Index | Non-drought | Mild-drought | Moderate drought | Severe drought | Extreme drought |
SPI | −0.5 < SPI | −1.0 < SPI ≤ −0.5 | −1.5 < SPI ≤ −1.0 | −2.0 < SPI ≤ −1.5 | SPI ≤ −2.0 |
SPEI | −0.5 < SPEI | −1.0 < SPEI ≤ −0.5 | −1.5 < SPEI ≤ −1.0 | −2.0 < SPEI ≤ −1.5 | SPEI ≤ −2.0 |