Palmer Drought Severity Index

The Palmer Drought Severity Index (PDSI) for 1934 shows widespread drought. The PDSI is based on precipitation and temperature data. Scientists can use the index to show rainfall deficits (compared to normal rainfall amounts) for certain areas or time periods. This graphic is based on maps from the National Oceanic and Atmospheric Administration’s Paleoclimatology Program. Using an interactive tool, you can view PDSI maps for the United States for any year from 1895 to 1995.