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Drought Variability

      US Drought Plot using PDSI          Dry Field Photo        PDSI time series plot

Drought variability is of crucial importance not only to farmers but also to people throughout the world who rely on food and resources from a region. Unfortunately, instrumental records provide only a limited picture of the size and severity of historical droughts as well as the factors impacting drought variability throughout the world.

Tree-ring data have been used to extend records of past drought. The tree-ring reconstructions show a more complete range of drought variability than is provided by the 20th century instrumental record. The extended records are useful for placing the instrumental period droughts into a longer time frame and for evaluating the rarity of the major 20th century, 1930s, and 1950s droughts in a broader temporal context.

The drought data are in the form of summer (June–August)​ averages of the Palmer Drought Severity Index (PDSI). Negative PDSI values indicate dry conditions, while positive values indicate wet conditions. PDSI values generally fall between -6 and +6.

Palmer Drought Severity Index Studies with Visualizations

Some of the PDSI reconstructions are available for visualization on NCDC's Live Access Server (LAS) page. Once on that page click the "Choose Dataset" button and then the "Paleoclimate - Drought Reconstructions" subdirectory to find the PDSI data. Plot settings can be modified using the "Set Plot Options" button and multiple years can be compared using the "Compare" button. Further information is available from the "Help" link in the upper right of the screen.

Additional Palmer Drought Severity Index Studies

Other Data Archives