The effect of the length of record on the standardized precipitation index calculation

The effect of the length of record on the standardized precipitation index (SPI) calculation was investigated by examining correlation coefficients, the index of agreement, and the consistency of dry/wet event categories between SPI values derived from different precipitation record lengths. The eff...

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Bibliographic Details
Published in:International journal of climatology 2005-03, Vol.25 (4), p.505-520
Main Authors: Wu, Hong, Hayes, Michael J., Wilhite, Donald A., Svoboda, Mark D.
Format: Article
Language:English
Subjects:
Earth sciences
Earth, ocean, space
Exact sciences and technology
External geophysics
gamma distribution
Hydrology
Hydrology. Hydrogeology
length of precipitation record
Meteorology
Nebraska
standardized precipitation index (SPI)
time scale
Water in the atmosphere (humidity, clouds, evaporation, precipitation)
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Summary:The effect of the length of record on the standardized precipitation index (SPI) calculation was investigated by examining correlation coefficients, the index of agreement, and the consistency of dry/wet event categories between SPI values derived from different precipitation record lengths. The effect was also illustrated by comparing SPI values derived from different lengths of record in some severe drought and flood years, and by comparing drought intensities based on SPI values temporally and spatially. Furthermore, the reason for the SPI value discrepancy was explored by investigating the changes of the shape and scale parameters of the gamma distribution when different lengths of record were involved. The gamma distribution is a frequency distribution of climatological precipitation time series and is the basis of the SPI calculation used in this analysis. The results show that SPI values computed from different lengths of record are highly correlated and consistent when the gamma distributions of precipitation over the different time periods are similar. However, the SPI values are significantly discrepant when the distributions are different. It is recommended that the SPI user should be aware of the numerical difference of the SPI values if different lengths of record are used in interpreting and making decisions based on SPI values. Copyright © 2005 Royal Meteorological Society.
ISSN:0899-8418
1097-0088
DOI:10.1002/joc.1142