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Table 1

Drought classification based on the SPI and SDI (Mckee et al. 1993; Nalbantis & Tsakiris 2009)

CategorySPI value
Extremely wet 2 ≤ SPI 
Very wet 1.5 ≤ SPI ≤1.99 
Moderately wet 1 ≤ SPI ≤1.49 
Near normal −0.99 ≤ SPI ≤0.99 
Moderately dry −1.0 ≤ SPI ≤ −1.49 
Severely dry −1.5 ≤ SPI ≤ −1.99 
Extremely dry SPI ≤ −2 
CategorySDI value
No drought 0 ≤ SDI 
Mild drought −1 ≤ SDI ≤0 
Moderate drought −1.5 ≤ SDI ≤ −1 
Severe drought −2 ≤ SDI ≤ −1.5 
Extreme drought SDI ≤ −2 
CategorySPI value
Extremely wet 2 ≤ SPI 
Very wet 1.5 ≤ SPI ≤1.99 
Moderately wet 1 ≤ SPI ≤1.49 
Near normal −0.99 ≤ SPI ≤0.99 
Moderately dry −1.0 ≤ SPI ≤ −1.49 
Severely dry −1.5 ≤ SPI ≤ −1.99 
Extremely dry SPI ≤ −2 
CategorySDI value
No drought 0 ≤ SDI 
Mild drought −1 ≤ SDI ≤0 
Moderate drought −1.5 ≤ SDI ≤ −1 
Severe drought −2 ≤ SDI ≤ −1.5 
Extreme drought SDI ≤ −2 
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