Arid Lands Newsletter (link)No. 52, November/December 2002
Special issue: Selected papers from the IALC Conference:
Assessing Capabilities of Soil and Water Resources in Drylands:
The Role of Information Retrieval and Dissemination Technologies
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Ffolliott et al: Sidebar 1: the Palmer drought index

The Palmer drought index (Palmer 1965) is used as an indicator of drought severity and a particular index value is often the signal to begin or discontinue a drought contingency plan (Lohani and Longanathan 1997). A drought is defined (by this index) as a time interval of time in the order of months or years in duration during which the actual moisture supply at a location consistently falls short of the climatically appropriate moisture supply. The severity of a drought is considered to be a function of both the magnitude and frequency of the moisture deficiency. While other drought indices have been developed to give (theoretically) better representations of relative wetness and dryness than the Palmer indices (McKee, Doeskin and Kleist 1993, 1998), the Palmer drought index and its variations have been used for monitoring and decision-making for decades and, therefore, are familiar to the user community. If other drought indices are to replace the Palmer indices, comparisons of the characteristics of the respective indices will be necessary so that users can transfer their familiarity with the Palmer index to the other indices (Guttman 1998).

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