# Make a Rain Gauge to Study Precipitation

## Summary

3rd
Group Size
2-3 students
Active Time
90 minutes
Total Time
90 minutes
Key Concepts
Precipitation, weather
Credits
Sabine De Brabandere, PhD, Science Buddies

## Overview

Rainstorms can be powerful! Can you guess how much water poured down during the last rainstorm you experienced? Do you know if a brief downpour yields more or less water compared to a daylong drizzle? In this hands-on weather lesson, students design, build and use their own rain gauge to get answers to all of these questions.

## Learning Objectives

• Can use the word precipitation correctly
• Can draw, construct, and read a rain gauge
• Knows and understands the units of precipitation
• Can give a rough estimate of how much rain (in inches or mm) a rainy day delivers.

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
• 3-ESS2-1. Represent data in tables and graphical displays to describe typical weather conditions expected during a particular season.
• 3-ESS2-2. Obtain and combine information to describe climates in different regions of the world.
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

 Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Science & Engineering Practices Developing and Using Models. Develop a diagram or simple physical prototype to convey a proposed object, tool, or process. Analyzing Data. Compare and contrast data collected by different groups in order to discuss similarities and differences in their findings. Use data to evaluate and refine design solutions. Disciplinary Core Ideas ESS2.D: Weather and Climate. Scientists record patterns of the weather across different times and areas so that they can make predictions about what kind of weather might happen next. Crosscutting Concepts Scale, Proportion and Quantity. Students recognize natural objects and observable phenomena exist from the very small to the immensely large. They use standard units to measure and describe physical quantities such as weight, time, temperature, and volume.

## Materials

For the class:

• Containers to make the body of a rain gauge. Good examples are empty, clean plastic bottles, milk containers, jars, tall food containers and cans. Select containers that have straight edges. A curved bottom is fine. They need to be waterproof; transparent containers are preferred.
• Materials and tools to finish the rain gauge. Examples are scissors, permanent markers, rulers, tape, paperclips, clay, water, gravel, wooden panel and glue.
• Water
• A few one gallon or larger containers (e.g. one-gallon milk or water containers) to make rain cans, a push pin and one opaque plastic bag to cover the container.
• Graph paper with a 1 cm squared grid like this one (at least 2 sheets)
• Optional: a few funnels that fit on the smaller containers.
• Optional: a hose with spray nozzle that allows different spray patterns.
• Outside area that can get wet

## Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

Rain is one form of precipitation, together with snow, hail and sleet. Precipitation can be defined as any form of water falling from the sky onto earth's surface, or the amount of water falling on a certain area in a specific amount of time. Measuring the amount of precipitation is the focus of this lesson.

Precipitation is essential to life on earth. It refills our lakes, rivers and oceans; it seeps into the ground where it nourishes plants, fills aquifers (underground water reservoirs) and supplies water for springs. Too little precipitation, and life dies out, too much and you have devastating floods or landslides (Figure 1).

Figure 1. Too little or too much precipitation can lead to drought (top) and flooding (bottom).

Meteorologists—scientists who study the weather and climate—keep a close eye on precipitation. They study short and long-term patterns in order to make predictions and warn people of upcoming dangerous situations such as flash floods or flooding, droughts, etc.

Precipitation is measured as the height of water collected in a container with straight edges that rise up at right angles with the bottom. It is expressed in inches or millimeters (mm). Figure 2 illustrates that precipitation measurements are independent of the surface covered by the collecting container. Although containers covering a larger surface collect more water, the height of the collected water is the same as that collected in a smaller container.

Figure 2. Two containers used to measure precipitation. Although the surface the containers cover is different, they measure the same height of rain.

For most regions, precipitation comes mainly in the form of rain. It is measured in a rain gauge (or udometer). Rain gauges are placed outside in an open area, so nothing obstructs the collection of precipitation. The most straightforward rain gauge is a transparent cylinder with an open top as shown in Figure 3 on the left. The water level in the gauge shows the precipitation in that area since the gauge was last emptied. Markings measured from the bottom of the cylinder make it easy to read the water level.

Figure 3. Straight rain gauge (left) and funnel rain gauge (right).

A slightly more complicated design uses a funnel that guides water into a transparent cylinder (Figure 3, right). This design works better in areas where there is little rain, and often also reduces evaporation of collected water. The water level in the cylinder is still an indication of the precipitation but it is not the precipitation in inches or millimeters. You have to multiply the measured water level by the ratio of the funnel's diameter to the cylinder's diameter. The formula below can explain.

Other rain gauges have buckets that tip over when full. The number of tipped buckets is a measure of precipitation. Still others measure the mass of rain collected or use acoustic or optical measurements. In this lesson, students will design, make and test their own rain gauges in small groups.

Rain is classified according to the amount of water falling per hour. The table below lists the classification. One inch is 25.4 mm; rain of 1 inch/hour is a heavy downpour.

Type In millimeters per hour
Light 2 - 4
Moderate 5 - 9
Heavy 10 - 49
Violent More than 50

The amount of water collected in a rain gauge might seem small, a few inches at most on a typical rainy day, but the volume of water quickly adds up. A roof that measures 40 by 70 feet (12 by 21 meters) collects about 1.74 gallons or 6.6 liters of water if your rain gauge measures 1 inch of precipitation; a square mile (2.6 km²) collects 17.38 million gallons of water (65.78 million liters). Using this number allows you to calculate the volume of water your city, village or school grounds would receive for 1 inch of precipitation: multiply the 17.38 million gallons by the area covered (expressed in square miles).

Where does all that water go? That depends on the rate at which the water falls, the geography and ground-cover of the area and the temperature. In a downpour, a lot of the water becomes surface runoff or water flowing over the land into creeks, streams, rivers and lakes. Urban areas have a much higher percentage of runoff. The high concentration of impermeable pavements and roofs, and the storm-sewer system account for that. The higher runoff drastically increases the chances of flooding. Water that falls at a slower rate has more time to infiltrate the ground and feed aquifers (underground water reservoirs) and vegetation. Water left in puddles or in wet surfaces evaporates. In the US, an average of about 70 percent of the precipitation returns to the atmosphere by evaporation from land and other small water surfaces, and by vegetation breathing out water vapor (referred to as transpiration). This water vapor feeds cloud formation, which leads to precipitation. This lesson briefly touches on what happens to the water that falls from the sky but leaves the water cycle for another lesson.

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