When Precipitation Patterns Change

Part C. How is Drought Measured?

  1. Go to the Current Conditions webpage (link will open in a new window). Scroll down through the list and explore some of links to get a sense of all the maps and data products that are available for tracking drought.
  2. Read the about Drought Classification and Indicators at the About the Data page from the US Drought Monitor (link will open in a new window).
  3. Stop and Think

    11. Use your own words to describe what a drought index is.
    12. What are some of the parameters that are commonly taken into account in calculating drought index values?
  4. Several different Drought Indices have been developed, and each has its own strengths. We'll look at an index that has been widely used in agricultural regions of the U.S. Go to the National Weather Service's page on the Palmer Drought Severity Index (PDSI) to learn more about this index.

    Checking In

    • What is the main parameter on which the PDSI is calculated?
    • Describe the range of values for the PDSI. Do positive values represent wet or dry conditions?
    palmer drought map May 2016 Palmer Drought Severity Image for the month of May 2016.
  5. Look at the PDSI map on the right (click the image for a larger view). It shows conditions for the month of May 2016. Use the color legend to interpret the conditions that existed across the contiguous U.S. at that time. Based on your interpretation, predict what might have been occurring at that time?

Stop and Think

13. Access and interpret the current PDSI map image. Write a description of current drought status for areas across the U.S.