Lab 4: When Precipitation Patterns Change

The lab activity described here was created by Betsy Youngman of Phoenix Country Day School and LuAnn Dahlman and Sarah Hill of TERC for the EarthLabs project.

Summary and Learning Objectives

In this activity students develop a practical understanding of the causes and symptoms of drought. They read background articles and prepare a physical model to illustrate the role that soil moisture plays in preventing or promoting drought. Students use Google Earth to examine precipitation and streamflow data and use them to predict locations that are experiencing drought. They check their predictions by comparing them to a drought monitor map. In the final section, students examine and interpret the current map of the Palmer Drought Severity Index.

After completing this investigation, students will be able to:

  • Interpret climographs
  • Write a practical definition of drought
  • Use Google Earth to visualize precipitation and streamflow data
  • Correlate current streamflow and drought datasets
  • Interpret drought index images to read moisture conditions

Open the Student Lab »

Context for Use

This lab defines drought and how it is measured and tracked. Students build on and use the knowledge they gained about water availability, watersheds, and climate (Labs 1, 2, and 3, respectively) to understand that drought occurs when precipitation falls below normal in a watershed, leading to lower soil moisture, higher temperatures and eventually to reduced streamflow.

Time Required

  • Part A: 50 minutes, could be assigned as homework
  • Part B: 30 minutes for hands-on activity, 50 minutes for Google Earth exploration
  • Part C: 30 minutes, could be assigned as homework

Activity Overview and Teaching Materials

Part A of the activity introduces students to the concept of deviation from "normal" precipitation patterns. Students view and interpret and accumulated precipitation graphs, generated from this page at Southern Regional Climate Center. Students read articles to learn how drought is defined, what the indicators of drought are, and how drought is tracked.

Part B begins with a hands-on activity that demonstrates the role of soil moisture in preventing or promoting drought. The activity could also be performed as a demonstration: it requires 2 small containers, plastic wrap, potting soil, and water. Students also use Google Earth to explore images that show actual precipitation and departure from normal precipitation and streamflow levels. They make predictions about areas of drought and check themselves by examining a Drought Monitor map image.

In Part C, students read articles and examine drought index maps to gain practice interpreting drought index maps and to develop a fuller understanding of the concept of drought monitoring.

Printable Materials

You may want to provide a hard copy of the activity sheet on which students can record their answers:

, . Suggested Answers: , . Educators are encouraged to customize the questions and add new ones to meet specific learning goals in your location.

Teaching Notes and Tips

If students have access to Internet-connected computers outside of class, Parts A and C can be assigned as homework assignments. The hands-on lab activity in Part B will take most of one class period to set up and record observations. Teachers may decide to do this lab as a demonstration.

Students need basic skills for navigating and controlling which layers are visible within Google Earth. The lab also involves downloading new data sets. If limited bandwidth is an issue, teachers may decide to complete this step ahead of time in order to make sure that the computer lab time is used efficiently. Another option is to have one student in each team set up the hands-on activity while the other downloads the data sets for the Google Earth portion.


To assess student understanding, you may decide to collect and grade student answers to the Stop and Think Questions. Another option is to have students capture and describe screen shots of their work in Google Earth.

State and National Science Teaching Standards

Additional Resources

Background Information

Excellent resources explaining drought, drought indicators, impacts and monitoring techniques are available from the National Drought Monitor Center at the University of Nebraska-Lincoln.