| Variable | Evaluation grade | |||
| Low | Moderate | High | Very high | |
| Trigger factor for heavy rain (mm) | ≤100 | >100 and ≤285 | >285 and ≤490 | >490 |
| (0 - 0.25) | (0.26 - 0.5) | (0.51 - 0.75) | (0.76 - 1) | |