Designing for Climate Change

Use NIWA’s HIRDS tool for the most accurate rain intensity figures. The HIRDS tool shows figures for historical rainfall intensities and predicted rainfall based on the anticipated effects of climate change, expressed as Representative Concentration Pathways (RCP) levels.

The increased rainfall intensity in a worst-case scenario is typically 11 – 13% higher than historical levels, mostly occurring under the least intense (RCP 2.6) value. To ensure design calculations account for expected climate change, use the most appropriate RCP level.

RCP Level Descriptions

Rating	Description
RCP 2.6	A very stringent pathway that assumes CO2 levels peak at 2020 and go to zero by 2100.
RCP4.5	An intermediate scenario where CO2 levels peak by 2040, then decline due to the decreased availability of fossil fuels.
RCP 6.0	A stabilisation scenario, where CO2 emissions peak around 2080, then decline with the deployment of various technologies and strategies.
RCP 8.5	Worst-Case scenario where CO2 emissions continue to rise throughout the 21st century. Thought by some to be based on an overestimation of projected coal outputs.

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Example of RCP Values for Randomly Selected Locations

Location	Historic	RCP 2.6	RCP 4.5	RCP 6.0	RCP 8.5	% change
Whangarei	137	147	150	149	152	11
Auckland Central	121	131	133	132	135	12
Mt Maunganui	149	161	164	163	167	12
Waikanae	107	116	118	117	120	12
Christchurch	55	59	60	60	61	11
Dunedin	71	77	79	78	80	13
Queenstown	55	59	60	60	61	11
Huntly	126	136	138	137	140	11
Nelson	114	124	126	125	128	12
Silverdale	124	134	136	135	138	11

Visit NIWA HIRDS-tool to get the corresponding values for specific locations.

Example of increasing ARI figures Using RCP Values from Random Locations