68 lines
2.8 KiB
Text
68 lines
2.8 KiB
Text
National Environmental Public Health Tracking Network
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Standard Precipitation Index (SPI) Metadata
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Publication Date
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01/11/2017
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Background
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The Standardized Precipitation Index (SPI) is a widely used index to characterize
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meteorological drought ona range of timescales. On short timescales, the SPI is closely
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related to soil moisture, while at longer timescales, the SPI can be related to
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groundwater and reservoir storage. The SPI can be compared across regions with
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markedly different climates. It quantifies observed precipitation as a standardized
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departure from a selected probability distribution function that models the raw
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precipitation data. The raw precipitation data are typically fitted to a gamma ora
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Pearson Type III distribution, and then transformed to a normal distribution. The SPI
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values can be interpreted as the number of standard deviations by which the observed
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anomaly deviates from the long-term mean. The SPI can be created for differing periods
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of 1-to-36 months, using monthly input data. For the operational community, the SPI has
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been recognized as the standard index that should be available worldwide for
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quantifying and reporting meteorological drought. The dataset includes one-month SPI
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values for every contiguous US county and the District of Columbia monthly from 1895-
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2016.
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The dataset has been compiled to estimate wetness and dryness of a particular area.
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This is important for the agriculture as well as health sectors. The data can be used to
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examine local and national trends in drought information.
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Data Values
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Range from -3 (dry) to +3 (wet). 0 indicates normal conditions. Missing data is noted as
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-99,99,
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Geographic Scale
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Data includes all counties in the lower 48 states plus the District of Columbia.
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& Scope
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Time Period January 1, 1895 — December 31, 2016. Known to be accurate as of time period end date.
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Raw Data Data downloaded from the National Oceanic and Atmospheric Administration (NOAA)
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Processing server and were originally provided as monthly values at a 5km grid. Distance weighting
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functions were applied to constrain the drought values to a specific US county.
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No data were lost or omitted during calculation. All data that were available were used.
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Data will be updated on an ad hoc basis, when necessary.
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Additional Keyantash, John & National Center for Atmospheric Research Staff (Eds). Last modified
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Information 02 Mar 2016. "The Climate Data Guide: Standardized Precipitation Index (SPI)."
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Retrieved from https://climatedataguide.ucar.edu/climate-data/standardized-
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precipitation-index-spi.
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McKee, T.B., N. J. Doesken, and J. Kliest, 1993: The relationship of drought frequency and
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duration to time scales. In Proceedings of the 8th Conference of Applied Climatology, 17-
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22 January, Anaheim, CA. American Meterological Society, Boston, MA. 179-18
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