Unit 1: Hazard and Risk
Identifying the differences between hazards and risks is key to understanding how we react, mitigate, and live with natural disasters. This unit will begin with a discussion on identifying the differences between hazards and risk. Students will learn that hazards are the phenomenon while risk is the likelihood of that phenomenon affecting a particular region. Next, students will read an article that puts risk into context and participate in an in-class discussion. The unit will finish by having students calculate personal risk using a simple mathematical formula.
- Define hazard and risk.
- List examples of natural hazards and risks.
- Compare natural hazards and the frequency of their occurrence.
- Calculate personal risk from natural hazards.
This unit relates to:
- Earth scientists use repeatable observations and testable ideas to understand and explain our planet (Earth Science Literacy Big Idea 1).
- Natural hazards pose risks to humans (Earth Science Literacy Big Idea 8).
Context for Use
This unit may be used as an introduction to the Natural Hazards and Risks: Hurricanes module, or as a stand-alone introduction to the concepts of hazard and risk. It can be taught in any course discussing natural hazards or can be modified to fit a variety of earth, atmospheric, and marine science courses. The activities included in this unit are appropriate for introductory-level college students or as the basis for more in-depth class discussions on hazards and risks for upper-level students.
Description and Teaching Materials
Assign the following activity Student Handout (Acrobat (PDF) 284kB Aug27 14) as a pre-class homework assignment. In this assignment, students will consider the following questions:
- In the cartoon what are the hazards?
- How could the parachutist reduce her risk from the hazards?
Have students record their answers to these questions and be ready to discuss their responses.
This will help students visualize the difference between hazard (the phenomenon capable of causing harm to humans) and risk (likelihood and cost of those hazards happening to an individual or group).
Have students share their answers to the pre-class activity (Student Handout for Hazard or Risk Warm-up (Acrobat (PDF) 284kB Aug27 14)) and record answers on the board. The following are example student responses to the pre-class activity prompts:
In this cartoon what are the hazards?
How could the parachutist reduce her risk from such hazards?
Have students read the following essay by Jared Diamond, "That Daily Shower Can Be a Killer."
Display the following prompts on the board (prompts are located on a slide in the Unit 1 Presentation (PowerPoint 2007 (.pptx) 2.6MB Aug25 14)):
- What do you think is the natural hazard you encounter most frequently? Is it the one from which you perceive the most personal risk?
- Thinking of Diamond's example of New Guineans not sleeping under dead trees, what is at least one thing we do as a society to reduce risk to the natural hazard you listed above?
Have students consider these questions while reading the article. When all the students have finished reading the article, have them discuss their responses as a think-pair-share before polling the whole class for input.
After discussing the students' responses, the instructor can initiate a discussion on fatalities from the eight most common weather-related natural hazards (a table below in the Teaching Notes and Tips section lists 2013 and 10-year averages).
How is risk defined? Insurance companies use a simple formula to decide how to charge individuals for financial coverage from natural disasters. Students will calculate both the financial and human risk associated with a natural disaster.
Ask students to think about and write down how they would calculate the risk associated with a natural hazard.
Students will learn to calculate risk with Unit 1 Presentation (PowerPoint 2007 (.pptx) 2.6MB Aug25 14). Have students complete Student Handout for Calculating Risk (Microsoft Word 810kB Sep2 16) in pairs, small groups, or individually. The formula for calculating risk, definitions of key terms, and an example problem are listed below in the Teaching Notes and Tips section.
(Optional) If time allows, have students compare and contrast the financial and human risk of certain natural disasters. Some important questions to have students consider are:
- Are there discrepancies between the financial and human risk associated with certain natural disasters?
- Is it more important to consider the financial or human risk associated with natural disasters, or both?
Optional: If the in-class discussion from Activities 1.1 and 1.2 consume too much class time, the attached presentation and student handout about calculating risk can be assigned as homework.
