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

What Shapes Canada's Climate? Climate Controls and Climatic Processes

B1.2 B1.1 B1.4 A1.4About 75 minutes

Learning goals

I can explain how latitude, ocean currents, winds and air masses, elevation, relief and nearness to water shape climates across Canada.
I can explain the three kinds of precipitation (relief, convectional and frontal) and why a rain shadow forms.
I can calculate temperature range and use it to tell a maritime climate from a continental one.
I can describe how climatic processes such as freeze–thaw, permafrost and wind continue to shape Canada's landscape.

Words to know

climate
The average weather conditions of a place over a long time (usually 30 years).

climatic process
A process of the atmosphere that shapes the land, such as freeze–thaw weathering, wind erosion or the formation of permafrost.

air mass
A huge body of air with similar temperature and moisture throughout, taking on the character of the area it formed over.

maritime climate
A climate influenced by a large body of water: mild winters, cool summers, small temperature range, more precipitation.

continental climate
A climate far from the moderating effect of the ocean: cold winters, warm or hot summers, large temperature range, less precipitation.

temperature range
The difference between the warmest and coldest monthly mean temperatures.

lapse rate
The rate at which air temperature drops with height; in still air about 6.5 °C for every 1000 m.

relief (orographic) precipitation
Precipitation caused when moist air is forced to rise over mountains and cools.

rain shadow
A dry area on the leeward (downwind) side of mountains.

freeze–thaw weathering
Water seeps into cracks, freezes and expands, and slowly breaks rock apart.

permafrost
Ground that stays frozen (at or below 0 °C) for at least two years in a row.

Same latitude, different worlds

Vancouver and Winnipeg are at about the same latitude, yet in January Vancouver often has rain and green grass, while Winnipeg has snow and temperatures well below −20 °C on some days. In July, Winnipeg is often the warmer of the two. Why such different climates?

In Grade 7 you learned the six climate factors with the word LOWERN and practised climate graphs. In Grade 9 you will use these climate controls to explain the climate patterns of Canada, calculate and compare data, and see how climate itself shapes the land.

LOWERN applied to Canada

L: Latitude. Canada stretches over 40° of latitude. The farther north, the lower the sun's angle and the shorter the summer days, so average temperatures drop going north. Iqaluit's warmest month, July, averages only about 8 °C.
O: Ocean currents. The warm North Pacific (Alaska) Current keeps B.C.'s coast mild. The cold Labrador Current chills Newfoundland and Labrador; where it meets the warm Gulf Stream near the Grand Banks, warm moist air is cooled over cold water, creating frequent fog.
W: Winds and air masses. Most of southern Canada lies in the prevailing westerlies, so weather systems usually move west to east. Air masses bring their source region's character (see the diagram).
E: Elevation. Temperature falls about 6.5 °C for every 1000 m you climb (the lapse rate). Banff (about 1400 m) is cooler than Calgary (about 1050 m), and both are cooler than places at sea level at the same latitude.
R: Relief. Mountains block air and force it to rise. The western slopes of the Coast Mountains are among the wettest places in Canada, while valleys to the east, such as the Okanagan, are much drier: a rain shadow.
N: Nearness to water. Water heats up and cools down much more slowly than land. Places near oceans have maritime climates (mild winters, cool summers, small temperature range). Places far inland have continental climates (cold winters, warm summers, large range). The Great Lakes also moderate nearby areas and create lake-effect snow in places such as the snowbelts east of Lake Huron and Georgian Bay.

The main air masses that affect Canada (schematic, not to scale). Arrows show the general direction each tends to move in. The weather you get depends on which air mass is over you, and fronts form where two meet.

Three ways to make precipitation

All precipitation happens when moist air rises and cools, so water vapour condenses. What makes the air rise?

Relief (orographic) precipitation: wind pushes air up a mountain slope. Common on the B.C. coast. On the far (leeward) side, the air sinks and warms, so it is dry: a rain shadow. In southern Alberta, warm, dry, downslope chinook winds can quickly melt snow in winter.
Convectional precipitation: the sun heats the ground, warm air rises in bubbles and forms tall clouds. This produces summer thunderstorms, common on the Prairies and in southern Ontario.
Frontal (cyclonic) precipitation: a warm air mass meets a cold one. The lighter warm air is pushed up over the denser cold air. This makes most of the rain and snow in central and eastern Canada, especially in spring, fall and winter.

