Advantages And Disadvantages Of Standardized Precipitation Index (SPA)

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Meteorological drought is referred as a precipitation deficiency, in comparison to normal or base line condition. We use Standardized Precipitation index (SPI-n, where n = 3, 6, 9 and 12 months accumulation period) as an index of meteorological drought. SPI represents a statistical z-score or the number of standard deviations (following a probability distribution, usually Gamma and back transformed to standard normal distribution) above or below that an event is from the mean (McKee et al. 1993; Sims et al., 2002). SPI is spatially invariant and probabilistic in nature and able to capture different drought states ranging from short, medium and long-term drought conditions depending on the length of the accumulation period. SPI has number of advantages, such as (Lloyd-Hughes and Saunders, 2002); (i) The SPI is based on precipitation and requires computation of only two …show more content…

(iii) It can be tailored to specific needs for impact assessment. For example, it’s variable time scales are useful for modelling wide range of meteorological, agricultural, and hydrological applications. The temporal nature of the index facilitates understanding drought dynamics, such as onset and cessation, which is difficult to be tracked by other indices. (iv) Standardized nature ensures that the frequency of extreme events at any location and on any time scale is consistent. Conversely, application of SPI has few potential disadvantages: (i) the quantity and reliability of the data used to fit a suitable probability distributions. (ii) Due to standardized nature, SPI is incapable of identifying regions that are more “drought prone” than others, and (iii) Employing SPI at shorter time scales (such as, 1, 2, and 3 months) to the regions with low seasonal precipitation, resulting into erroneous large positive or negative SPI

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