Drought & the Palmer Index

Drought happens - again and again. The Palmer Drought Severity Index was developed in 1965 by Wayne Palmer of the Department of Climatology in the U.S. Weather Bureau. The index is a measure of the difference in soil moisture content from the average for a particular location at a particular time. The index is scaled from values of roughly -6.00 indicating extreme drought to +6.00 for extremely wet soil conditions.¹ One of the major advantages of the Palmer Scale is to see measures of soil moisture over time; that is, in historical perspective. And that is the point of the following exercise - to see the drought conditions of the 1930s in a small region of the Great Plains in the context of a century's worth of climatic conditions.

You are going to look at drought conditions in the southwest corner of Kansas over the course of the 20th century using Palmer Drought Severity Index data. There is no need to print the entire file. You can view the data on your computer screen as you work.

Print two copies of the PDSI Graph Paper. You are going to start by graphing Palmer data for the decades of the 1920s and 1930s following the example below for the first few years of the 20th century.

To Start You Thinking

1) Based on your graphs, what observations can you make about drought conditions in southwest Kansas over these two decades?

2) Within your group or class divide up the remaining decades of the 20th century and prepare Palmer graphs. Post the graphs in order on a wall so that you can study them.

3) Are there other periods of drought as serious as that in the 1930s in terms of either duration or degree? Explain. When would it have been good to be a winter wheat farmer in southwest Kansas over the last century?

4) Describe any patterns you see in the incidence of drought in southwest Kansas over the last 100 years.

5) Click through the rainfall maps available in this series of slides. Compare the map images with the data in your Palmer graph. Describe your observations.