Relief precipitation and a rain shadow (schematic, not to scale). Moist Pacific air drops rain and snow as it climbs the windward slope; the air that sinks down the leeward side is drier and warmer.

🔎 Geographer's toolkit: comparing climate data

Environment and Climate Change Canada publishes climate normals, 30-year averages, for hundreds of places. Two quick calculations tell you a lot:

Temperature range = warmest month mean − coldest month mean. A small range (under about 20 °C) suggests a maritime climate; a large range (over about 30 °C) suggests a continental one.
Total annual precipitation: maritime places are usually wetter; continental interiors are drier.

The chart below shows approximate January and July means for six Canadian places (rounded 30-year averages).

January and July mean temperatures for six places (approximate, rounded). Vancouver's small range shows a maritime climate; Winnipeg's large range shows a continental one; Iqaluit is coldest because of its high latitude.

Place	January mean (°C)	July mean (°C)	Range (°C)	Annual precipitation (mm)
Vancouver, B.C.	about 4	about 18	about 14	about 1200
Winnipeg, Man.	about −16	about 20	about 36	about 520
Halifax, N.S.	about −6	about 19	about 25	about 1400
Toronto, Ont.	about −5.5	about 22	about 27.5	about 790
Calgary, Alta.	about −7.5	about 17	about 24.5	about 450
Iqaluit, Nun.	about −26	about 8	about 34	about 360

Approximate climate normals (rounded 1991–2020 averages for each city's airport station, from Environment and Climate Change Canada). Check the current normals online for exact values.

Worked example

Worked example: Maritime or continental?

Use the table to compare Vancouver and Winnipeg. Calculate each temperature range and explain the difference using LOWERN.

Vancouver: 18 − 4 = 14 °C range.
Winnipeg: 20 − (−16) = 20 + 16 = 36 °C range. (Subtracting a negative means adding.)
Vancouver's range is small and its precipitation is high: maritime. Winnipeg's range is large and its precipitation is low: continental.
Explain: Vancouver is beside the Pacific (N), with the mild North Pacific Current offshore (O) and westerly winds blowing in from the ocean (W). Winnipeg is in the middle of the continent, far from any ocean, and Arctic air masses can sweep down over the flat plains in winter.
Bonus: Winnipeg is also in the rain shadow of the western mountains, so most Pacific moisture has already fallen (R).

Vancouver has a maritime climate (range 14 °C); Winnipeg has a continental climate (range 36 °C). The key controls are nearness to water, ocean currents, winds and relief.

Worked example

Worked example: Using the lapse rate

On a summer afternoon it is 24 °C in Jasper, Alberta (about 1060 m above sea level). Estimate the temperature on a nearby peak at 3060 m, using a lapse rate of 6.5 °C per 1000 m.

Height difference: 3060 − 1060 = 2000 m.
Temperature drop: 2000 ÷ 1000 = 2; 2 × 6.5 = 13 °C.
Temperature at the peak: 24 − 13 = 11 °C.

About 11 °C on the peak. This is why mountain tops can hold snow all summer and why vegetation changes as you climb.

Climate shapes the land too

Climate is not just about what to wear. Climatic processes keep shaping Canada's landscape:

Freeze–thaw weathering: water seeps into cracks in rock, freezes, expands by about 9%, and pries the rock apart. Repeated over many freeze–thaw cycles, it breaks rock into pieces. It is strong in places with many cycles around 0 °C each year, such as the mountains and much of southern Canada, where it also creates potholes in roads.
Permafrost: in the far north, the ground stays frozen year-round below a thin active layer that thaws each summer. Permafrost underlies a large part of Canada's land (roughly 40 to 50 percent). Freezing and thawing of the active layer creates patterned ground and mounds such as pingos (ice-cored hills found in the Mackenzie Delta area near Tuktoyaktuk).
Wind: in dry areas with little plant cover, wind erodes and moves soil. During the drought of the 1930s, wind blew away topsoil across parts of the Prairies.
Soils and vegetation: climate controls how fast soils form and what plants grow, which you will see in the lesson on ecozones.

