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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) or Palmer Modified Drought Index (PMDI). Negative Palmer Index values indicate dry conditions, while positive values indicate wet conditions. Palmer Drought Index values generally fall between -6 and +6.

Palmer Drought Index Studies

Additional Palmer Drought Severity Index Studies

Other Data Archives