A. Physical Patterns in a Changing World · Physical Patterns in a Changing World

Reading and Making Climate Graphs

A3.8 A2.4About 50 minutes

Learning goals

I can read a climate graph to find temperature range, total precipitation and the wettest and driest months.
I can construct a climate graph from data.
I can use a climate graph to describe and classify a place's climate.

Words to know

climate graph
A graph that shows a place's average monthly temperature (as a line) and average monthly precipitation (as bars) on one set of axes.

temperature range
The warmest month's average temperature minus the coldest month's average.

total annual precipitation
All twelve months of average precipitation added together, in millimetres (mm).

climate normal
An average of weather data for a place, usually over 30 years, published by weather services.

Northern Hemisphere
The half of Earth north of the equator.

Southern Hemisphere
The half of Earth south of the equator, where the seasons are opposite to Canada's.

One picture, a whole year

A climate graph shows a whole year of a place's climate in one picture. Geographers use them to compare places around the world quickly. Once you can read one, you can tell if a place is hot or cold, wet or dry, and even which hemisphere it is in!

The data in this lesson are sample data, rounded and made up for practice, but shaped like real climates. You can find real data for Canadian places in Environment and Climate Change Canada's climate normals.

A white louvered instrument shelter on legs, a metal rain gauge and a pole with a wind vane and cup anemometer stand in a grassy field. — A weather station. The shelter holds the thermometer, the gauge collects precipitation, and the cups measure wind. Daily readings averaged over 30 years become a climate graph. AI-generated image

How a climate graph works

Months go along the bottom (J for January to D for December).
Temperature is a line graph, read on the left axis in °C.
Precipitation is a bar graph, read on the right axis in millimetres (mm).

Four things to find:

Warmest and coldest months (highest and lowest points on the line).
Temperature range = warmest − coldest.
Total annual precipitation = add all 12 bars.
Wettest and driest months (tallest and shortest bars).

City A (sample data): the temperature line goes from about −6 °C in January to 22 °C in July. The precipitation bars are fairly even, 55 to 85 mm each month.

City A	J	F	M	A	M	J	J	A	S	O	N	D
Temp. (°C)	-6	-5	0	7	13	19	22	21	17	10	4	-3
Precip. (mm)	60	55	60	70	80	80	85	80	85	70	80	65

City A sample data.

Worked example

Let's read City A's climate graph

Use the graph and table for City A. Find the warmest and coldest months, the temperature range, the total precipitation and the wettest months. Then classify the climate.

Warmest: July, 22 °C. Coldest: January, −6 °C.
Range: 22 − (−6) = 22 + 6 = 28 °C. Subtracting a negative is the same as adding.
Total precipitation: 60 + 55 + 60 + 70 + 80 + 80 + 85 + 80 + 85 + 70 + 80 + 65 = 870 mm.
Wettest: July and September (85 mm). Driest: February (55 mm). Precipitation is spread fairly evenly through the year.
Classify: warm summers, cold winters below 0 °C, a large range, and moderate precipitation all year → continental. Coldest in January means Northern Hemisphere.

City A has a continental climate (range 28 °C, 870 mm a year), like many places in southern Ontario.

City B (sample data): the temperature line stays flat at 27 to 28 °C all year. The precipitation bars are tall in every month, from 130 to 290 mm.

City B	J	F	M	A	M	J	J	A	S	O	N	D
Temp. (°C)	27	27	28	28	28	28	28	28	27	27	27	27
Precip. (mm)	240	160	190	180	170	130	150	150	170	190	250	290

City B sample data.

Worked example

Let's compare City A and City B

Compare City B's climate with City A's.

City B range: 28 − 27 = 1 °C. Almost no change all year. City A's range is 28 °C.
City B total: 240 + 160 + 190 + 180 + 170 + 130 + 150 + 150 + 170 + 190 + 250 + 290 = 2 270 mm, more than 2.5 times City A's 870 mm.
City B wettest: December (290 mm). Driest: June (130 mm), which is still wetter than any month in City A.
Classify City B: hot all year with heavy rain every month → tropical wet (rainforest).

City B is tropical wet: hot and very rainy all year, with a tiny temperature range. City A is continental, with big seasonal changes.

Worked example

Let's construct a climate graph

Make a climate graph for a place using a table of 12 monthly temperatures and precipitation values.