Hands-on activity

Land vs water: the heat race

You need: two identical cups or small bowls, water, dry sand or garden soil, a kitchen thermometer (or a digital meat thermometer), a sunny windowsill, a timer, paper for a table.

Fill one cup with water and one with sand or soil, both at room temperature. Measure and record the starting temperature of each.
Put both in the same sunny spot. Measure each one every 10 minutes for 30 minutes.
Move both into the shade (or a cool room). Measure every 10 minutes for 30 more minutes.
Make a line graph with two lines (time across, temperature up).
Explain: Which heated faster? Which cooled faster? How does this help explain why Vancouver's winter is milder than Winnipeg's?

What to look for: the sand or soil heats up and cools down faster; the water changes temperature more slowly. That is why oceans and large lakes keep nearby places milder in winter and cooler in summer. Grown-up note: if you use a lamp instead of the sun, keep it away from paper and cloth and do not touch the hot bulb.

Just for fun

How do you know you live in a continental climate?

You need a parka and sunscreen in the same week, and sometimes on the same day.

Your turn

What does each letter of LOWERN stand for?

Why is the Grand Banks area often foggy?

Calculate the temperature range for Halifax (January −6 °C, July 19 °C). Is this closer to maritime or continental?

Explain why the Okanagan Valley in B.C. is much drier than Vancouver.

Which type of precipitation causes most summer thunderstorms on the Prairies?

Explain freeze–thaw weathering in three steps.

Why does the temperature drop as you climb a mountain?

More practice: warm-up

In which direction do most weather systems move across southern Canada?

What is permafrost?

Name the cold ocean current off Newfoundland and Labrador.

Which climate type has a small temperature range: maritime or continental?

What is a rain shadow?

More practice: on your own

Calculate the range for Iqaluit (January −26 °C, July 8 °C). Why is it so cold even in July?

The temperature at the base of a ski hill (800 m) is −2 °C. Estimate the temperature at the top (1800 m).

Explain why the snowbelt east of Lake Huron gets so much snow.

Toronto's annual precipitation (about 790 mm) is less than Halifax's (about 1400 mm). Give two reasons.

How can climate help explain why the Prairies lost so much soil in the 1930s?

Challenge

Calgary (about 1050 m) and Winnipeg (about 240 m) are both continental, but Calgary's January mean (about −7.5 °C) is much milder than Winnipeg's (about −16 °C), even though Calgary is higher. Use at least two climate controls to explain this.

A mountain town at 500 m has a mean July temperature of 18 °C. Above what elevation would you expect the July mean to be below 0 °C (ignoring other factors)?

Predict how warmer winters with more temperature swings around 0 °C could affect freeze–thaw weathering and roads in southern Ontario.

Check your understanding

Quiz

Which pair of climate controls best explains why Vancouver's winters are milder than Winnipeg's?

A place with a temperature range of 36 °C most likely has:

Rain caused by air forced up over mountains is:

Using 6.5 °C per 1000 m, if it is 15 °C at 0 m, about what is it at 2000 m?

Fog on the Grand Banks forms mainly because:

Which climatic process breaks rock as water in cracks freezes and expands?

For parents and teachers

Big idea: This lesson covers the climatic part of B1.2 (climatic processes formed and continue to shape Canada's landscape) and links to B1.1 (how climate differs among regions) and B1.4 (air masses and ocean currents are global systems; the next lesson goes further). It also practises A1.4: working with climate data.

Common difficulties:

Negative numbers in ranges. 20 − (−16) = 36, not 4. Have your teen picture a thermometer: from −16 up to 0 is 16, then up to 20 is 20 more.
Thinking latitude explains everything. Vancouver and Winnipeg show why other controls matter.
Mixing up windward and leeward. Windward = the side the wind hits (wet); leeward = the sheltered side (dry).

How to help: Look up your town's climate normals on the Environment and Climate Change Canada website and compare them with a relative's town elsewhere in Canada. Notice the daily weather: "Which way is the wind coming from? What air mass might that be?"