Statistical comparison between the standardized precipitation index and the standardized precipitation drought index


This study presents a statistical comparative study between two indices using only precipitations as a calculation parameter, the standardized precipitation index (SPI) and the standardized precipitation drought index (SPDI). The first is widely used in research and in monitoring drought on several time scales. While the second was a new drought indicator but very little is used. At the moment when collecting climate data in Algeria poses several problems, in terms of accessibility to weather stations, the punctuality of collecting agents, the calculations of drought indices based on several meteorological parameters seem very difficult if not impossible. For this, the study of drought, based on only two parameters (precipitations), seems to us as an advantage. The comparison between the two indices is based on four statistical operations, on three-time scales (3, 12 and 24 months): the simple statistical description, the comparison of the frequencies of dry and wet periods, the degree of correlation and a test on equal variances. The results show that the two indices correlate significantly in fairly long drought periods (12 months) and diverge on the other two time scales.

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Correspondence to Nabil Mega.

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Mega, N., Medjerab, A. Statistical comparison between the standardized precipitation index and the standardized precipitation drought index. Model. Earth Syst. Environ. 7, 373–388 (2021).

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  • Algerian high plateaus
  • Drought
  • Statistical comparison
  • SPI
  • SPDI