NIWA Weather Files

NIWA Weather Files files were developed by the National Institute of Water and Atmospheric Research (NIWA) and subsequently reviewed and tested by technical specialists from the Building Research Association of New Zealand (BRANZ) and Kāinga Ora – Homes and Communities. The Ministry of Business, Innovation and Employment (MBIE) officially released the weather files in October 2024.

Types of Weather File

Typical Meteorological Year (TMY3) Files for the Present Climate

The TMY3 files represent typical climate conditions in Aotearoa New Zealand as of 2024, replacing the older TMY2 files created by NIWA in 2008.

A TMY3 file contains hourly weather data for an artificial year composed of 12 representative months. Each selected month is typical of that month's weather over a period of 10 years or more. These files are designed for:

• Building energy and thermal performance analysis.

• Demonstrating compliance with Building Code clause H1 Energy Efficiency, using modeling methods described in verification methods H1/VM1 and H1/VM2.

Design Summer Year (DSY1) Files for the Present Climate

The DSY1 files represent a year with a moderately warm summer, warmer than typical for the location, with an approximate return period of 7 years.

These files are specifically used to assess overheating risks in buildings. For example, the Chartered Institute of Building Services Engineers’ (CIBSE) technical memorandum TM59 outlines a design methodology for evaluating overheating risk in homes. Unlike TMY3 files, DSY1 files include a single year's observed data rather than synthesized data from multiple years.

These files contain detailed meteorological data collected from various weather stations and observation points. They typically include information on temperature, humidity, wind speed and direction, solar radiation, precipitation, and other atmospheric variables.

Future-Projected Climate TMY3 and DSY1 Weather Files

In addition to present-climate TMY3 and DSY1 files, NIWA provides future-projected weather files for three different climate change scenarios based on Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathways (SSP). These scenarios simulate potential climate conditions for specific timeframes:

• M1 (SSP1-2.6 for 2040): Mean temperature increase: +0.5°C from present day (2024), or +1.5°C above pre-industrial levels.

• M2 (SSP2-4.5 for 2050): Mean temperature increase: +1.0°C from present day (2024), or +2.0°C above pre-industrial levels.

• M3 (SSP3-7.0 for 2070): Mean temperature increase: +2.0°C from present day (2024), or +3.0°C above pre-industrial levels.

Climate Zones

The 18 climate zones align with territorial authority boundaries, except for the Rangitikei and Waitaki districts. These zones are subsets of the six climate zones defined in the acceptable solutions and verification methods for Building Code clause H1.

Each weather file is identified by a two-letter code in its file name, corresponding to the climate zone it represents. The map above illustrates the placement of these zones within the six H1 climate zones. The detailed breakdown is as follows:

H1 Climate Zone 1:

• ‘NL’ - Covers the Far North District, Whangārei District, and Kaipara District. Based on weather data from Kaitāia.

• ‘AK’ - Includes Auckland and the Thames-Coromandel District. Based on weather data from Auckland.

• ‘BP’ - Encompasses the Western Bay of Plenty District, Tauranga City, Whakatāne District, Kawerau District, and Ōpōtiki District. Based on weather data from Tauranga.

H1 Climate Zone 2:

• ‘HN’ - Covers the Hauraki District, Waikato District, Matamata-Piako District, Hamilton City, Waipā District, Ōtorohanga District, South Waikato District, and Waitomo District. Based on weather data from Hamilton.

• ‘NP’ - Includes the New Plymouth District, Stratford District, South Taranaki District, and Whanganui District. Based on weather data from New Plymouth.

• ‘EC’ - Encompasses the Gisborne District, Wairoa District, Hastings District, Napier City, and Central Hawke’s Bay District. Based on weather data from Napier.

H1 Climate Zone 3:

• ‘MW’ - Covers part of the Rangitikei District south of 39°50'S (-39.83), the Manawatu District, Palmerston North City, Horowhenua District, and Kāpiti Coast District. Based on weather data from Paraparaumu.

• ‘WN’ - Includes Porirua City, Hutt City, and Wellington City. Based on weather data from Wellington.

• ‘NM’ - Encompasses the Tasman District, Nelson City, Marlborough District, and Kaikoura District. Based on weather data from Nelson.

H1 Climate Zone 4:

• ‘RR’ - Covers the Rotorua District. Based on weather data from Rotorua.

• ‘TP’ - Includes the Taupō District, Ruapehu District, and the part of the Rangitikei District north of 39°50'S (-39.83). Based on weather data from Tūrangi.

• ‘WI’ - Encompasses the Tararua District, Upper Hutt City, Masterton District, Carterton District, and South Wairarapa District. Based on weather data from Masterton.

• ‘WC’ - Covers the Buller District, Grey District, and Westland District. Based on weather data from Hokitika.

H1 Climate Zone 5:

• ‘DN’ - Includes part of the Waitaki District on the true right of the Otekaieke River, Dunedin City, and the Clutha District. Based on weather data from Dunedin.

• ‘CC’ - Encompasses the Hurunui District, Waimakariri District, Christchurch City, Selwyn District, Ashburton District, Timaru District, and Waimate District. Based on weather data from Christchurch.

H1 Climate Zone 6:

• ‘QL’ - Covers the Queenstown-Lakes District. Based on weather data from Queenstown.

• ‘OC’ - Includes the Mackenzie District, the part of the Waitaki District on the true left of the Otekaieke River, and the Central Otago District. Based on weather data from Lauder.

• ‘IN’ - Encompasses the Southland District, Gore District, and Invercargill City. Based on weather data from Invercargill.