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B. Physical Geography and Physical Processes in Canada · Canada's Physical Environment: Landforms, Climate, Hazards and People

Natural Hazards in Canada: Patterns and Trends in Frequency, Severity and Distribution

B1.3 A1.3 A1.4About 75 minutes
Learning goals
  • I can classify natural hazards and describe where in Canada each type is most common.
  • I can describe how the severity of hazards is measured (magnitude, Enhanced Fujita scale, hurricane categories, return periods).
  • I can analyse data to identify trends in the frequency and severity of hazards, and tell a trend from normal year-to-year variation.
  • I can judge whether a source about a disaster is credible.

Words to know

natural hazard
A natural process or event that could harm people, property or the environment, such as a flood or earthquake.
natural disaster
A hazard that actually causes serious harm to a community, beyond what it can cope with on its own.
frequency
How often an event happens.
severity
How strong or damaging an event is.
distribution
Where events happen (their spatial pattern).
return period
The average time between events of a certain size; a "100-year flood" has a 1% chance of happening in any year.
Enhanced Fujita (EF) scale
A scale from EF0 to EF5 that rates tornadoes by the damage they cause (used in Canada since 2013).
atmospheric river
A long, narrow band of very moist air that can bring days of heavy rain, especially to the B.C. coast.
ice jam
A build-up of broken river ice that blocks the flow and can cause sudden flooding upstream.
sensitive (Leda) clay
A marine clay found in parts of the Ottawa and St. Lawrence valleys that can suddenly turn almost liquid and cause landslides.

Every region has its hazards

Ask people in different parts of Canada about the natural events they worry about and you will get very different answers. In Victoria, it might be "the big earthquake". In Winnipeg, "the spring flood". In Calgary, "hail". In Halifax, "hurricanes". In northern Saskatchewan, "wildfire smoke". In Ottawa, "tornadoes and ice storms".

Expectation B1.3 asks you to analyse patterns and trends in the frequency (how often), severity (how strong) and distribution (where) of physical processes and events in Canada. In this lesson you will become a hazard analyst.

Hazards and disasters

A natural hazard is a natural process that could cause harm. It becomes a disaster when it actually seriously harms a community. A powerful earthquake in an empty area is a hazard event; the same earthquake under a city could be a disaster. So disasters depend on both nature and people (you will look at this in the next lesson on risk).

Hazards can be grouped by cause:

  • Geological: earthquakes, tsunamis, volcanic eruptions, landslides and rock falls.
  • Hydrological: floods (from snowmelt, ice jams, heavy rain or storm surge).
  • Meteorological and climatological: tornadoes, hurricanes, hail, ice storms, blizzards, heat waves, drought and wildfires (which are strongly linked to weather).
  • Biological: for example, the mountain pine beetle outbreak that killed huge areas of pine forest in B.C. after a series of mild winters.
West Coastearthquakestsunamislandslidesatmospheric-river floodsCordilleraavalancheslandslideswildfiresfloodsPrairiesdroughthailtornadoesspring floodsblizzardsBoreal, Northwildfiresice-jam floodspermafrost thawcoastal erosionOnt. and Que.tornadoesice stormsfloodsheat wavessensitive-claylandslidesAtlantichurricanes andpost-tropicalstormsstorm surgecoastal erosionWest ← → East. A schematic summary, not a map; each region also has other hazards.
A west-to-east summary of hazards that are especially important in each part of Canada (schematic, not a map). Notice the pattern: geological hazards cluster in the west; storms, ice and heat are more important in the centre and east.

Patterns of distribution: why there?

  • Earthquakes, tsunamis and volcanoes cluster on the west coast, where plates meet (lesson 3).
  • Avalanches and landslides are most common in the mountains, where slopes are steep. In the Ottawa and St. Lawrence valleys, sensitive (Leda) clay left by an ancient sea can suddenly liquefy and slide.
  • Floods are the most frequent natural hazard in Canada and happen in every province and territory. Their causes differ: snowmelt on the flat Red River valley in Manitoba; ice jams on northern rivers in spring; heavy rain in cities with lots of pavement; atmospheric rivers on the B.C. coast, such as the November 2021 floods in the Fraser Valley; and storm surges on the Atlantic coast.
  • Wildfires are most common in the boreal forest and the dry B.C. Interior, where there is lots of fuel and hot, dry summers. Lightning causes about half of Canada's wildfires but a large majority of the area burned, because lightning fires often start in remote places.
  • Tornadoes occur mostly in the southern Prairies, southern Ontario and southern Quebec, where warm, humid air meets cooler, drier air in summer. On September 21, 2018, tornadoes struck the Ottawa–Gatineau area.
  • Hail is especially common in southern Alberta; the area around Calgary is nicknamed "hailstorm alley".
  • Hurricanes and post-tropical storms reach Atlantic Canada in late summer and fall.
  • Ice storms: freezing rain is common in eastern Ontario, Quebec and the Atlantic provinces. The January 1998 ice storm coated the region in ice, toppled power lines and left millions of people without power, some for weeks.

