Part 4 - Analyze the Data

Step 1 – Compare Values in the Map Table

1. You now have a completed map table in the Table tab. These maps are synchronized so that if you click on one, a point will appear on each map. You can get the value for the data at that point on all three maps by reading the legend below each map. Try clicking on a few different places to see how the values compare.
   
   
   
   
2. Create a chart like the one below or download this Microsoft Excel spreadsheet template: Water_Availability.xls (Excel 40kB Sep22 09) to create a graph of different cities around the US.
   
   
   
   

Step 2 – Reflect on the Analysis Questions

1. Question: In general, what is the relationship between surface runoff and precipitation in regions that receive high amounts of annual precipitation? What is the relationship between surface runoff and precipitation in regions that receive low amounts of annual precipitation?
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Answer: In general, it appears that high runoff areas are also high precipitation areas, although there are exceptions. For example, Florida receives high amounts of precipitation but has low total surface runoff. In general, areas with low annual precipitation also have low amounts of surface runoff.





2. Question: Identify an area of the U.S. where total annual surface runoff is high even though total annual precipitation is only medium. What are possible processes or factors that cause surface runoff to be high for this area?
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Answer: The Rocky Mountains have high amounts of surface water runoff even though they have moderate amounts of annual precipitation. Much of the precipitation in the Rocky Mountains falls as snow, which tends to runoff as surface water when it melts.





3. Question: Identify an area of the US where the total annual surface runoff is low even though the annual precipitation is high. What are some possible processes or factors that cause surface runoff to be low for this area?
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Answer: Florida and parts of Georgia, South Carolina, Alabama, and Mississippi have high annual precipitation amounts and low annual surface runoff amounts. Annual evaporation tends to be very high in these areas in part due to the high average temperatures in the Southeastern U.S. The geology of the area also plays a role.