Twentieth Century Droughts
Name: _________________________________ Date: _____________
How has drought affected your state over the past century? Scientists use the Palmer Drought Severity Index (PSDI) to measure the extent of a drought. In this activity, you'll see how the index has been used to track droughts across the nation.
- Visit Historical Maps of the Palmer Drought Index. Over the past century, when was drought most severe in the United States?
When was drought most severe in your home state? - Next, each member of your class should choose a different state to investigate (not including Alaska or Hawaii). You can find out what the PSDI has been in the state you choose since 1900 by searching CLIMVIS, a climate resource from the National Climatic Data Center. First, pick a division in your state by looking at the State Division Maps. What state and division did you pick?
State __________________
Division ________ - Next, visit Selection Criteria for Displaying Period of Record. Select your state and division number. Leave the Parameter at "Palmer Drought Severity Index" and the Output Format at "GIF." Click the "Generate the Graph" button.
- Your graph should look like blue mountains and valleys. Print it. You can estimate the severity of a wet ("mountain") or dry ("valley") period by looking at its area. Larger areas mean more extreme wetness or drought. When were the two most extreme wet and dry periods? Find the approximate mid-point of these periods and record them in the table below.
For the State Division Wettest Driest Year Year - Compare drought in your division and state to surrounding areas. Visit Palmer Drought Severity Index by River Basin. What river basin does your division belong to? Be sure to refer back to State Division Maps to see where your division falls.
River Basin Number ________ - Click on the river basin that encompasses your division. You will see a graph of the percent area in your basin experiencing severe to extreme drought from 1895 to 1995. About what percentage of your river basin was also experiencing drought during the two dry years you listed in question 4?
For the River Basin Dry year (from question 4) Percent of river basin affected by drought - Are some areas of the U.S. more prone to drought than others? Visit Historical Maps of the Palmer Drought Index. Look at the map labeled 1895-1995. Which states are most prone to drought? The areas that are black and red have had more drought over the past century than other states. Which states are in the black and red zones?
- Look at the other maps on this page. Which time period maps show your state as being black or red? Write down these time periods. Do the two drought years you found in question 5 fall during any of these time periods?
