N˚ of Classes | Classes SPI | Interpretation |
1 | SPI > 2 | Humidity extreme |
2 | 1 < SPI < 2 | High humidity |
3 | 0 < SPI < 1 | Moderate humidity |
4 | −1 < SPI < 0 | Moderate drought |
5 | −2 < SPI < −1 | With drought |
6 | SPI < −2 | Extreme drought |