1. A Climagraph with a Better Design

Review with students the basics of a climagraph (Lesson 1, Climate Science - A climagraph is a graphic representation of the three major elements of climate: temperature, precipitation and seasons for a specific location). In this lesson, a climagraph with a better design is used to show more information. Show Climagraph of Detroit transparency (or slides 2-4).

• Which month has the most precipitation? (June) How much? (almost 4 inches)

• What is the lowest average monthly temperature experienced by Detroiters in 2010? (25o F.)

• How many inches of rain does Detroit get in a typical September? (3)

• What is the average temperature in Detroit in May? (60°) in July? (70°)

Then show Climagraph of Detroit, Redesigned transparency (or slide 5). The second climagraph is redesigned and simplified, but it can actually tell us more useful information about the climate of Detroit. It has only three temperature lines, but each one is very significant for human activities.

Slide 6

• How many months have average temperatures clearly above room temperature? (3)

• How many months have average temperatures clearly above 50 degrees Fahrenheit? (5)

Note: If a month has an average temperature of 50 degrees, it is likely to have at least one frost. As a result, a count of the months with temperatures above 50 gives you an estimate of the length of the growing season in a place. Corn requires a growing season of 5 months. Cotton needs at least 7 months. The graph tells you that people in southern Michigan can grow corn, but not cotton.

2. Water Balance

Show Climagraph of Detroit, Redesigned transparency again (or slide 7). Notice how the scales for temperature and precipitation overlap on this climagraph. These scales are carefully matched. This allows the climagraph to provide an estimate of water balance in each month.

Water balance is an accounting of all water volumes that enter and leave a place over a specified period of time. Water balance is usually calculated monthly - each month is either in balance or in surplus or deficit. If the precipitation bar for a given month extends clearly above the temperature line, that month has more water than plants need. This is called a moisture surplus.

Surplus water fills the soil. Additional water runs off the surface (or seeps through the soil) to make rivers and lakes. (Slide 8)

If a bar for a month does not reach up to the temperature line that month has a water deficit (shortage). Plants can survive a short water deficit by using water in the soil. A long deficit, however, can reduce crop yields. That’s called a drought. (Slide 9)

Slide 10:

• How many months have a water surplus in Detroit? (6)

• How many months have a water deficit in Detroit? (4)

• What is the water deficit in August? (1 inch)

What kind of impacts would occur if the water balance for some months is changed? (Slide 11)

Assign each student How Climate Change Can Alter the Water Balance student activity. Check understanding with Slides 12-13.

3. Water Levels in the Great Lakes (Slide 14 or Level of Lake Michigan transparency)

This graph shows the level of Lake Michigan for the last 50 years. Water level responds to changes in water surplus or water deficit. Surplus water makes rivers that flow into the lake. That raises the level of the lake. Higher water levels can push more water out of the Great Lakes through the St. Lawrence River. At the same time water is always evaporating from the lake. Evaporation depends on temperature – more water evaporates when the weather is hot.

4. The level of water in a lake depends on the balance between four things: (Slide 15)

1) How much rain and snow fall directly into the lake

2) How much water evaporates from the surface of the lake

3) How much water comes into the lake from rivers and groundwater springs

4) How much water goes out of the lake in rivers or groundwater seepage. 

Ask students to explain each of these factors, and what they have learned about how potential climate changes can affect each. Possible answers:

1) Rainfall is expected to increase in the fall, winter and spring, and decrease in the summer; lake levels will respond accordingly.

2) Rise in temperatures might increase evaporation from the surface of the lake possibly resulting in more rain and snowfall.

3) This will also depend on rain and snowfall more rain will increase both rivers and groundwater.

4) Months with water deficits might use up more groundwater to satisfy thirsty plants; higher lake levels will increase the water going out of the Great Lakes.

Assign Water Level in Lake Michigan student activity. Option: Assign a five paragraph essay to advise the owners of a lake house next to Lake Michigan. The essay should explain what specific action the owner should take, based on the results of some specific things the essay recommends that he/she measures (like the elevation of the house or its distance from the shore).

5. Tying it all together.

As a conclusion to the discussion of the impact of climate change in the Great Lakes, assign Climate Change and the Great Lakes student resource, and Effects of Climate Change on the Great Lakes student activity.

Discuss student answers to emphasize the complications of cause and effects of climate change. (Slides 15-16)

Note to Students: If you found this hard, you are not alone. Trying to decide what is cause and what is effect is a difficult job. It is even more complicated when the causes and effects are different in different places or different seasons. For example, warmer water may cause fish to die in a shallow bay in Lake Erie (the shallowest and warmest lake). At the same time, warmer water may stimulate more plant growth and more fish populations in a deep part of Lake Superior (the deepest and coldest lake). For this reason, people in Michigan must be very careful when they read scientific studies done in other lakes. The results might not apply to the parts of the Great Lakes that touch Michigan.