Teaching Notes and Tips
Pre-Class Activity/Activity 1.1
If time allows, this activity can also be completed in class by handing out this student version Student Handout (Acrobat (PDF) 284kB Aug27 14) of the cartoon or utilizing the PowerPoint to facilitate student discussions.
There are many other creative interpretations of the hazards and risks portrayed in this cartoon. After listing the specific hazards and risks students generate, an instructor can summarize by giving straightforward definitions of the terms (see Unit 1 Presentation (PowerPoint 2007 (.pptx) 2.6MB Aug25 14)).
An important take-home message from this discussion should be that people tend to exaggerate rare risks (e.g., plane crashes) and downplay more common risks (e.g., car crashes), and that natural risks vary by location. Having an accurate understanding of our risks from natural hazards is important for making decisions in our own lives (e.g., where to live) and for society (e.g., building/maintaining evacuation centers in hurricane-prone areas). After discussing the students' responses to the article, the instructor can initiate a discussion on fatalities from the eight most common weather-related natural hazards, or ask the students to write their reaction to the table below: "What do you find most surprising in this table?"
Weather fatalities (Data Source)
|10-year average (2004-2013)
Risk = Likelihood x Cost
This equation is fundamental to assessing risk. The terms are defined as follows:
Likelihood. For our purposes, likelihood refers to the percent chance of a hazard happening in a specific place over a certain amount of time. Likelihood is an estimate, based on past events.
- Example 1: California has had 8 major (magnitude>7) earthquakes in the last 100 years. That is on average about 12 years between major earthquakes (also called the return period). Therefore, the likelihood of a major earthquake somewhere in the state is 8% each year.
- Example 2: The return period of landslides on Smith Lane is 5 years. The likelihood of a landslide on Smith Lane this year is 20%.×
Cost. Cost refers to the impact of a particular hazard. Cost is both a dollar amount in terms of damages to property and infrastructure, but can also be more difficult to quantify in terms of time/productivity lost, or injuries and deaths.
Risk. Simply stated, risk is likelihood times cost. If the cost is very small or the likelihood is very low, the risk will likely be low.
Question: If your area was hit by 1 hurricane in the last 100 years, and your house is worth $200,000, what is the risk to your house being hit by a hurricane this year?
Answer: 1 hurricane every 100 years means a 1 in 100 (0.01) chance in any given year (or 1% per year). Your home's risk would be: 0.01/year x $200,000 = $2,000/year
Implications: A hurricane insurance policy on your house (if such a thing were available to you) might reasonably cost around $2,000 per year.
Estimating the cost of property and the recurrence intervals of hurricanes is relatively straightforward. However, the risk of being injured or dying in a hurricane is very real to people living in coastal states. On average, nineteen people die as a result of hurricanes each year. You might calculate the likelihood of death in a hurricane (or other natural disaster) as follows:
Likelihood = 19 people per year / 314,000,000 (in 2012)
Cost = dying in a hurricane
Likelihood x Cost = 0.0000061% / year risk of death in a hurricane
Of course, students' personal risk of injury or death by hurricane will be higher in Florida than in North Dakota. You could instruct them to divide the number of deaths per year (for their chosen hazard) in your state by the population of your state, instead of using the national averages.
Learning goals are listed with their associated summative and/or formative assessments.
Learning Goal 1: Define hazard and risk.
Learning Goal 2: List examples of hazards and risks.
Learning Goal 3: Compare hazards and the frequency of their occurrence.
Learning Goal 4: Calculate personal risk.
References and Resources
Kentucky Geologic Survey/University of Kentucky on Earthquake Hazard and Risk: http://www.uky.edu/KGS/geologichazards/risks.htm
Video of Jared Diamond on New Guinean perception of risk: http://www.youtube.com/watch?v=vR2_UWZA7TQ
Hurricane strikes data (Excel 295kB Jul16 12) from the National Hurricane Center
Resources for teaching with data from SERC