| SPI range | Drought category |
| >2 | Extremely wet |
| 1.5 to 1.99 | Severely wet |
| 1.0 to 1.49 | Moderately wet |
| 0.99 to 0 | Mildly wet |
| 0 to -0.99 | Mild drought |
| −1.0 to −1.49 | Moderate drought |
| −1.5 to −1.99 | Severe drought |
| <−2 | Extreme drought |