AgriMetSoft


What are the advantages and disadvantages of using SPI (standardized precipitation index)?

According to Hayes et al. (1999), the SPI has three main advantages and three main disadvantages. The advantages of using SPI are: 1- simplicity; the SPI is based on rainfall, 2- its standardization, which ensures that the frequency of extreme events at any location and on any time scale is consistent, 3- variable time scale, which is helpful for the analysis of drought dynamics, especially the determination of onset and cessation, which have always been difficult to track with other indices (Angelidis et al., 2012). The SPI has three disadvantages (Hayes et al. 1999), namely 1- the assumption that a suitable theoretical probability distribution can be found to model the raw precipitation data, these distributions have different feedbacks, and they can make different result. Therefore, McKee et al. (1993) recommend using at least 30 years of high quality data, 2- the standardized nature of the index itself; the SPI is not capable of identifying regions that may be more ‘drought prone’ than others; equal value of SPI at two different locations does not necessarily imply equal water deficit at these two locations (Angelidis et al., 2012), and 3- when running the SPI at short time scales (1, 2, or 3 months) to regions of low seasonal precipitation, misleadingly large positive or negative SPI values may result.

McKee TB, Doesken NJ, Kleist J. 1993. The relationship of drought frequency and duration to time scales. In Proceedings of the 8th Conference on Applied Climatology, Anaheim, CL, 17-22 January, 179-183.

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