic Belt.
A GIS layer was created from point data provided by the NWS of tornados, hail over
.75 inches, and thunderstorm wind over 50 knots. This severe summer weather
hazard layer was intersected with MDOR assessor data to determine building
exposure. The hazard layer was also intersected with 2010 census tract data to
determine exposure to vulnerable population.
Severe winter weather is considered to have a uniform risk across the State and was
therefore, generally analyzed in the risk assessment. Historic data was used to
calculate hazard frequency and magnitude. This percentage was then applied to
building stock and critical facility data, and the 2010 Census to calculate annualized
loss to property and population.
The communicable disease is considered to have a uniform risk across the State and
was therefore, generally analyzed in the risk assessment.
A GIS layer was created by buffering the state’s highways, railroads and toxic release
facilities by 0.25 mile. This hazardous material hazard layer was intersected with
MDOR assessor data and spatially located critical facilities and bridges to determine
building and infrastructure exposure. The hazard layer was also intersected with
2010 census tract data to determine population exposure.
The drought hazard has a variable risk across the State that changes on a monthly
basis. Therefore, it is only analyzed on a general basis in the risk assessment.
A GIS layer was created of the inundation areas, digitized from EAPs, associated
with federal, state, local and private high hazard dams. This dam failure hazard layer
was intersected with MDOR assessor data and spatially located critical facilities and
bridges to determine building and infrastructure exposure. The hazard layer was also
intersected with 2010 census tract data to determine population exposure.
A GIS layer was created by digitizing a landslide risk map compiled by the U.S.
Geological Survey which considers topography, geology, and past landslide data.
The landslide hazard layer was intersected with MDOR assessor data and spatially
located critical facilities and bridges to determine building and infrastructure
exposure. The hazard layer was also intersected with 2010 census tract data to
determine population exposure.
The terrorism hazard is considered to have a uniform risk across the State. Montana
DES completed a Threat Hazard Identification Risk Assessment (THIRA) in
December 2012. The THIRA is included as an appendix to the State PDM Plan to
address the Terrorism hazard.
The volcanic ash hazard was generally analyzed in the risk assessment. Counties
located adjacent to Yellowstone Park are considered vulnerable to impacts from
volcanic eruptions, mudflows, and ashfall. Counties west of the Continental Divide
are considered vulnerable to impacts from volcanic eruptions in the Cascade Range
in Washington State.
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The methodology used in risk calculations presents a quantitative assessment of the
vulnerability of the building stock, population, and critical facilities to individual hazards and
cumulatively to all hazards. Parcel data, available from the Montana Department of Revenue’s
Cadastral Mapping Program, was used in the analysis. This data spatially recognizes residential
and “other” (commercial, agricultural, and industrial) land parcels along with the number of
structures and appraised value of building stock (2012 data). Using GIS, hazard areas were
intersected with the parcel data to identify the exposure (number and value of buildings) at risk
from each hazard. It should be noted that if any part of the parcel was clipped by the hazard
layer, the value and number of structures in that parcel were assumed to be located in the
hazard area. This can lead to over reporting of exposure where parcels are large. Using GIS,
hazard risk areas were also intersected with spatially located critical facilities to determine the
exposure of those at risk to from each hazard. State-owned bridges were also included in the
critical facility vulnerability analysis.
Population exposure was computed using data from the 2010 census. Using GIS, census block
data was intersected with the hazard areas to determine population at risk. If any part of the
census block was clipped by the hazard layer, the number of residents in that census block was
assumed to reside in the hazard area. It should be noted that this may lead to over reporting
where census blocks are large. Population exposure is reported according to total population
living in the hazard area and individuals under the age of 18 years. Population over the age of
65 and living below the poverty level were not available on the census block level and were
therefore, not included in the analysis. It should be noted that there are some inherent
inaccuracies using this approach.
For hazards that are uniform across the jurisdiction (i.e. severe winter weather) the methodology
presented below was used to determine annualized property loss.
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Exposure x Frequency x Hazard Loss Magnitude
Where:
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Exposure = building stock or critical facilities at risk
Frequency = annual number of events determined by calculating the number of hazard
events / period of record
Magnitude = percent of damage expected calculated by: (property damage/# incidents)/
total building stock or critical facilities
For the hazards with regional variability and damage data (e.g. wildfire, flooding, severe
summer weather, and hazardous material incidents) the hazard area factored into the annual
loss estimation calculations.
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For hazards without documented property damage (dam failure, landslide), magnitude could not
be calculated and therefore, only the exposure of the building stock or population was
computed.
Vulnerability tables within the hazard profiles present the risk assessment results by DES
District, and for counties and cities/towns experiencing the greatest exposure and population
growth. The DES Districts are presented in Figure 4.3-1. Information from the local risk
assessments was analyzed on a plan-by-plan basis with exposure data for each hazard
recorded on a spreadsheet (see Local Plan Exposure Summaries in Appendix B) and
compared with the analysis done as part of the State PDM Plan update. Each hazard profile
contains a section entitled Review of Potential Losses in Local PDM Plans where the analysis
comparison is presented.
Probability of a hazard event occurring in the future was assessed based on hazard frequency
over a 100 year period. Hazard frequency was based on the number of times the hazard event
occurred divided by the period of record. If the hazard lacked a definitive historical record, the
probability was assessed qualitatively based on regional history and other contributing factors.
Probability was broken down as follows:
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Highly Likely – greater than 1 event per year (frequency greater than 1).
Likely – less than 1 event per year but greater than 1 event every 10 years (frequency
greater than 0.1 but less than 1).
Possible – less than 1 event every 10 years but greater than 1 event every 100 years
(frequency greater than 0. 01 but less than 0.1).
Unlikely – less than 1 event every 100 years (frequency less than 0.01)
While loss estimates are presented as dollar values and number of structures or people affected
they should not be interpreted literally. Due to data and modeling limitations the values
presented may be biased high side when parcel size and census blocks are large.
4.4
HAZARD PROFILES
Hazard profiles include a description of the hazard and the history of occurrence, the
vulnerability and area of impact, and the probability and magnitude of future events. The hazard
profile identifies State-owned and operated facilities and infrastructure that are most vulnerable
to the hazard, where possible. Risk assessment results were used to formulate the State’s
mitigation strategies. The remainder of this section presents hazard profiles according to their
CPRI score – highest ranking hazard to lowest. Section 4.5 is a risk assessment summary.
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Figure 4.3-1 Montana Disaster & Emergency Services Districts
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