| SPI value | Interpretation |
| 2.0 or more | 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 | Moderately dry |
| −1.5 to −1.99 | Severely dry |
| −2.0 or less | Extremely dry |