Table 5.2: Factors for use in deriving extreme rainfall information for preliminary scenario studies (screening assessments)
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| ARI (years) Duration | 2 | 5 | 10 | 20 | 30 | 50 | 60 | 70 | 80 | 90 | 100 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| < 10 minutes | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 |
| 10 minutes | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 | 8.0 |
| 30 minutes | 7.4 | 7.5 | 7.6 | 7.6 | 7.7 | 7.7 | 7.7 | 7.7 | 7.7 | 7.7 | 7.7 |
| 1 hour | 7.1 | 7.2 | 7.4 | 7.4 | 7.5 | 7.5 | 7.5 | 7.5 | 7.5 | 7.5 | 7.5 |
| 2 hours | 6.7 | 7.0 | 7.1 | 7.2 | 7.3 | 7.3 | 7.3 | 7.3 | 7.4 | 7.4 | 7.4 |
| 3 hours | 6.5 | 6.8 | 7.0 | 7.1 | 7.1 | 7.2 | 7.2 | 7.2 | 7.2 | 7.2 | 7.2 |
| 6 hours | 6.3 | 6.6 | 6.8 | 7.0 | 7.0 | 7.1 | 7.1 | 7.1 | 7.1 | 7.1 | 7.1 |
| 12 hours | 5.8 | 6.2 | 6.5 | 6.6 | 6.7 | 6.8 | 6.8 | 6.8 | 6.9 | 6.9 | 6.9 |
| 24 hours | 5.4 | 5.9 | 6.2 | 6.4 | 6.5 | 6.6 | 6.6 | 6.6 | 6.7 | 6.7 | 6.7 |
| 48 hours | 4.6 | 4.9 | 5.1 | 5.2 | 5.3 | 5.4 | 5.4 | 5.4 | 5.4 | 5.5 | 5.5 |
| 72 hours | 4.3 | 4.6 | 4.8 | 5.0 | 5.1 | 5.2 | 5.2 | 5.2 | 5.3 | 5.3 | 5.3 |
Note: This table recommends percentage adjustments to apply to extreme rainfall per degree Celsius of warming, for a range of average recurrence intervals (ARIs.). The percentage changes are mid-range estimates per degree Celsius and should only be used in a preliminary scenario study. The entries in this table for durations of 24, 48 and 72 hours are based on results from a regional climate model driven by an equilibrium climate model, and will be updated once regional model runs driven by transient climate models are available for New Zealand. The entries for 10-minute duration are based on the theoretical increase in the amount of water held in the atmosphere for a 1°C increase in temperature (8%). Entries for durations between 10 minutes and 24 hours are based on logarithmic (in time) interpolation between the 10-minute and 24 hour rates.
