1. Describe Hazards

Element B1

The risk assessment shall include a description of the type, location and extent of all natural hazards that can affect the jurisdiction.

44 CFR §201.6(c)(2)(i)

The plan must include a description of the natural hazards that affect the jurisdiction(s) in the planning area. The following provides suggestions for identifying hazards in the planning area:

  • Review your State Hazard Mitigation Plan for information on hazards affecting the planning area.
  • Document the disaster declaration history.
  • Download weather-related events from online resources, such as the National Climatic Data Center.
  • Review existing studies, reports, and plans related to hazards in the planning area. State and federal agencies are also good sources for hazard-related information.
  • Use flood insurance rate maps (FIRM) and non-regulatory flood risk assessment products developed for your community by FEMA as part of the National Flood Insurance Program (NFIP) and the RiskMAP program.
  • Contact colleges or universities that have hazard-related academic programs or extension services.
  • Interview your planning team and stakeholders about which hazards affect the planning area.
  • Consult local resources such as the newspaper, chamber of commerce, local historical society or other resources with records of past occurrences.
  • For plan updates, reference hazards previously identified and determine if they are still relevant.

If your plan omits a natural hazard that is commonly recognized to affect the planning area, it must include the planning team’s rationale for the omission. For example, a hazard may be possible, but the likelihood and magnitude are so minimal that the planning team decides not to provide a detailed description or risk assessment.

Hazard Descriptions

For each hazard affecting the planning area, the risk assessment must include a description of location, extent, previous occurrences, and probability of future events. Plan updates will incorporate any additional hazards that have been identified and any new data that has become available, such as new flood studies. Plan updates must include hazard events that have occurred since the last plan was completed.

Location. Location is the geographic areas within the planning area that are affected by the hazard, such as a floodplain. Hazard areas may be further defined, such as high wildfire hazard areas versus low wildfire hazard areas. The entire planning area may be uniformly affected by some hazards, such as drought or winter storm. Although maps are usually the best way to illustrate location for many hazards, location may be described in other formats, such as a narrative.

Best Practice

King County, WA

King County’s Hazard Mitigation Plan was identified as a best practice because it mapped the 100-year and 500-year flood zones in the planning area.


Pinellas County, FL

Pinellas County’s plan included a map identifying areas that would be affected by storm surges of various categories of hurricanes.


San Francisco, CA

CCthermSan Francisco’s plan did an excellent job of incorporating potential effects of climate change into its hazard identification and analysis. It incorporated the findings of a recent study by the city’s Public Health Department that produced a heat vulnerability map of the city. The vulnerability index created included twenty social, geographical and environmental variables. For more information on the creation of the index see the Public Health Department’s website.

San Francisco

Tulsa, OK

Tulsa was identified as a best practice because it displayed the areas of highest concern for wildfire on a map of the planning area.


Extent. Extent is the strength or magnitude of the hazard. Extent can be described in a combination of ways depending on the hazard, such as:

  • The value on an established scientific scale or measurement system, such as EF2 on the Enhanced Fujita Scale for tornadoes or 5.5 on the Richter Scale for earthquakes.
  • Other measures of magnitude, such as water depth or wind speed.
  • The speed of onset. For example, hurricanes have longer warning times, giving people and governments more time to prepare and evacuate, while earthquakes occur without warning.
  • The duration of hazard events. For most hazards, the longer the duration of an event, the greater the extent. Flooding that peaks and retreats in a matter of hours is typically less damaging than flooding of the same depth that remains in place for days.

Extent can be described using a map and/or narrative. Describing the extent of a hazard is not the same as describing its potential impacts on a community. Extent defines the characteristics of the hazard regardless of the people and property it affects, while impact refers to the effect of a hazard on the people and property in the community and will be addressed later in Task 5.

Element B2

The risk assessment shall include information on previous occurrences of hazard events and on the probability of future hazard events.

44 CFR §201.6(c)(2)(i)

Previous occurrences. The plan must include the history of previous hazard events for each hazard. This information helps estimate the likelihood of future events and predict potential impacts. For some hazards, it may be helpful to compile past events in tables. When data is available, describe the extent of the event and impacts, such as fatalities and injuries, building and infrastructure damages, and loss of services. Understanding the extent and impacts of past hazard events will help you anticipate potential damage from future events.

Best Practice

Morehead City, NC

Morehead City was chosen as a best practice because it included a table with basic statistics on events dating back to 1886.  It clearly illustrated the likelihood (i.e. average number of events a year) of the hazard, seen below.




Harris County, TX

Harris County’s plan included a map of the paths of major hurricanes since 1900.


