Comparison of SPI and SPImod in Drought Monitoring of Several Climatic Samples of Iran

Nadi, Mehdi; Soqanloo, Saeid Shiukhy

doi:10.52547/jwmr.11.21.108

Cited by 2 publications

(2 citation statements)

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“…Assuming that the precipitation data follow the gamma distribution, this distribution is then fitted to the monthly cumulative precipitation time series by default. Then, the probability obtained from the cumulative gamma distribution is applied to the standard normal distribution (mean 0 and variance 1) and the corresponding number of probabilities is used as the SPI (Nadi & Shiukhy Soqanloo, 2020).…”

Section: Standardized Precipitation Indexmentioning

confidence: 99%

“…On the other hand, F I G U R E 1 Ambrothermic diagrams of studied meteorological stations (months with the temperature curve above the precipitation curve are called dry months). Bazrafshan et al (2015) and Nadi and Shiukhy Soqanloo (2020) proposed a more suitable alternative distribution function than the default gamma distribution function in Iran. Therefore, eight probability distribution functions were used for rainfall data: Normal (N), Log-Normal (LN), Gamma (G), Weibull (W), Exponential (E), Extreme Value (EV), General Extreme Value (GEV), and General Pareto (GP).…”

Section: Modified Standardized Precipitation Indexmentioning

confidence: 99%

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Modification of standardized precipitation index in different climates of Iran

Nadi,

Shiukhy Soqanloo

2023

Meteorological Applications

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The most popular metric for drought monitoring is the standardized precipitation index (SPI). It does have some drawbacks, though, such as using gamma probability distribution function as the default distribution and not taking into account seasonal variations. The effectiveness of SPI in monitoring droughts in various Iranian climates was examined in this study, and in order to address its limitations, it was contrasted with the modified SPI (mod‐SPI). Then, the performance of the mod‐SPI and SPI in drought monitoring was compared with nine meteorological stations throughout Iran during the period 1956–2010. The results showed that the gamma distribution function was not selected in any of the 12 timescales (TS) considered at the studied meteorological stations. Based on the Cohen's kappa index analysis, there is a clear difference between the SPI and mod‐SPI in monitoring drought classes, which is more evident at low TS (less than 6 months), but at much higher TS (above TS‐9), the two indices almost coincide. The results showed that in the arid and semiarid areas, the SPI and mod‐SPI are significantly different, so it seems that the SPI monitors aridity rather than drought. The results imply that using mod‐SPI instead of SPI provides more accurate drought monitoring by eliminating the seasonal effects of precipitation data. Considering the low efficiency of SPI in short‐term drought monitoring (less than 9 months) in arid and semiarid regions, it is recommended to use mod‐SPI instead of SPI in most parts of Iran, especially on the southern coasts of Iran.

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Section: Standardized Precipitation Indexmentioning

confidence: 99%

Section: Modified Standardized Precipitation Indexmentioning

confidence: 99%