Measuring severity

Each hazard has its own measuring stick:

  • Earthquakes: magnitude (each step ≈ 32 times more energy).
  • Tornadoes: the Enhanced Fujita scale, EF0 (light damage) to EF5 (incredible damage), based on damage to buildings and trees. Canada has used it since 2013.
  • Hurricanes: categories 1 to 5 on the Saffir–Simpson scale, based on sustained wind speed.
  • Wildfire seasons: total area burned (in hectares) and number of fires. The 2023 season burned more than 15 million hectares, the largest area in Canada's recorded history.
  • Floods: water levels and flow, and the return period. A "100-year flood" does not happen once every 100 years like clockwork. It is a flood so large it has a 1% chance of happening in any year. Two can happen in back-to-back years.
1 year1%10 years9.6%30 years26%50 years39.5%100 years63.4%Chance of at least one "100-year flood" over different time spans (1% chance each year).
Even an event with only a 1% chance per year becomes likely over a long time. Over a 30-year mortgage, there is about a 26% chance (roughly 1 in 4) of at least one "100-year flood".
Worked example

Worked example: How likely is a 100-year flood in 30 years?

A house is on land that floods in a "100-year flood". What is the chance of at least one such flood in the 30 years of a mortgage?

  1. Chance of no flood in one year: 1 − 0.01 = 0.99.
  2. Chance of no flood in 30 years in a row: 0.99 × 0.99 × ... (30 times) = 0.99³⁰ ≈ 0.74.
  3. Chance of at least one flood: 1 − 0.74 = 0.26.

About 26%, roughly a 1-in-4 chance. A "100-year" flood is far from rare over a lifetime.

Trends over time: is it really changing?

A trend is a long-term change over time. Hazard data are noisy: one year may be terrible and the next quiet. To find a trend, geographers:

  1. Look at many years of data, not just one or two.
  2. Compare averages of earlier and later periods, or draw a trend line.
  3. Ask why the numbers changed. Rising damage costs may come from more frequent or severe events (for example, linked to a warming climate), from more people and property in hazard zones, from higher costs to rebuild, or from better reporting.

In Canada, the long-term picture includes more area burned by wildfires in many recent years, longer fire seasons, more intense heavy-rainfall events, and rising insured losses from severe weather over recent decades. You will look at the climate change connection in a later lesson.

01002003004005006002016201720182019202020212022202320242025Dashed lines: average 2016–2020 = 176; average 2021–2025 = 376area burned (thousand ha)MADE-UP practice data for an imaginary province, not real statistics.
MADE-UP practice data. The bars jump up and down from year to year, but the average of the last five years (dashed line, right) is much higher than the average of the first five (dashed line, left).
Worked example

Worked example: Finding a trend in noisy data

Use the made-up wildfire data in the bar graph (thousand hectares): 2016: 120, 2017: 300, 2018: 210, 2019: 90, 2020: 160, 2021: 380, 2022: 240, 2023: 520, 2024: 310, 2025: 430. Is there a trend?

  1. Average 2016–2020: (120 + 300 + 210 + 90 + 160) ÷ 5 = 880 ÷ 5 = 176.
  2. Average 2021–2025: (380 + 240 + 520 + 310 + 430) ÷ 5 = 1880 ÷ 5 = 376.
  3. Compare: 376 ÷ 176 ≈ 2.1, so the later average is about twice the earlier one.
  4. Check variability: the data jump around (2019 was low, 2023 very high), so one year alone would mislead. But every year from 2021 on is higher than 2016, 2019 and 2020.
  5. Conclude with care: the data suggest an increasing trend, but ten years is a short record. A geographer would look for longer records and causes (weather, fuel, fire suppression, ignitions).

The average area burned roughly doubled from the first five years to the last five: evidence of an increasing trend, though a longer record would make the conclusion stronger.

