Teaching Notes

Example Output

Example Output
Map and output from FieldScope GIS. Click the image for a larger view.

This example shows three different views of the United States created from FieldScope GISeach from the Globe Watersheds Module 1: Annual Evaporation, Annual Surface Runoff, and Annual Precipitation.

Grade Level

This chapter is appropriate for students in grades 6 through 12.

Learning Goals

After completing this chapter, students will be able to:

Background Information

Because precipitation and evaporation are components of the global water cycle, the total amount of water is constant over time with equal rates of precipitation and evaporation world-wide, but depending on location and time of year (i.e. seasons) these two may not balance with evaporation actually being greater than the precipitation. Students will explore precipitation and evaporation amounts across the U.S. As they collect data for study cities, they should recognize that there is not always a balance between the two components at a specific location. Some of the imbalance is the result of seasonal factors. For example, when precipitation occurs as snow during the winter, it doesn't contribute to surface runoff and evaporation as readily as when it melts during the spring. But, some of the imbalance may be due to the fact that there are regional or global factors involved.


Evaporation is a physical process by which a liquid or solid substance is transformed to the gaseous state. Evaporation represents the return of precipitation back into the atmosphere. Like precipitation, evaporation is not evenly distributed by location. The main sources of water vapor in the lower atmosphere are evaporation from Earth's surface and transpiration by plants.

Major factors influencing the rate of evaporation include atmospheric temperature, wind, atmospheric humidity, and the availability of water. Other contributing conditions and factors may include the following:

Surface Runoff

Surface runoff is the water that flows down creeks, streams and rivers. Precipitated water that has not evaporated back into the atmosphere or infiltrated into the ground runs off as surface water.

Major processes and factors influencing the timing and quantity of surface runoff include the amount of precipitation, rate of precipitation, form of precipitation (snow, rain, sleet, hail, etc), season the precipitation fell, infiltration rate, degree of ground saturation, land use and ground cover, and geology.

Instructional Strategies

Before the students begin this investigation, ask them to develop a working hypothesis describing the relationship between total annual precipitation and total annual evaporation. Will areas with high precipitation have high evaporation rates? Will areas with low precipitation, such as the hot, arid west, also have high total annual evaporation? Write the various hypotheses down on the class whiteboard so that students can refer back to them as they work through the GIS analysis.

As part of this investigation, students fill out a table of annual precipitation, evaporation, and surface runoff, for four pre-selected cities as well as three of their choice. One extension of this activity is to graph the data using Excel or other graphing/charting program. The chart can help students visualize the relationships of these different variables across the country. One important relationship for them to observe is how little surface runoff occurs compared to evaporation.

An Excel spreadsheet has been created for this purpose. Click here to download: Water_Availability.xls (Excel 40kB Sep22 09) After downloading and opening, click on the Investigation III tab at the bottom of the sheet to open the appropriate table and chart. Blank cells are in the table for students to add their selected cities. Below is an example of the data from the four pre-selected cities in the Investigation.

Another option is to have students create the chart on graph paper.


Science Standards

The following National Science Education Standards are supported by this chapter:

Grades 5-8

Science as Inquiry

Earth and Space Science

Grades 9-12

Science as Inquiry

Earth and Space Science

Science in Personal and Social Perspectives

Geography Standards

The following U.S. National Geography Standards are supported by this chapter:

The World in Spatial Terms

1. How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective

Physical Systems

7. The physical processes that shape the patterns of Earth's surface

The Uses of Geography

18. How to apply geography to interpret the present and plan for the future

Other Standards

The following National Technology Foundation Standards are supported by this chapter:

Time Required

Up to 1 hour

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