Monday, April 23, 2018

National Drought Mitigation Center

Climate Division Standardized Precipitation Index (SPI)

Archived Maps - view climate division based 1-12-, 15-, 18-, 24- 30-, 36-, 48-, 60- and 72-month, and year-to-date SPI maps (updated monthly) going back to 1980.


The Standardized Precipitation Index (SPI), developed by T.B. McKee, N.J. Doesken, and J. Kleist and in 1993, is based only on precipitation. One unique feature is that the SPI can be used to monitor conditions on a variety of time scales. This temporal flexibility allows the SPI to be useful in both short-term agricultural and long-term hydrological applications.

Calculating the SPI

The Western Regional Climate Center uses precipitation data from the National Climatic Data Center (NCDC) to calculate SPI values for each climate division. The information is then reclassed and mapped at the National Drought Mitigation Center using a Geographic Information System. The maps are based on preliminary precipitation data, and the data’s source and methods used in incorporating the data into a final product must be considered carefully when analyzing these maps. “Interpretation of SPI Maps” explains how to interpret the maps at various timescales. The SPI program and sample files are available for downloading.

Example SPI Map

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