Draw the axes. Months along the bottom, evenly spaced. Temperature scale on the left, precipitation scale on the right. Choose scales that fit the highest and lowest values (include negative temperatures if needed).
Draw the bars first. For each month, draw a bar up to the precipitation value, using the right axis. Colour them (often blue).
Plot the temperature. Put a dot above the middle of each month at the temperature, using the left axis. Join the dots with a line (often red).
Label everything: title with the place name, both axis titles with units (°C and mm), and a legend.
Check: pick two months and make sure the dot and bar match the table.

A complete climate graph has a title, two labelled axes with units, bars for precipitation, a line for temperature, and 12 evenly spaced months.

Just for fun

Why was the climate graph so popular at parties?

It had great bars and a nice line.

Hands-on activity

Make your own town's climate graph

You need: graph paper (or plain paper and a ruler), a pencil, coloured pencils, and a device with a grown-up's help.

Search for "Canadian climate normals" from Environment and Climate Change Canada and find the nearest station to your home. (If you can't get online, use the City A table.)
Copy the average daily temperature and total precipitation for each month into a table. Round to whole numbers.
Construct the climate graph using the five steps in the example.
Find the range, the total precipitation, and the wettest and driest months.
Write two sentences describing your climate and classify it.

What to look for: evenly spaced months, two labelled scales with units, bars and a line, a title, and correct calculations.

Your turn

On a climate graph, which is shown as a line and which as bars?

City C (sample data): warmest month 32 °C, coldest month 14 °C. What is the temperature range?

City D (sample data): warmest 9 °C, coldest −28 °C. What is the range?

City C's monthly precipitation (sample data) is 3, 2, 2, 1, 1, 0, 0, 0, 0, 1, 2, 3 mm. What is the total? What climate is this?

City D's precipitation (sample data) is 10, 10, 12, 13, 15, 20, 35, 40, 30, 25, 15, 12 mm. Find the total and the wettest month.

City D's coldest month is −28 °C and its warmest is only 9 °C. Classify its climate.

Why do you put temperature dots in the middle of each month's space?

More practice: warm-up

What unit is used for precipitation on a climate graph?

What unit is used for temperature?

How do you find total annual precipitation?

Warmest 20 °C, coldest 4 °C. What is the range?

On which axis do you read precipitation in this lesson's graphs?

More practice: on your own

City E (sample data) temperatures: J 24, F 24, M 22, A 19, M 16, J 13, J 12, A 13, S 15, O 17, N 20, D 22 °C. What is the warmest month, the coldest month and the range?

City E is warmest in January and coldest in July. Which hemisphere is it in? Explain.

City E's precipitation (sample data): 100, 110, 120, 120, 110, 130, 90, 80, 70, 75, 85, 80 mm. Find the total.

Classify City E's climate. Give reasons.

A student draws a climate graph but uses different-sized spaces for some months. Why is that a problem?

Challenge

Rank Cities A, B, C, D and E from wettest to driest by total annual precipitation.

City D gets only 237 mm a year, yet it is not a hot desert. Explain why it can still have snow on the ground for much of the year.

You are given two unlabelled climate graphs: one has a temperature line that is almost flat and high; the other has a line that dips below 0 °C in the middle of the year. What can you infer about where each place is?

Check your understanding

Quiz

On a climate graph, precipitation is usually shown as...

Warmest month 22 °C, coldest −6 °C. The temperature range is...

A place has 27–28 °C every month and over 2 000 mm of rain a year. Its climate is...

A place's warmest month is January. It is most likely in the...

To find total annual precipitation, you...

A place gets 15 mm of precipitation in a whole year and is hot. It is a...

For parents and teachers

Big idea: Expectation A3.8 asks students to analyse and construct climate graphs to gather information on and illustrate climate patterns for specific locations. A2.4 asks them to interpret data using various tools, such as graphs. The cities in this lesson are sample data, not real places, so you can focus on the skill.

How to help: Look up your town's climate normals together (Environment and Climate Change Canada) and build a graph. Ask, "What's the range? Which month is wettest? How is this different from City B?"

Common difficulties:

Ranges with negative numbers: 22 − (−6) is 28, not 16. Use a thermometer-style number line to count the degrees.
Mixing the two axes: remind your child that the line uses the °C scale and the bars use the mm scale.
Forgetting units and titles.
Forgetting that seasons are flipped in the Southern Hemisphere.