Standardized Precipitation Index (SPI-3)
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Suggested citation
McKee, T.B., N.J. Doesken and J. Kleist. 1993. The relationship of drought frequency and duration to time scale. In: Proceedingsof the Eighth Conference on Applied Climatology, Anaheim, California, 17–22 January 1993. Boston, American Meteorological Society, 179–184. https://www.droughtmanagement.info/literature/AMS_Relationship_Drought_…
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Cautions
The exact relationship between the accumulation period and the drought impact depends on the natural environment (e.g., geology, soils) and the human interference (e.g., existence of irrigation schemes). In order to get a full picture of the potential impacts of a drought, the SPI should be calculated and compared for different accumulation periods. A comparison with other drought indicators is also needed, in order to evaluate the actual impacts on the vegetation cover and different economic sectors. SPI is based only on precipitations and does not address the effects of high temperatures on drought conditions. The SPI should be interpreted with care in arid regions (high probability of zero rainfall) where the concept of drought needs to be adapted, or analysed with alternative drought indicators.