🔎 Geographer's toolkit: is this source credible? (A1.3)

During and after a disaster, rumours spread fast on social media. Before you share or trust information, check:

  • Who made it? Government agencies (Environment and Climate Change Canada, Natural Resources Canada, Public Safety Canada, provincial emergency management), local officials, established news outlets and scientists are more reliable than anonymous accounts.
  • When was it posted? Old photos are often re-shared as if they were new.
  • Evidence: does it give data, sources or locations you can check? Does another reliable source confirm it?
  • Purpose and bias: is it trying to inform, sell, frighten or get clicks?

Public Safety Canada's Canadian Disaster Database and Environment and Climate Change Canada's weather alerts are good starting points.

Hands-on activity

Hazard memories vs the record

You need: a family member or neighbour to interview, a computer or tablet, paper.

  1. Ask someone at home: "What is the most serious weather or natural event you remember in Canada? When and where was it? What happened?" Take notes.
  2. Find two reliable sources about the same event (for example, Environment and Climate Change Canada, a provincial government site, a well-known news outlet or the Canadian Disaster Database).
  3. Compare: What details match? What is different (date, size, damage)? Why might memories and records differ?
  4. Classify the event (geological, hydrological, meteorological...) and say where it fits in the patterns from this lesson.

What to look for: a clear comparison table; the student recognizes that memory is valuable for how people experienced an event, while official records are better for exact dates and measurements; both together tell a fuller story. Be sensitive: some people have hard memories of disasters, so let them choose what to share.

Just for fun

A "100-year flood" is not a guest that politely shows up once a century. Rivers have never once checked the calendar.

Your turn

1

What is the difference between a natural hazard and a natural disaster?

2

Which natural hazard is the most frequent in Canada?

3

Why do earthquakes, tsunamis and volcanoes cluster on the west coast?

4

Why are wildfires most common in the boreal forest and the B.C. Interior?

5

What does a "100-year flood" mean?

6

Name the scale used to rate tornadoes in Canada.

7

Give two reasons the cost of disasters could rise even if the number of events stayed the same.

More practice: warm-up

1

Which part of Canada is called "hailstorm alley"?

2

What was unusual about Canada's 2023 wildfire season?

3

What is an atmospheric river?

4

Where do hurricanes or post-tropical storms most often affect Canada?

5

What is frequency?

More practice: on your own

1

What is the chance of at least one 100-year flood in 10 years? Show your work.

2

What is the chance of at least one 50-year flood (2% chance per year) in 2 years?

3

Explain why the Red River valley floods in spring more than many other places.

4

Why do lightning-caused fires burn a large share of the area even though they are only about half of all fires?

5

A social media post shows a photo of a flooded street with the caption "Toronto right now!". How would you check it?

Challenge

1

Using the practice wildfire data, calculate the percent increase from the 2016–2020 average (176) to the 2021–2025 average (376).

2

A town says: "We just had our 100-year flood, so we are safe for the next 99 years." Explain the mistake and what the chance of a 100-year flood next year really is.

3

Insured losses from severe weather in Canada have risen over recent decades. Design a short inquiry to find out how much of that rise is caused by more extreme weather and how much by changes in where and how people live. What data would you need?

Check your understanding

Quiz

1.

Which is the most frequent natural hazard in Canada?

2.

A "100-year flood" has what chance of happening in a given year?

3.

Tornadoes in Canada are rated with the:

4.

Sensitive (Leda) clay landslides are a hazard mainly in:

5.

Which is the best evidence of a long-term trend?

6.

Which source is generally most credible for a weather warning?

7.

In 2023, Canada's wildfires:

For parents and teachers

Big idea: B1.3 asks students to analyse patterns and trends in the frequency, severity and distribution of physical processes and events in Canada. This lesson also practises A1.3 (judging sources) and A1.4 (working with data). The wildfire bar graph uses made-up practice data, clearly labelled.

Common difficulties:

  • The "100-year flood" misunderstanding. Stress "1% chance every year".
  • Calling one bad year a trend. Look for averages over many years.
  • Probability calculations. 1 − 0.99ⁿ needs a calculator; the idea (chance of "none", then subtract from 1) matters more than speed.

Sensitivity: Some families have lived through floods, fires or storms. Let your teen and others share only what they are comfortable sharing. There is no "fun" focus on suffering in this lesson; the joke is only about statistics.

How to help: Sign up together for local weather alerts and look at your municipality's hazard information (for example, a flood map). Ask: "Which hazards matter most here, and why?"