How Much Water is Available in the Atmosphere for Precipitation?

precipitation falling from a cloud

Image courtesy Tracy Hagen, Perth, Australia

To explore the relationship between the amount of water in the atmosphere available for precipitation and the actual precipitation observed by satellite
Grade Level: 7-12
Estimated Time for Completing Activity: 2 50-minute periods
Learning Outcomes:
  • Students will examine global moisture and precipitation
  • Students will examine seasonal changes in precipitation
  • Students will practice finding data using Internet resources
  • Discussion of Earth’s water budget or cycle
  • Familiarity with Internet access and computer use
  • Computers with Internet access
  • Printer or overhead projector
Lesson Links:

Water is one of Earth’s most unique and valuable resources. Thus, the distribution of water on Earth is a very important factor in the evaluation of global climate and its impact on life. For decades, scientists have observed, measured and studied the water budget of Earth by examining water from oceans, lakes, rivers and glaciers. The atmosphere also plays an important role in the water budget by the processes of evaporation and precipitation, so scientists also collect data on atmospheric water vapor, cloud water, rainfall and snowfall by satellite.

In this lesson, you will use historical satellite data to examine precipitable water — a measure of the water available in the atmosphere from evaporation (in the form of water vapor). You will then compare precipitable water (which is expressed as a depth in cm) to the observed precipitation (which is expressed as a rate in mm per day).


Pre-Lesson Inquiry Activity (Optional)
1. Predict which layer of the troposphere might contain more precipitable water: upper or lower? Explain your prediction to your class.
2. How might that prediction relate to amount of precipitation? Explain your prediction to your class.
3. Predict how the amount of precipitation might vary with changing seasons. Explain as before.

Part I: Find Precipitable Water data

1. Click on the link above to the MY NASA DATA Live Access Server Advanced Edition.
2. Click the Choose Dataset tab at the top left menu bar.
3. Click Atmosphere, Atmospheric Water Vapor, then Monthly Lower Troposphere Precipitable Water Vapor.
4. A color-plot of a global view will appear in the window. Global view is the Default, so no change should be needed.
5. Under Maps, choose Latitude-Longitude, which may already be showing.
6. Under Date, choose the month and year that you want to study.
7. Click on the Update Plot tab from top menu.
8. Save and rename the file on your desktop, or Print (using tab on top right of menu bar) for later discussion.
9. Repeat Steps 2-8, except choose Monthly Upper Troposphere Precipitable Water Vapor.

Part II: Find Precipitation data

1. Return to the MY NASA DATA Live Access Server Advanced Edition (may already be open).
2. Click on Choose Dataset, then select Atmosphere, Precipitation, Monthly Precipitation (GPCP).
3. The global view color-plot will appear. To view in same perspective as in Part I, click and slide world map, located in left menu above the compass rose, until it in same position as in Part I.
4. Under Maps, select Latitude-Longitude (Default) as before.
5. Under Date, select the same month and year as in Part I.
6. Click on Update Plot.
7. Save and rename file on desktop, or Print for later discussion.


1. Compare the values for lower and upper atmospheric precipitable water. Which layer of the atmosphere contains the most water vapor? Why?

2. For your particular month, do you notice a comparable pattern in the color contours between precipitable water and precipitation rate? What region of the Earth has the most precipitation and precipitable water?

3. Given the season for your monthly data, are the results what you would expect? As a class, discuss the seasonal changes in precipitation throughout a particular year.

4. Can you draw any conclusions about the weather patterns and climate for different regions of the globe?


1. Instead of examining a global map, select a particular region to study. Return to the Live Access Server and use the Select Region tool from the left-hand menu (small rectangle icon). Instead of Full Region, select a different option. Discuss the resulting graphs.

2. Examine a particular location on Earth, perhaps your location. Return to the Live Access Server and choose same datasets.

3. The datasets may be saved individually in an ASCII file output. After choosing the dataset, location, and date, click the Save As button from top menu. Save the files as ASCII files. These can then be input to a spreadsheet to allow exploration of all three variables at once. You might want to add Lower and Upper Troposphere Precipitable Water Vapor to obtain the total water vapor available in the atmospheric column, and compare this with precipitation.

Lesson plan contributed by Carl Hendricksen, Dunlap, Illinois

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