Lake County, IL

Lake County was chosen as a best practice because it  maps the occurrences of past hazards. The map below displays the historical occurrences of lightning strikes in the planning area.

lake county lightning

Probability of future events. Probability is the likelihood of the hazard occurring in the future and can be described in a variety of ways. Probability may be defined using historical frequencies or statistical probabilities. Statistical probabilities often refer to events of a specific size or strength. For example, the likelihood of a flood event of a given size is defined by the percent chance in a single year, such as the one-percent annual chance of flood, also known as a 100-year flood. Hazard likelihood can also be compared using general descriptions or rankings. If general descriptors are used, then they must be defined in the plan. For example, “highly likely” could be defined as occurring every 1-10 years, “likely” as occurring every 10-50 years, and “unlikely” as occurring at intervals greater than 50 years. Some hazards are most likely during a specific time of year, but others can occur at any time. For example, in the West, flooding might be more frequent in the spring because of snow melt or, in the East, in late summer or fall during the hurricane season.

Climate Change

Climate Change and Climate Adaptation

Climate Change: A statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.

Climate Change Adaptation: The adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects.

Source: Intergovernmental Panel on Climate Change (IPCC), http://www.ipcc.ch/index.htm.

The planning team may decide to include a discussion of the impacts of climate change in the risk assessment. This is not required by federal mitigation planning regulation, but can provide a better understanding of how risk may change in the future. Climate change in and of itself may not be a hazard, but it may change the characteristics of the hazards that currently affect the planning area. For example, climate change may lead to more frequent and intense storms.  The planning team can include climate change as a separate section in the plan or within the descriptions of the existing hazards, such as severe storms, flooding, wildfire, and drought. Climate adaptation strategies, which are adjustments in natural or human systems to mitigate the impacts of a changing environment, may complement other hazard mitigation strategies. For an overview of potential changes in your region, consider reviewing the United States Global Change Research Program’s Regional Climate Change Impacts reports.

Best Practice

CCthermLewes, DE

Lewes was identified as a best practice because its plan integrates hazard mitigation and climate change adaptation. The plan describes how each identified natural hazard could be impacted by climate change. The excerpt below describes the potential impacts of climate change on winter storm events.

Winter Storms

Currently there are two climate change impacts that are likely to affect winter storms in Lewes. First, it is believed that precipitation in the winter will become more episodic with it falling in more extreme events. These extremes could exacerbate current winter storms making the overall effects of the storms worse. Additionally, the increase in average temperature will likely cause a reduction in the amount of precipitation falling as snow or ice as that precipitation will likely fall as rain instead. When snow and ice are reduced and the increased episodic precipitation is rain, Lewes could see an increase in inland flooding during winter storm events.

Technological Hazards and Human-Caused Threats

Threat and Hazard Identification and Risk Assessment (THIRA)

A THIRA incorporates technological and human-caused threats in addition to natural hazards. Similar to the risk assessment process described here, a THIRA describes the types of risk and gives them context, such as probability and likelihood. The process for conducting a THIRA results in a set of capability targets for all stages of emergency management, including prevention, protection, mitigation, response and recovery. The THIRA may be completed separately or build on the mitigation plan risk assessment, or HIRA, which further defines a community’s vulnerability to hazards, particularly for the built environment.

The planning team may decide to include technological hazards and human-caused threats in the plan, although this is not required by federal regulations. Technological hazards result from accidents or the failure of systems and structures, such as hazardous materials spills or airplane accidents. Human-caused incidents, also known as threats, result from intentional actions of an adversary, such as a chemical or cyber attack. A Threat and Hazard Identification and Risk Assessment (THIRA) expands on the existing hazard identification and risk assessment of a local mitigation plan; provides a comprehensive approach for assessing risks and associated impacts with all types of threat or hazard; and identifies a methodology for assessing a broader range of capabilities for prevention, protection, response and recovery and mitigation.

See Integrating Manmade Hazards into Mitigation Planning (FEMA 386-7) for suggestions and information on including these types of hazards and threats in the mitigation plan.

Best Practice

Augusta, GA

Augusta was selected as a best practice because it contains a section on technological hazards. Although the plan focuses on the location of hazardous material sites, it evaluates the risks relative to floodplains in the area. The map shown below, was including in the plan, and shows hazardous materials sites and floodplains as determined by FEMA.



CCthermBarnstable County, MA

Barnstable County, MA was chosen as a best practice because the plan includes extensive data on possible hazardous effects of climate change in the US in graphical and descriptive forms. The plan focuses on shoreline change and heavy downpours characterizing the hazards highly likely and likely respectively and of catastrophic and significant magnitudes respectively, as shown in the excerpt of the table below.

Barnstable County Best Practice
The plan also includes data from a study of Cape Cod’s shoreline from the mid 1800’s until 1994. The study identifies areas that have been eroding and accreting over time. The figure below shows the average annual shoreline change rates in feet per year.

Barnstable County Best Practice

The primary natural causes of erosion in Massachusetts are relative sea-level rise, which is presently approximately one vertical foot every 100 years, and coastal storms.

Overall, this Plan represents an understanding of climate change based on intergovernmental panel on climate change (IPCC, 2007).


Baltimore, MDCCtherm

Baltimore’s hazard mitigation plan was identified as a best practice because it uses clear graphics to explain the fairly complicated scientific causes of sea level rise.

Baltimore, MD Best Practice