Case Study: Where Does the Water Go?

Floods in the Midwest! Drought in the Southeast and the West! Record snowfall in the East!

All these statements could easily show up as headlines in most regional newspapers. But, think about this...the Midwest doesn't stay flooded, the Southeast and West does get some rain and the East doesn't stay buried in snow; why not? Where does all the precipitation go and how does it get there? These are the questions you will be working on answering in this chapter.


In this chapter, you'll begin to think about the relationship between annual precipitation patterns across the continental United States and annual evaporation and surface runoff patterns. Because precipitation, evaporation, and runoff 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, Depending on location and time of year (i.e., seasons) these two may not always balance. In some cases evaporation rates might actually be greater than precipitation rates or precipitation rates could be greater than evaporation rates. You will investigate how the patterns of precipitation, evaporation, and surface runoff are similar and how they are different. You will make a map table showing annual precipitation amounts, comparing them to annual evaporation and annual surface runoff across the United States. Then you will examine specific cities and make a chart of how these variables compare to one another.

Here is a simple diagram that may be helpful in thinking about how the three datasets you will look at here are related. Image Source: USGS




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