Climate change Print

​​​Climate change is expected to alter the intensity and frequency of significant rainfall events. 

In general, an increase of peak flow is expected. Hydrological calculations shall be carried out in accordance with Auckland Regional Council technical publication TP108 (Guidelines for Stormwater Runoff Modelling in the Auckland Region) with allowances for climate change effects in accordance with Table 5.2 of Climate Change Effects and Impact Assessment: A Guidance Manual for Local Government in New Zealand (Ministry for the Environment, 2008), using a temperature increase of 2.1 degrees by 2090. This includes an increase to the 24-hour rainfall depth, as well as a change to the dimensionless TP108 rainfall profile as shown in Table 4.1 and Table 4.2.​​

Table 4.1: Percentage Increase in 24-hour Design Rainfall Depth 

Annual Exceedance Probability (AEP)

Percentage Increase in 24-Hour Design Rainfall Depth Due to Future Climate Change*

50%

9.0%

20%

11.3%

10%

13.2%

5%

15.1%

2%

16.8%

1%

16.8% ​

​* assuming 2.1°C increase in temperature

Table 4.2: TP108 Normalised 24-hour Temporal Rainfall Intensity Profile​

Time (hrs:mins)

Time Interval (min)

TP108 Normalised Rainfall Intensity (I/I24)

Existing Condition

Future Climate Change*

0:00 – 6:00

 

360

0.34

0.33

6:00 – 9:00

 

180

0.74

0.73

9:00 – 10:00

60

0.96

0.95

10:00 – 11:00

60

1.40

1.40

11:00 – 11:30

30

2.20

2.20

11:30 – 11:40

10

3.80

3.82

11:40 – 11:50

10

4.80

4.86

11:50 – 12:00

10

8.70

8.86

12:00 – 12:10

10

16.20

16.65

12:10 – 12:20

10

5.90

5.95

12:20 – 12:30

10

4.20

4.24

12:30 – 13:00

30

2.90

2.92

13:00 – 14:00

60

1.70

1.70

14:00 – 15:00

60

1.20

1.19

15:00 – 18:00

180

0.75

0.75

18:00 – 24:00

360

0.40

0.39

* assuming 2.1°C increase in temperature​

The performance of stormwater systems in coastal areas shall take into account expected future sea levels. Refer to Section 4.3.5.8 below.​​

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