1. Introduce students to the rain gauge.
Ask students to imagine what it would look like if all the water that fell during a rainstorm stayed where it fell and did not soak into the ground or flow into a river. What depth of water would cover the ground? Would it cover your shoes? Explain that the rain gauge measures the amount of water that falls during a rainstorm in inches so that we know how much water fell to the ground.
2. Demonstrate how to read a rain gauge.
Explain that water is funneled from a wider area into a narrower area in the gauge, so the measurement scale on the inner tube is enlarged and an inch of rainfall looks much larger. You can demonstrate this by pouring less than one inch of water into the outer cylinder, measuring the depth with a ruler, and then pouring the water into the inner cylinder, which should measure the same amount even though it will appear much deeper.
Ask students to hypothesize what would happen if there were more than one inch of rainfall. Pour water into the gauge so that it overflows the inner tube. Show students how to measure the water in the inner tube and then the water that spilled over into the outer tube and add the numbers. Play the two CoCoRaHS video segments.
3. Read the rain gauge story and measure the rainfall day-by-day.
Select eight students to each read one chapter of the story to the class. (With younger students, plan to read the story to students.) After each student reads a chapter, fill the rain gauge with the water you premeasured for that day of the story and have one or two students read the gauge. After the students have measured the water for that day, empty the rain gauge and then read the next chapter.
For days during the story when there was more than an inch of rainfall, students will need to follow these steps:
- Measure the amount of water that is in the inner tube and record the number.
- Remove and empty the inner tube.
- Place the funnel on the top of the inner tube and pour the water from the outer tube into the inner tube.
- Measure the remaining water in the inner tube and record the number.
- If there is still more water in the outer tube, repeat steps 2‐4 until there is no more water to measure.
- Add all the numbers together to get the rainfall total for that day.
Classroom management: Have all students record the data while one or two students are reading the gauge. Invite a new pair of students to read the gauge for each day of the story. For Thursday’s rain gauge reading (8.43 inches of water), numerous students can get involved with measuring because the inner tube will need to be measured and emptied at least nine times. Students will have many numbers to add to find that day’s total rainfall.
4. Graphing the data
Below are the rain gauge measurements, made by Bill Schmoker at Centennial Middle School in Boulder, Colorado, during the extreme rainfall event in September 2013. To the right of each measurement is the amount rounded to the closest half‐inch. You may wish to have students explore the rounded data depending on math skills. Have students construct a bar graph with inches on the y-axis (vertical) and date on the x-axis (horizontal).
For a more simple graph of the data, have students fill seven empty soda bottles with the number of inches of water that were measured, place in order of the date, and take a photo or draw a picture.
Rainfall data collected by Mr. Schmoker at Centenial Middle School in Boulder, Colorado during the extreme rainfall event in 2013.
Credit: CoCoRaHS measurements, UCAR data table