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Palmer Drought Index
In 1965, Wayne Palmer developed a drought index which built upon decades of earlier attempts to define and monitor drought. Palmer's index was revolutionary because, for the first time, it expressed drought and wet spells as a standardized index reflecting the imbalance between water supply and water demand. Many new drought indices have been developed since then, with some utilizing satellite observations and more sophisticated computer models among other things. The U.S. Drought Monitor incorporates information from all of these indices as well as drought impacts in depicting drought.